EUCYCLOCERATIN AMMONITES FROM THE CALLOVIAN CHARI FORMATION, KUTCH, INDIA

EUCYCLOCERATIN AMMONITES FROM THE

CALLOVIAN CHARI FORMATION, KUTCH, INDIA

by S. K. JANA* , S. BARDHAN* and K. HALDER�

*Department of Geological Sciences, Jadavpur University, Kolkata 700032, India; e-mail: [email protected]�Department of Geology, Durgapur Government College, Durgapur 713214, India

Typescript received 29 January 2002; accepted in revised form 24 June 2004

Abstract: The subfamily Eucycloceratinae Spath, 1928,

belonging to the family Sphaeroceratidae, is an important

Indo-Madagascan faunal element and is reported here from

the Callovian of Kutch, India. Previously the subfamily was

considered to consist of 14 morphospecies placed in four

morphogenera. The present study is based on re-examina-

tion of the type material and more than 350 new speci-

mens, collected with secure stratigraphical control, from

sections in mainland Kutch. It reveals that the subfamily

includes only two highly variable monospecific genera:

Eucycloceras Spath, 1924 and Idiocycloceras Spath, 1928.

Dimorphism in Eucycloceratinae, which was not previously

recognized, is firmly established. Cladograms have been

constructed, based on numerous morphological characters,

which show relationships among different subfamilies of

the Sphaeroceratidae and genera of the Macrocephalitinae

and Eucycloceratinae. The palaeobiogeography and evolu-

tion of the Eucycloceratinae are discussed in the light of

the new data.

Key words: Middle Jurassic, Ammonoidea, Eucycloceras,

Indo-Madagascan Province, phylogeny, cladistics.

Several exhaustive monographic treatments illustra-

ting a spectacular range of intraspecific morphological

variability are now available for Jurassic (e.g. Westermann

and Calloman 1988) and Cretaceous (e.g. Klinger and

Kennedy 1989) ammonite species. A direct result of these

studies is the drastic reduction of many previously estab-

lished morphospecies or morphogenera into a single bio-

species. This has helped remove pseudodiversity patterns,

and prompted reconsideration of many evolutionary

trees.

We consider the studies of Callomon (1985) to be an

excellent example of such work. Based on his ideas, we

have revisited the subfamily Eucycloceratinae, which con-

stitutes an important faunal element of the Callovian of

the Indo-Madagscan Faunal Province. We have shown

that failure to recognize the great intraspecific variability

and sexual dimorphism within the eucycloceratin popula-

tion led early workers to create a plethora of species.

These essentially are morphospecies or morphogenera,

and have little evolutionary significance. The present

investigation has not only unearthed numerous additional

specimens, but also was undertaken within a secure strati-

graphical framework. It reveals that many of the previ-

ously described species are essentially contemporaneous,

being restricted to within a single faunal horizon, or

at best a subzone. They show continuous horizontal

variation. However, the population may be sharply divi-

ded due to sexual dimorphism, an aspect overlooked by

early workers who failed to recognize this feature and

considered sexual variants as distinct genera.

The subfamily Eucycloceratinae of the family Sphaero-

ceratidae has not been studied in detail since Spath’s

(1928–33) work. He incorporated the four genera Notho-

cephalites, Eucycloceras, Subkossmatia and Idiocycloceras

within it. They are endemic to the Indo-Madagascan

Faunal Province and, as the new stratigraphical data

reveal, span a brief period of geological time from the lat-

est Early Callovian to early Middle Callovian. In Kutch

the appearance of this subfamily is coeval with that of the

Reineckeinae, at a time when the ancestral Macrocephalit-

inae were on the verge of regional extinction.

Spath’s four eucycloceratin genera include 14 species.

Most of these species were based on single specimens and

the holotypes are mostly fragmentary or preserved with

incomplete body-chambers. They are re-examined here

along with over 350 additional specimens. Detailed mor-

phological and morphometrical analyses reveal that, in

many cases, type species fall within the range of variability

of a single biospecies. Two of the four existing genera

(Eucycloceras and Idiocycloceras) survive close scrutiny and

form monospecific assemblages. The former is found in

the lower (older) stratigraphical horizon, but has strati-

graphical overlap with the latter. Most of the smaller spe-

cies of Subkossmatia, which closely resemble the inner

[Palaeontology, Vol. 48, Part 4, 2005, pp. 883–924]

ª The Palaeontological Association 883

whorls of Eucycloceras, are considered to be microconch

variants of Eucycloceras. The larger Subkossmatia species

have been relegated to members of Idiocycloceras. Idiocyc-

loceras is also found to be sexually dimorphic, although

microconchs were unknown until now. Nothocephalites is

excluded from Eucycloceratinae and placed within Macro-

cephalitinae.

Westermann and Wang (1988) assigned the Himalayan

genus Grayiceras Spath to the Eucycloceratinae. They

reported it from a condensed sequence in Tibet ranging

from the Upper Bathonian to Middle Callovian, although

it was previously described from the Oxfordian Spiti

Shale. We argue against the inclusion of Grayiceras s.s.

within the subfamily Eucycloceratinae and suggest that

the Tibetan forms perhaps belong to different eucyclocer-

atin species.

SUBFAMILY EUCYCLOCERATINAE:A HISTORICAL PERSPECTIVE

Spath (1928) first introduced the subfamily and included

four genera. He described two species of the type genus

Eucycloceras: E. eucyclum (Waagen), the type species, and

E. pilgrimi Spath. Waagen’s only specimen (1875, pl. 35,

fig. 1; here refigured in Pl. 1, fig. 1a–c) of Stephanoceras

eucyclum, which is an adult macroconch with partially

preserved body-chamber, was designated holotype. E. pil-

grimi is represented only by a small but complete adult.

Spath (1928) described six species of Subkossmatia of

which four (S. opis, S. obscura, S. coggin-browni and

S. discoidea) are small. They intergrade both morphologi-

cally and morphometrically (see below) and form a con-

tinuous series with E. pilgrimi. These smaller forms

closely resemble inner and intermediate whorls of E. eucy-

clum, which is a macroconch. The holotype of the latter,

and our recent collection of numerous specimens, indi-

cate that the macroconchs show limited intraspecific vari-

ability, but are marked by strong allometry during

ontogeny. The smaller species of Subkossmatia, as well as

E. pilgrimi, resemble different ontogenetic stages of the

macroconch. They are considered as variants, which

together with the type species, represent the enormously

variable microconch of a single species. Thus in E. eucy-

clum, the macroconch and the different microconchiate

forms are essentially sexual dimorphs of a single biospe-

cies. Interestingly, they are found in the same stratigraph-

ical interval and at the same localities. They thus

represent a widely variable monospecific assemblage (cf.

Callomon 1985). One notable exception from the usual

pattern of dimorphism in Jurassic ammonites is that the

dimorphism itself varies; the different ontogenetic stages

of adult macroconch phragmocones are replicated by the

different microconch adults. Hence, the notion that

dimorphism is a powerful tool for species discrimination

(Callomon 1971) has to be treated with caution. We

know only one other example from the Placenticeras kaff-

rarium population in the Cretaceous where enormous in-

traspecific variability has also been affected by the varying

nature of the dimorphism (see Klinger and Kennedy

1989; Bardhan et al. 2002).

Idiocycloceras of Spath (1928) also suffers from exces-

sive subjective splitting which has resulted in the creation

of several species, namely I. perisphinctoides (the type spe-

cies), I. singulare, I. dubium and I. sp. indet. The type

specimens are monotypic holotypes and represent septate

macroconchs, except that of I. singulare which is an

almost complete adult. They resemble the larger Subkoss-

matia ramosa and S. sp. indet., and many specimens

recently collected by us. All come from the same localities

and coeval levels, and intergrade morphologically. They

appear to be nothing more than different morphospe-

cies ⁄morphogenera, and in fact comprise a continuous

series. They form a monospecific assemblage within a very

narrow stratigraphical interval, representing a wide range

of variability of a single biospecies. The microconchs of

Idiocycloceras were previously unknown, but they are

recognized here on the basis of many new specimens. The

nature of dimorphism closely corresponds with that of

Eucycloceras, but the microconchs of Idiocycloceras show

less variability. The macroconch of Idiocycloceras is the

most evolute of the Sphaeroceratidae.

Eucycloceras and Idiocycloceras share many synapomor-

phies, such as an evolute shell with long primaries on the

outer whorls, the disappearance of secondaries rendering

the venter smooth on the last whorl of the adult macro-

conch (unlike those of macrocephalitins where loss of rib-

bing starts from the inner flanks producing smooth whorl

sides), protracted suture and the nature of dimorphism,

and evolute microconchs with ribbing persistent to the

end. However, both genera have their respective apomor-

phies (see below). For example, Eucycloceras macroconchs

develop adorally concave primaries on the adult body-

chamber.

Nothocephalites Spath appears to be quite different

from the eucycloceratin bauplan. It has a smooth adult

body-chamber, involute shell and short primaries, and

thus shares many plesiomorphic characters with macro-

cephalitins, especially with the endemic and older Macro-

cephalites formosus Spath. However, it has apomorphies

like fine and dense ribs. In the macroconch, both prima-

ries and secondaries suddenly disappear at the beginning

of the adult body-chamber. N. asaphus, the type species,

is considered here as a microconch (maximum diameter

154 mm) and N. semilaevis as a macroconch (maximum

diameter 230 mm). The former is characterized by having

a protracted suture like that of eucycloceratins (Spath

1928; Westermann and Wang 1988). We interpret the

884 PALAEONTOLOGY, VOLUME 48

suture as an evolving feature (see details in ‘Remarks’

section) and, in this respect, Nothocephalites shows an

evolutionary link between Macrocephalitinae and

Eucycloceratinae. Our cladistic analysis also reveals that

Nothocephalites is closer to Macrocephalites and we, fol-

lowing Thierry (1978) and Krishna and Westermann

(1987), retain it within the Macrocephalitinae but as a

distinct genus. In conclusion, Eucycloceratinae comprises

two genera: Eucycloceras Spath, 1924 (type genus) and Idi-

ocycloceras Spath, 1928.

SYSTEMATIC POSITION OFGRAYICERAS

Grayiceras is a problematic Himalayan genus previously

reported from Spiti (Spath 1923, 1924, 1928) and more

recently from southern Tibet (Westermann and Wang

1988). Spath proposed the genus, but did not define it,

and considered it an essentially Oxfordian or younger

form. He described several species of which only two sur-

vived later scrutiny (for detailed history of the genus, see

Arkell 1955 and Westermann and Wang 1988). These two

species are G. nepaulenese (Gray) and G. koeneni (Uhlig);

they are characterized by long primary ribs and protrac-

ted septal suture, i.e. two symplesiomorphic features typ-

ical of the early Mid-Callovian eucycloceratins. The type

specimens of G. nepaulense (see Westermann and Wang

1988, pl. 22, figs 1–3, pl. 23, fig. 1) seem to be micro-

conchs resembling one of the variants (infrasubspecies

obscura) of Eucycloceras. G. nepaulense shows similar

coarse ornamentation to the end without any loss of

strength and egression of the adult umbilical seam, and

inclined umbilical wall. On the other hand, G. koeneni

(Text-fig. 1A–C), which is a large body-chamber fragment

resembling Spath’s ‘Subkossmatia ramosa ⁄ Idiocyclocerassingulare’ (see also Westermann and Wang 1988), is in

fact a macroconch with characteristic coarse, distant, lon-

ger primaries. This ribbing style characterizes typical eu-

cycloceratin macroconchs compared with the short

primaries of the macrocephalitins. The problem is where

to place Grayiceras of the Oxfordian Spiti Shale. Are they

eucycloceratins or heterochronous homeomorphs? In the

evolutionary history of the sphaeroceratids, homeomor-

phism is apparent and widespread. Early Callovian

macrocephalitins have notorious homeomorphs among

Oxfordian mayaitins. Every exterior aspect, including

ornamentation, shell shape and septal suture, and even

interior morphology, of the macrocephalitins has a coun-

terpart among the mayaitins (Callomon in Donovan et al.

1981). Even the short primaries and the radial suture line

are mimicked. It is commonly agreed that the temporal

hiatus (Late Callovian–?Early Oxfordian) between these

two groups marks the distinction at subfamily level. Simi-

larly, the stratigraphically well constrained (near the

Lower ⁄Middle Callovian Substage boundary) eucyclocera-

tins of the Indo-Madagascan Faunal Province are strati-

graphically and geographically separated from Grayiceras

of the Tethyan Himalaya. Recently, it has been shown

that mayaitins include forms that have both radial and

protracted suture lines, e.g. Mayaites with radial, and

Epimayaites, Paryphoceras, Dhosaites and Prograyiceras

with protracted sutures (Westermann and Wang 1988).

This suggests that the suture was rapidly evolving, but

possibly with the gene(s) regulating the radial sutural

patterns remaining suppressed during the Mid-Callovian

A B C

TEXT -F IG . 1 . Grayiceras koeneni (Uhlig) [M]; A, lateral, B, apertural, C, ventral views; GSI 10014, bodywhorl fragment, retention of

secondaries indicate an immature shell; from Spiti Shale, ‘Gieumal’, Spiti; · 0Æ5.

JANA ET AL . : CALLOVIAN AMMONITES FROM KUTCH, INDIA 885

TEXT-F IG . 2 . Map of Kutch showing

important eucycloceratin-bearing

localities; see text-figures 3–6 for details.

TEXT -F IG . 3 . Stratigraphical column of the Jumara section illustrating lithostratigraphy, biostratigraphy and vertical distribution of

eucycloceratins and other important ammonite taxa; see Text-figure 2 for location.


(cf. Callomon in Donovan et al. 1981). Hence, we believe

that Grayiceras should be included within the subfamily

Mayaitinae, but as a distinct genus retaining the plesio-

morphic long primaries. It should be noted that other

mayaitins are also reported from the same horizons in the

Spiti area. They were described by Uhlig (1910b, pls 77,

81) as ‘Macrocephalites cf. maya’ and ‘Simbirskites n. sp.

ind.’, which according to Spath (1927–33) and Wester-

mann and Wang (1988) correspond well with Epimaya-

ites, especially E. falcoides Spath.

Grayiceras from southern Tibet (Westermann and

Wang 1988) creates further confusion. The area is tecton-

ically disturbed and the succession is interrupted by long

hiatuses. The ancillary taxa within the Grayiceras

assemblage are zonal indices of different ages. For exam-

ple, Macrocephalites cf. etheridgei, claimed by Westermann

and Wang (1988) to be from the Lower Callovian of the

Sula Islands and New Guinea (Indo-Pacific Faunal Prov-

ince), is a Middle Bathonian species, as recognized

by Westermann and Callomon (1988). Macrocephalites

cf. macrocephalus is a European species that comes from

the basal Callovian. Subkossmatia cf. opis, if correctly

identified, denotes a precise time interval straddling the

Early ⁄Middle Callovian boundary in the Indo-Madaga-

scan Faunal Province, especially in Kutch.

Thus it appears that the ferrugenous oolitic horizon

containing Grayiceras in southern Tibet may represent a

condensed sequence, and is certainly not younger than

Mid-Callovian. The species described were based on limi-

ted sample sizes and incomplete preservation. Subkossmatia

TEXT -F IG . 4 . Stratigraphical column of the Jara section illustrating lithostratigraphy, biostratigraphy and vertical distribution of



cf. opis is based on a few fragmentary specimens only,

one of which was figured (Westermann and Wang 1988,

pl. 23, figs 8–9). From the description and figure it

appears that it may represent a microconch variant of

Eucycloceras. Similar observations can be made on two

body-chamber fragments of G.? nepaulense (their text-

fig. 12A–B). They appear to be close to our larger micro-

conch variant of Eucycloceras, E. opis var. obscura. The

lectotype and paralectotype of their new species G.? waa-

geni significantly come from the Oxfordian Spiti Shale,

i.e. Giumal Sandstone, and are morphologically different

from the Callovian Tibetan specimens (their pl. 24,

figs 1–6). The Spiti specimens are compressed, involute

and relatively densely and finely ribbed in the adult stage.

Moreover, they lack characteristic long primaries, thus

perhaps resembling Epimayaites. On the other hand, Callo-

vian Tibetan forms have fine ribbing with long primaries,

and thus come close to Eucycloceras microconchs. How-

ever, this Tibetan population is more inflated and involute

than the Kutch population. G.? gucuoi sp. nov. (Wester-

mann and Wang 1988, pl. 24, figs 7–14, text-fig. 12C–E)

likewise resembles a microconch of Idiocycloceras, being

evolute (U ⁄D ¼ 0Æ25–0Æ30), depressed (B ⁄H ¼ 1Æ20–1Æ50)and coarsely ornate with biplicate ribs. It is, however, smal-

ler (D �60–70 mm) and relatively less evolute than I. peri-

sphinctoides [m]. We believe that while Grayiceras s.s. of

the Oxfordian belongs to the Mayaitinae, their alleged

Callovian counterparts reported from Tibet should be con-

sidered as a distinct population within the Eucyclocerati-

nae.

TEXT -F IG . 5 . Stratigraphical column of the Keera section illustrating lithostratigraphy, biostratigraphy and vertical distribution of



STRATIGRAPHY

The Kutch Basin was initiated during the Middle Jurassic

fragmentation of Gondwana, and soon began to receive a

huge input of sediments due to repeated marine trans-

gressions (Biswas 1977). As sea connections opened up,

the basin received many immigrant faunas, mostly from

the European Tethys. In this new habitat the European

fauna rapidly speciated, producing a characteristic ende-

mic assemblage known as the Indo-Madagascan or Ethio-

pian Fauna. It includes corals (Gregory 1900; Pandey and

Fursich 1993), gastropods (Das et al. 1999; Jaitly et al.

2000), brachiopods (Mukherjee et al. 2002, 2003), nauti-

loids (Halder 2000) and ammonites (many authors

including Waagen 1875 and Spath 1924, 1927–33). While

much of the fauna has been treated monographi-

cally, stratigraphical data have remained subordinate to

taxonomy.

Lithostratigraphy

The major lithostratigraphical units, in ascending order,

are the Patcham, Chari, Katrol and Bhuj formations.

Mesozoic rocks cover nearly half of the area of Kutch,

including both the mainland and three ‘islands’ separated

by an intervening expanse of salt-flat known locally as the

Rann. The regional structure consists of three parallel,

TEXT -F IG . 6 . Stratigraphical column of the Jhura section illustrating lithostratigraphy, biostratigraphy and vertical distribution of



north-west–south-east-orientated, anticlines. The Jurassic

rocks are best developed in the central anticline (Wynne

1872), situated towards the north of the mainland. These

anticlines are superimposed by a set of zones of culmin-

ation that crop out as topographical domes, as at Jara, Ju-

mara, Keera and Jhura (Text-fig. 2). The domal outcrops

are disturbed by igneous intrusion and their northern

flanks are truncated by an east–west-trending fault. The

older formations (Patcham and Chari) are present as in-

liers and are surrounded by the younger Katrol Forma-

tion.

Ammonites are abundant in the two older formations,

despite the frequent spatiotemporal facies changes (Furs-

ich et al. 1994; Mukherjee et al. 2002; J. H. Callomon,

pers. comm. 2000). The Chari Formation is represented

by a heterolithic facies association consisting of shale,

limestone and sandstone, deposited in a mid-shelf

environment. While the Lower Callovian includes a domi-

nantly shale-limestone (packstone ⁄wackestone) associ-

ation, the Middle Callovian starts with siliciclastics.

Significant sedimentological work and detailed facies

analyses are now available (Datta 1992; Fursich et al.

1992; Fursich and Oschmann 1993). The arenaceous fa-

cies of the Middle Callovian represent a shoaling-upward

phase (Datta 1992; Fursich and Oschmann 1993). This fa-

cies is monotonous in the field, consisting of yellowish

grey sandstone, that is commonly multistoreyed, massive,

with a coarsening-upward sequence, devoid of bioturba-

tion and with large-scale cross-beds. Close study reveals

the presence of three units. They are persistent, forming

west–east ridges on mainland Kutch, with increasing

thickness and decreasing fossil-bearing horizons that

reflect the direction of the palaeoshoreline.

Most of the ammonite specimens are exquisitely pre-

served with their original shell intact and easily recover-

able from the sediments. Field investigations yielded more

than 350 eucycloceratin specimens, which were collected

from four important sections across the mainland

(Jumara, Jara, Keera and Jhura). Detailed lithostratigraph-

ical successions of each section, along with the vertical

distribution of the major ammonite species, is shown in

Text-figures 3–6.

Jumara is the stratotype of the Chari Formation (Text-

fig. 3). It is situated about 100 km north-west of Bhuj,

the district town of Kutch, and is named after the nearby

village. It is an eroded anticlinal dome with an inlier

occupied by the older Patcham Formation. Rajnath

(1932) first studied the Middle Jurassic rocks of Jumara

and mapped the area at a scale of 4 inches to 1 mile. The

Chari Formation, which borders the Patcham Inlier,

occurs as an elliptical outcrop. The beds show radial dip

which are mostly gentle, but may be up to 60 degrees

towards the northern flank. At Jumara the uppermost

Bathonian bed (Bed 4) of the Chari Formation is a lime-

stone (wackestone) 15 m thick. The lowermost bed of the

Lower Callovian (Bed 5) is 10 m thick and comprises

repeated alternations of shale, white limestone (wacke-

stone) and reddish or brownish limestone (pack-

stone ⁄ grainstone). Chevron cross-stratification is

occasionally present in the wackestone but the packstone

and grainstone are relatively massive. Bed 6 is represented

by a shale 16 m thick interbedded with thin, parallel-

sided, dark brown ferruginous limestone. The uppermost

bed of the Lower Callovian (Bed 7) is a thick shale with

coquina bands. This bed is 17 m thick and the first

appearance of the eucycloceratins is recorded from the

top part. The lowermost bed of the Middle Callovian

(Bed 8) is a yellowish grey multistoreyed sandstone 4 m

thick. This unit is overlain by a siltstone 6 m thick (Bed

9) and records the uppermost occurrence of the eucyclo-

ceratins. The immediately younger unit (Bed 10) is a yel-

lowish grey sandstone 15 m thick. The overlying unit

(Bed 11) consists of repeated alternations of greenish grey

shale ⁄ ironstone and white limestone (wackestone). This

bed is 70 m thick and is the uppermost unit of the Mid-

dle Callovian. The lowermost bed of the Upper Callovian

is a ferruginous sandstone 5 m thick (Bed 12) with bored

pebbles of white limestone (wackestone).

Jara is another anticlinal outcrop. It is c. 10 km north-

west of Jumara and named after a village in the vicinity.

Owing to severe weathering the profile of the dome is low

and the contacts between the beds are not always sharp.

However, because of the weathering, it is possible to

recover fossils easily, and the specimens collected are

mostly in an excellent state of preservation. The Callovian

rock sequence of Jara (Text-fig. 4) is similar to that of

Jumara, except that the base of the Lower Callovian is not

exposed. At Jara eucycloceratins are found in Beds 2 and 3.

Keera is an elliptical anticlinal dome situated c. 50 km

north-west of Bhuj. It is named after a hillock composed

of basic rocks in the northern part of the dome. The

older rocks are resistant and occupy high areas at the cen-

tre. They are surrounded by younger beds (for a detailed

lithological map, see Mitra et al. 1979). The lowermost

unit of the Chari Formation (Bed 1) at Keera (Text-

fig. 5) is a grey limestone (bioclastic grainstone) 15 m

thick. This is overlain by a sequence 65 m thick (Bed 2)

of golden coloured oolitic limestone (grainstone and

packstone). It is multistoreyed and cross-stratified (both

chevron and hummocky). There are at least three levels

where bored pebbles (wackestone) are sporadically strewn.

Ooids vary in shape and size, and show various internal

structures. The ooids are heavily impregnated with goeth-

ite, which is responsible for their characteristic golden

lusture. Kheraiceras hannoveranum, a typical Late Batho-

nian ammonite, has been found in the lower part of Bed

2 (Jana et al. 2002), indicating that the Upper Batho-

nian ⁄Lower Callovian boundary passes through this bed.


The allotype of Eycycloceras opis comes from the upper

part of this bed. The immediately younger bed (Bed 3) is

a grey shale ⁄marl 20 m thick with alternating reddish

brown to grey packstone. The uppermost bed of the

Lower Callovian (Bed 4) is a grey oolitic bioclastic grain-

stone (coquina) 5 m thick. The Middle Callovian litho-

stratigraphical sequences are similar to those of the

Jumara and Jara, and the uppermost level from which

eucycloceratins are recorded at Keera is Bed 6.

Jhura is another elliptical dome, situated c. 25 km

north-west of Bhuj, and named after the nearby village.

The same major lithologies of the western mainland can

be traced here but the individual beds are thicker, with

increasing siliciclastic content. This suggests that Jhura lies

nearer to the palaeoshoreline. Here, resistant and thick

rocks of the Patcham and Chari formations occupy a lar-

ger area and form ranges with hills up to 300 m high with

deep canyons between. The dome, like others, opens

towards the north and is drained by the Kaila River and

many subsidiary streams. Much of the older Patcham For-

mation is exposed at the core. The older beds are only

accessible through some passes that constitute dry streams

flowing towards the north. At Jhura the Callovian rock

sequence (Text-fig. 6) is much thicker than that of the

other areas studied. Here the uppermost Bathonian bed

(Bed 4) is a hard, slabby, white limestone 15 m thick, and

is lithologically similar to Bed 4 of Jumara. The lowermost

unit of the Lower Callovian (Bed 5) is a sequence of shale-

limestone alternations 65 m thick with a hard compact car-

bonate facies that is 1 m thick at the base. The uppermost

unit of the Lower Callovian (Bed 6) is a unit of shale-lime-

stone alternations 96 m thick with coquina bands. The

lowermost unit of the Middle Callovian is a red massive

sandstone bed 31 m thick (Bed 7). This is followed by an

oolitic limestone 69 m thick (Bed 8); eucycloceratins occur

in this unit. The overlying unit (Bed 9) is a 46-m-thick

sandstone that is equivalent to Bed 10 of Jumara, Bed 4 of

Jara and Bed 7 of Keera. The younger units are similar to

those of the other areas studied.

Biostratigraphy

Many stratigraphical schemes encompassing the Callovian

have been proposed and continue to be debated (e.g.

Biswas 1977; Krishna 1984). We, along with others, have

been revising pre-existing schemes as new data emerge

(Bardhan et al. 1994). Recently we have subdivided the

Lower Callovian Substage on the basis of diverse Macro-

cephalites (Bhaumik et al. 1993; Datta et al. 1996) and

Kheraiceras species (Jana et al. 2000; Bardhan et al. 2001),

retaining many of the existing subzones but proposing

several new faunal horizons. A newly proposed general-

ized biozonation based on ammonites for the Middle

Callovian of Kutch, along with a tentative correlation

with the Sub-Mediterranean biostratigraphical schemes, is

presented in Text-figure 7. Systematic collecting of

ammonites has enabled us to refine the position of exist-

ing faunal horizons in addition to introducing many new

ones. These horizons are easily recognizable in the field,

especially in the western part of the mainland (Jara, Ju-

mara, Keera).

The proposed zones of the Middle Callovian strata are

the anceps and reissi assemblage zones. The former

includes three subzones, anceps, opis and indicus in

ascending order. The reissi Assemblage Zone has been fur-

ther subdivided into two subzones, reissi and aberrans in

ascending order. The detailed ammonite faunal assem-

blages are given below:

anceps horizon. This is marked by the disappearance of

Kheraiceras, Macrocephalites spp., Inodocephalites spp.,

Nothocephalites semilaevis and Kamptokephalites dimerus;

K. lamellosus is very rare; Idiocycloceras makes its first

appearance; Eucycloceras opis, Reineckeia anceps, R. tyr-

anniformis, Collotia oxyptycha, Choffatia recuperoi,

C. cobra and C. pedargatus of the preceding semilaevis

horizon continue.

tyranniformis horizon. This is marked by the disappear-

ance of Macrocephalitinae; Reineckeia tyranniformis is fre-

quent; all other species of the preceding horizon continue.

opis horizon. Eucycloceras opis is dominant; all other

species continue.

perisphinctoides horizon. Idiocycloceras perisphinctoides

is the dominant faunal element; first appearance of the

genus Phlyticeras; all other species continue.

cobra horizon. This is marked by the disappearance of

Eucycloceratinae and the inception of the genus Indo-

sphinctes; reineckeiins, choffatins and Phlycticeras continue.

indicus horizon. Indosphinsctes indicus very abundant;

Phlycticeras is common; all other species continue.

gigantea horizon. Reineckeia anceps, R. tyranniformis

and Indosphinctes disappear; Collotia gigantea, R. reissi,

Erymnoceras jumarensis first appear; Obtusicostites obtusi-

costa and Hubertoceras arcicosta common; choffatins con-

tinue.

reissi horizon. Reineckeia reissi is the most abundant

taxon; Collotia gigantea and choffatins continue.

aberrans horizon: Subgrossouvria aberrans is the most

abundant taxon; R. reissi, C. gigantea and choffatins con-

tinue; first appearance of R. rota; Hecticoceras (Kheraites)

ferrugineum and H. (Putealiceras) trilineatum common.

Chronostratigraphy and correlation with other regions

Demarcation of stage boundaries and correlation of regio-

nal standard zonations with those of stratotypes are two of

the central concerns of Kutch workers (Callomon 1993;


Jain et al. 1996). The Bathonian ⁄Callovian boundary has

now been firmly established and is well correlated with the

European Tethys and Pacific (Kayal and Bardhan 1998;

Bardhan et al. 2001). The majority of workers consider that

the Lower Callovian ⁄Middle Callovian Substage boundary

coincides with the top of the semilaevis Subzone (Jana

et al. 2000; Bardhan et al. 2001; Mukherjee et al. 2003).

Spath (1928–33) subdivided the Middle Callovian of

Kutch into two zones: rehmanni and anceps. The rehmanni

Zone encompasses the present eucycloceratin-bearing

beds. However, European Rehmannia rehmanni is very

poorly known (Datta 1992) or altogether absent (Cariou

and Krishna 1988) in India. Indeed, the reineckeiin species

that is abundant in this zone is R. indosabauda, which is

now synonymized with R. anceps (Cariou and Krishna

1988). R. anceps is a zonal index of Sub-Mediterranean

France and a chronostratigraphical zone marking the base

of the Middle Callovian has been named after it (Cariou

1984). The base of the Middle Callovian is thus directly

correlated with the base of the anceps Zone of France and

is followed here (see also Krishna and Thierry 1987;

Cariou and Krishna 1988; Jana and Das 2002; Mukherjee

et al. 2003). Spath (1927) named the superjacent anceps

Zone on the basis of Waagen’s (1875) Perisphinctes anceps,

which he himself redesignated later (Spath 1928) as Reine-

ckeia reissi. R. reissi is abundant and ubiquitous at this

level and deserves to be the replacement zonal index.

Krishna and Thierry (1987), however, introduced a coron-

atum Zone to replace the ‘anceps Beds’ of Spath (1927–33)

and matched this level with the Sub-Mediterranean coron-

atum Zone. This zone in Kutch was based on a single spe-

cimen of an endemic species, Erymnoceras jumarensis, and

is thus tentative. Our systematic field collection has

revealed that R. reissi extends to the top of the Middle

Callovian. The lowermost faunal horizon of the coronatum

Zone of France, i.e. villanyensis horizon, yields Collotia gig-

natea (Cariou 1984). This species is common from the

base of reissi Zone (A. Kayal, pers. comm. 2000) and

Cariou and Krishna (1988) also reported a single specimen

at Jumara from the base of their coronatum Zone. Thus

the base of the reissi Zone can be confidently matched with

the base of the coronatum Zone of France. The reissi Zone

TEXT -F IG . 7 . Zonation of the Middle Callovian Substage of Kutch, India, and its correlation with zones of the Sub-Mediterranean

Province.


of Kutch is subdivided into two subzones, i.e. the lower

reissi Subzone and the upper aberrans Subzone. The aber-

rans Subzone is dominated by Subgrossouvria aberrans.

However, the subzone boundaries of the reissi Zone are

difficult to correlate with those of the contemporaneous

coronatum Zone of France because of the absence of any

cosmopolitan ammonite species.

The anceps Zone of France is subdivided into two sub-

zones: stuebeli and tyranniformis. We have been able to

subdivide the anceps Zone of Kutch into three subzones:

anceps, opis and indicus. Recent study (Kayal, pers. comm.

2000) reveals that R. anceps and R. stuebeli are morpho-

logically very close and have the same biogeographical

and biostratigraphical distributions, and appear to be

conspecific (monospecific assemblage of Callomon 1985).

Thus the anceps Subzone of Kutch matches well the stue-

beli Subzone of France. However, R. tyranniformis occurs

at a higher chronostratigraphical level in France (ranging

from the blyensis horizon, tyranniformis Subzone to baylei

horizon, baylei Subzone of the coronatum Zone) than in

Kutch where it first appears in the semilaevis horizon of

the Lower Callovian and continues to the top of the

anceps Zone. Spath (1928) reported the holotype of

R. tyranniformis from the Golden Oolite of Keera, which

also yields Nothocephalites semilaevis.

Eucycloceratins, however, have different distribution

patterns. The older genus Eucycloceras first appears in the

semilaevis horizon. The holotype of Spath’s (1928) Eucyc-

loceras eucyclum comes from the Golden Oolite of Keera.

He later mentioned the co-occurrence of Eucycloceras

with Nothocephalites semilaevis in the same matrix (Spath

1933, p. 676) and emphasized that none of the eucyclo-

ceratin species passes beyond the ‘anceps Beds’. His table 4

(pp. 716–717) shows the upper limit of the subfamily is

his Lower anceps Beds. Our repeated field investigations

support Spath’s (1933) later view and reconfirm its lower

limit extending back to the semilaevis horizon. To date

we have collected only two specimens of Eucycloceras opis,

one of each sexual variant, from this level. Idiocycloceras

appears only from the basal anceps horizon of the Middle

Callovian and both genera co-occur up to the peri-

sphisctoides horizon before they disappear dramatically.

The two faunal horizons named after them are not always

distinguishable in the field, particularly eastwards on the

mainland.

The substage boundary between the Middle and Upper

Callovian is secured by the discovery of several specimens

of Reineckeia rota (A. Kayal, pers. comm. 2000).

CLADISTIC ANALYSES

Eucycloceratinae is a small clade with two genera that are

restricted to the Lower Callovian ⁄Middle Callovian Sub-

stage boundary. They belong to the family Sphaerocerati-

dae, which is clearly recognizable as a monophyletic

group on the basis of at least three major symplesiomor-

phic characters: non-lappeted microconch, low dimorphic

size ratio and uninterrupted ribbing across the venter.

The phylogenetic relationships among the members of

this family remain poorly understood. For example,

Donovan et al. (1981) questionably retained Eucyclocerat-

inae as a subfamily. The present cladistic analyses were

performed using 25 shell morphology characters to study

phylogenetic relationships among the five existing

subfamilies. The cladograms are based on PAUP, 4.0b 10

version (Swofford 1998). All characters are weighted

equally and unordered. The characters are given in Table 1

and the data matrix used is given in the Appendix.

Otoitidae has been considered as an ancestral outgroup

TABLE 1 . List of characters used in the cladistic analyses of

Sphaeroceratidae subfamilies (see Text-fig. 8A–B).

1. Shell sharply ribbed: present (0); absent (1).

2. Complex septal suture: present (0); absent (1).

3. Dominant first lateral lobe: present (0); absent (1).

4. Well-developed umbilical lobe: present (0); absent (1).

5. Microconch ribbed to the end: present (0); absent (1).

6. Egression of adult body-chamber in microconch: present

(0); absent (1).

7. Non-lappeted microconch: present (0); absent (1).

8. Dimorphic size ratio: high (0); low (1).

9. Ventral discontinuity of ribbing: may be present (0); absent

(1).

10. Adult size of macroconch: small (0); large (1).

11. Variocostation (differentiated ribbing) of microconch: pre-

sent (0); absent (1).

12. Microconch with collar: present (0); absent (1).

13. Lateral tubercle ⁄ bullae in microconch: present (0); absent (1).

14. Terminal constriction in macroconch: absent (0); present (1).

15. Strength of ribbing in microconch: coarse (0); fine to coarse (1).

16. Adult whorl outline: planulate (0); sphaerocone (1); sph-

aerocone to oxycone (2); ovate to subtrapezoidal (3); sph-

aerocone to subelliptical (4).

17. Egression of adult body-chamber in macroconch: absent (0);

present (1).

18. Degree of involution of macroconchiate phragmocone: peri-

sphinctoid evolute (0); obvolute (occluded umbilicus) to

involute (1); involute (2); evolute (3).

19. Depressed inner whorl: present (0); absent (1).

20. Contracted aperture in macroconch: absent (0); present (1).

21. Contracted aperture in microconch: absent (0); present (1).

22. Occluded to strongly involute umbilicus in young micro-

conch: present (0); absent (1).

23. Strength of ribbing in microconch in comparison to that of

macroconch: strong (0); moderate (1); weak (2).

24. Length of primaries in outer whorl: short (0); long (1); both

(2).

25. Order of withdrawal of ribbing in macroconch: primaries

first (0); secondaries first (1).


(see Donovan et al. 1981) of Sphaeroceratidae. We have

deliberately chosen species that exhibit a reasonable

amount of variation among members of a genus or

higher taxon (such as subfamily and family). The majority

of these species represent type species of a genus and are

marked by asterisks in Table 2. Macrocephalitinae and

Mayaitinae are known to be homeomorphic (Donovan

et al. 1981; Thierry in Dommergues et al. 1989) and

therefore the homoplastic character states, such as radial

to protracted suture line, fine to coarse ribbing in the

macroconch and complete smoothness of body-chamber

of the macroconch, are excluded here. The PAUP search

has been performed using the branch and bound option,

which guarantees finding the shortest trees. Six trees have

been found, of which the strict consensus tree is shown

in Text-figure 8A. From these trees one is selected

(Text-fig. 8B) following Monks (2000, 2002), which

appears to be in agreement with the stratigraphical and

TABLE 2 . Species of outgroup Otoitidae and different subfamilies of Sphaeroceratidae used in the cladistic analyses described

here; *denotes type species. Stratigraphical ranges and palaeogeographical distribution are recorded, with all sources reported in

the text.

Taxa Stratigraphical range Palaeobiogeography

Otoitidae Mascke, 1907 Aalenian–Bajocian Cosmopolitan

Abbasites Buckman, 1921

*A. abbas (Buckman, 1921)

Aalenian Europe

Docidoceras Buckman, 1919

*D. cylindroides Buckman, 1919

Bajocian Europe, North Africa

Emileia Buckman, 1898

*E. brocchii (J. de C.Sowerby, 1818)

Middle Bajocian Cosmopolitan

Zemistephanus McLearn, 1927.

*Z. richardsoni (Whiteaves, 1876)

Middle Bajocian Pacific

Trilobiticeras Buckman, 1919

*T. trilobitoides Buckman, 1919

Middle Bajocian Europe, Western Australia

Otoites Mascke, 1907

*O. sauzei (Orbigny, 1846)

Middle Bajocian Cosmopolitan

Sphaeroceratinae Buckman, 1920. Bajocian Cosmopolitan except Boreal

Sphaeroceras Bayle, 1878

*S. brongniarti (J. de C. Sowerby, 1817)

Bajocian Europe, N. Africa, Persia, S. Alaska

Chondroceras Mascke, 1907

*C. gervillii (Sowerby, 1817)

Bajocian Europe, N. Africa, Caucasus,

New Guinea, America

Preatulites Westermann, 1956

*P. kruizingai Westermann 1956

Bajocian Pacific

Labyrinthoceras Buckman, 1919

*L. perexpansum Buckman, 1919

Middle Bajocian Europe

Frogdenites Buckman, 1921

*F. spiniger Buckman, 1921

Middle Bajocian Europe, Tibet, Canada

Eurycephalitinae Thierry, 1976 Upper Bajocian–

Middle Callovian?

Pacific

Eurycephalites Spath, 1928

*E. vergarensis (Burckhardt, 1903)

E. rotundus (Tornquist)

Lower Callovian East Pacific

Megasphaeroceras Imlay, 1973

M. magnum Riccardi and Westermann

Upper Bajocian East Pacific

Lilloetia Crickmay, 1930

*L. lillotensis Crickmay, 1930

L. steinmanni (Spath, 1928)

Upper Bathonian–

Middle Callovian?

Pacific

Xenocephalites Spath, 1928

*X. neuquenensis (Stehn, 1924)

X. gottschei (Tornquist, 1898)

Upper Bathonian–

Lower Callovian

Pacific

Macrocephalitinae Salfeld, 1921 Middle Bathonian–lower

Middle Callovian

South-west Pacific, Tethyan and

Indo-Madagascan Province

Macrocephalites (Macrocephalites) Zittel, 1884

*M. (M.) macrocephalus (Schlotheim, 1813)

M. (M.) bifurcatus bifurcatus Boehm, 1912

As above Europe, Madagascar, India (Kutch

and Himalayas), Indonesia, New Guinea


TABLE 2 . Continued.

Taxa Stratigraphical range Palaeobiogeography

M. (M.) bifurcatus intermedius (Spath, 1928)

M. (M.) mantataranaus Boehm, 1912

M. (M.) apertus (Spath, 1928)

M. (M.) keeuwensis Boehm, 1912

M. (M.) triangularis Spath, 1928

M. (M.) madagascariensis Lemoine, 1911

M. (M.) formosus (J. de C. Sowerby, 1840)

M. (M.) jacquoti (Douville, H., 1878)

M. (M.) verus Buckman, 1922

Macrocephalites (Indocephalites) Spath, 1928

*M. (I.) kheraensis Spath, 1928

M. (I.) chrysoolithicus (Waagen, 1875)

M. (I.) diademetus (Waagen, 1875)

Lower Callovian India, Madagascar, France

Macrocephalites (Pleurocephalites) Buckman, 1922

M. (P.) habyensis Spath, 1928

M. (P.) elephantinus (J. de C. Sowerby, 1840)

Lower Callovian Indonesia, India, Madagascar, England

Macrocephalites (Kamptokephalites) Buckman, 1922

M. (K.) lamellosus (J. de C. Sowerby, 1840)

M. (K.) dimerus (Waagen, 1875)

M. (K.) etheridgei Spath, 1928

Middle Bathonian–

lower Middle Callovian

Indonesia, India, Madagascar, France,

England

Macrocephalites (Dollikephalites) Buckman, 1923

M. (D.) subcompressus (Waagen, 1875)

M. (D.) gracilis Spath, 1928

Lower Callovian India, Madagascar, France, England

Nothocephalites Spath, 1928

N. semilaevis (Waagen, 1875)

*N. asaphus Sapth, 1928

upper Lower Callovian India, Madagascar

Eucycloceratinae Spath, 1928 Top of Lower Callovian–

lower Middle Callovian

Indio-Madagascan Province,

Himalayan Tethys

Eucycloceras Spath, 1924

*E. opis (J. de C.Sowerby, 1840)

As above India, Madagascar, Tibet

Idiocycloceras Sapth, 1928

*I. perisphinctoides Spath, 1928

Basal Middle Callovian India, Madagascar, Tibet

Mayaitinae Spath, 1928 Lower Oxfordian–Lower

Kimmeridgian

Indo-Madagascan Province,

Himalayan Tethys, Pacific (South)

Mayaites Spath, 1924

*M. maya (J. de C.Sowerby, 1840)

M. obesus Spath, 1928

M. smeei Spath, 1928

Oxfordian–Lower

Kimmeridgian

India, Madagascar, Indonesia

Mayaites (Araucanites) Westermann and Riccardi, 1975

*M. (A.) stipanicici Westermann and Riccardi, 1975

M. (A) reyesi Westermann and Riccardi, 1975

Oxfordian Argentina, Chile

Epimayaites Spath, 1928

E. polyphemus (Waagen 1875)

*E. transiens (Waagen 1875)

Oxfordian

E. falcoides Spath, 1928 India, Madagascar

Dhosaites Spath, 1924

*D. eliphantoides Spath, 1928

Oxfordian India, Madagascar

Paryphoceras Spath, 1928

*P. badiense Spath, 1928


Prograyiceras Spath, 1928

*P. grayi (Spath, 1924)


Grayiceras Spath (1923)

*G. nepaulenese (Gray, 1830–32)

G. koeneni (Uhlig, 1910)

Oxfordian India (only Himalayas)


palaeobiogeographical data (see Table 2). This tree has a

length of 29, consistency index of 0Æ8621 and a retention

index of 0Æ7143. Statistical tests like bootstrap and branch

decay (Bremer 1988) have also been performed using

PAUP and PAST (Hammer et al. 2003). The bootstrap

values for a group is the percentage of replicates support-

ing that group and it tests the robustness of tree topology

(Felsenstein 1985). Bremer support for a clade is the

number of extra steps a tree needs to be lengthened for a

given node to collapse; the greater the number of steps

the more robust the node (Monks 2000). The result of

both of these tests are given in Text-figure 8B.

The systematic position of Nothocephalites has been

debated for a long time. Here we advocate its inclusion

within the Macrocephalitinae. To test our proposed clas-

sification we have performed another cladistic analysis

and constructed a cladogram using 27 morphological

characters (Table 3) to document the geneological pat-

terns among the four genera Macrocephalites, Notho-

cephalites, Eucycloceras and Idiocycloceras. Lower

Callovian Tethyan Macrocephalites has been considered

as an outgroup. A single tree (Text-fig. 8C) has been

derived by the branch and bound option. This tree has

a length of 30, consistency index of 0Æ9333 and a retent-

ion index of 0Æ7143. The data matrix used is given in

the Appendix. Similarly, this cladogram fits perfectly

with stratigraphical and palaeobiogeographical data (see

Table 2). Data sources used here are taken from a range

of literature (Spath 1924, 1927–33; Basse and Perrodon

1951; Westermann 1956; Arkell et al. 1957; Stipanicic

et al. 1975; Thierry 1978; Donovan et al. 1981; Krishna

and Westermann 1987; Westermann and Callomon

1988; Westermann and Hudson 1991; Bhaumik et al.

1993; Datta et al. 1996; Parent 1997; Jana 2002) and

from personal observation.

SYSTEMATIC PALAEONTOLOGY

Abbreviations. Specimen numbers bear the following repository

institutional prefixes: GSI, Geological Survey of India, Kolkata;

JUM, Jadavpur University Museum, Kolkata. [M] and [m] des-

ignate macro- and microconch, respectively. Asterisks (*) against

items in synonymies indicate type specimens. The following let-

ters are used to indicate shell parameters: B, breadth of whorl;

D, diameter of shell; H, height of whorl from umbilical margin;

P, number of primaries per half whorl; S, number of secondaries

per half whorl; U, diameter of umbilicus.

Family SPHAEROCERATIDAE Buckman, 1920

Subfamily EUCYCLOCERATINAE Spath, 1928

Diagnosis. Evolute shell, inner whorls depressed and less

evolute; adult whorls mostly compressed. Strongly dimor-

phic in size and nature of ornamentation. Microconchs

have generally isocostate ribbing which continues to the

EXPLANATION OF PLATE 1

Figs 1–7. Eucycloceras opis (J. de C.Sowerby) [M]. 1a–c, allotype, adult with incompletely preserved body-chamber, GSI 2020, Golden

Oolite (Bed 2), Keera, photographically presented for the first time. 2, whorl section of an adult body-chamber, JUM 506, Bed 8,

Jhura. 3, almost complete adult, JUM 425, Bed 9, Jumara. 4, venter of almost complete adult, JUM 431, Bed 9, Jumara. 5a–b,

wholly septate, JUM 511, Bed 8, Jhura. 6, wholly septate, JUM 565, Bed 8, Jhura. 7, Adult phragmocone with inner whorls

exposed, JUM 428, Bed 6, Keera. Cross-marks indicate the position of adult end-phragmocone. All · 0Æ5.

A

B

C

TEXT -F IG . 8 . Cladograms showing phylogenetic relationships

of different subfamilies of Sphaeroceratidae with Otoitidae as an

outgroup (A–B). Strict consensus of the six most parsimonious

trees is shown in A, and the tree selected as best match with

stratigraphical and palaeobiogeographical data is shown in B.

Percentage bootstrap support (above 50%) and branch decay

values are also plotted (in squares and circles, respectively) on

the latter figure. The genus-level cladistic analysis of

Macrocephalitinae and Eucycloceratinae yields only a single tree,

which is also stratigraphically compatible; it is shown in C.


aperture and macroconchs have variocostate ribbing.

Body-chamber occupies three-quarters of the last whorl.

Macroconchs are the most evolute sphaeroceratids. Septal

suture protracted. Prosocline primary ribs become

increasingly longer, coarser and blunter during ontogeny.

Secondaries project strongly forward over venter near

1a 1b 1c

2

3 X

4

5a

67 5b

PLATE 1

JANA et al., Eucycloceras


aperture of microconchs, but continue up to varying dis-

tance with attenuated strength on venter of adult macro-

conch and finally disappear.

Range. Upper Lower Callovian–lower Middle Callovian, distri-

buted mainly in the Indo-Madagascan Faunal Province, with

rare excursions to the Himalayan Tethys.

Genus EUCYCLOCERAS Spath, 1924

Type species. Stephanoceras eucyclum Waagen, 1875; subsequent

designation by Spath, 1924–28; now recognized to be a synonym

of Ammonites opis J. de C. Sowerby (1840).

Eucycloceras opis (J. de C. Sowerby)

Plates 1–4; Plate 5, figures 1–4; Text-figures 9–12

*1840 Ammonites opis J. de C. Sowerby, pl. 23, fig. 9 [m].

1875 Stephanoceras opis (J. de C. Sowerby); Waagen,

p. 141, pl. 36, fig. 1 [m].

*1875 Stephanoceras eucyclum Waagen, p. 142, pl. 35

fig. 1 [M].

non1893 Ammonites (Stephanoceras) opis, Oldham, p. 228

[m].

1902 Ammonites opis J. de C Sowerby; Blake, p. 35 [m].

1910 Kossmatia? eucycla (Waagen); Lemoine, p. 29 [M].

1910 Macrocephalites opis (J. de C. Sowerby); Lemoine,

p. 30 [m]

1910 Macrocephalites opis (Waagen); Uhlig, a, p. 265

[m].

1910 Kossmatia eucycla (Waagen); Uhlig, a, p. 268 [M].

1913 Stephanoceras opis (J. de C. Sowerby); Smith, b and

c, p. 420 [m].

1924 Eucycloceras eucyclum (Waagen); Spath, p. 8 [M].

1924 Subkossmatia opis (J. de C. Sowerby); Spath, p. 11

[m].

1924 Macrocephalites? (Eucycloceras?) subcompressus

(Waagen); Spath, p. 21 (no. 248) [m].

1925 Eucycloceras eucyclum (Waagen); Spath, p. 209,

pl. 23, fig. 4a–b; pl. 25, fig. 4 [M]; pl. 27, fig. 7a–b

[m].

1928 Eucycloceras pilgrimi Spath, p. 209, pl. 27, fig. 6;

pl. 29, fig. 2 [m].


Figs 1–10. Eucycloceras opis (J. de C. Sowerby). 1–3, M. 1a–b, wholly septate, JUM 248, Bed 9, Jumara. 2, complete adult, JUM 505, Bed

8, Jhura; note dense growth striae near aperture. 3a–b, wholly septate, JUM 509, Bed 8, Jhura. 4–10, m, var A. 4, almost complete

adult with inner whorls exposed, JUM 261, Bed 6, Keera. 5a–b, complete adult, JUM 392, Bed 9, Jumara. 6a–c, paralectotype,

complete adult, JUM 371, Bed 5, Keera. 7a–c, complete adult, JUM 556, Bed 9, Jumara; note sharp umbilical edge and steep wall in

adult body-chamber. 8a–b, almost complete adult, JUM 372, Bed 6, Keera. 9, complete adult, JUM 433, Bed 9, Jumara; note

approximation of ribbing near aperture. 10, complete adult with appoximated ribs at the end, JUM 432, Bed 9, Jumara. All · 0Æ5.

TABLE 3 . List of characters used in the cladistic analyses of

Macrocephalitinae and Eucycloceratinae genera (see Text-fig. 8C).

1. Uncoiling of adult body-chamber: present (0); absent (1).

2. Nucleus whorl densely, finely ribbed, evolute and depressed:

present (0); absent (1).

3. Umbilical wall initially vertical or overhanging, later sloping:

present (0); absent (1).

4. Strongly dimorphic: present (0); absent (1).

5. Macroconch very large: present (0); absent (1).

6. Non-lappeted microconch: present (0); absent (1).

7. Microconch ribbed throughout ontogeny: present (0); absent

(1).

8. Variocostate macroconch, isocostate microconch: present

(0); absent (1).

9. Degree of involution of macroconch: involute (0); evolute

(1); strongly evolute (2).

10. Inflation of adult whorl: compressed to depressed (0); always

compressed (1).

11. Smoothness of body-chamber in adult macroconch: com-

pletely smooth (0); partially smooth (1).

12. Smoothing of outer whorl starts from: inner flank (0); inner

flank to siphonal part (1); siphonal part (2).

13. Egression of umbilical seam starts from: adult body-chamber

(0); phragmocone (1).

14. Suture: radial (0); radial to protracted (i.e. raised umbilical

saddle envelope) (1); protracted (2).

15. Length of primaries on outer whorl: short (0); long (1).

16. Order of withdrawal of ribbing: primaries first (0); primaries

and seconderies simultaneously (1); secondaries first (2).

17. Withdrawal of ribbing starts from: phragmocone (0); begin-

ning of adult body-chamber (1).

18. Nature of primaries in later ontogeny: straight (0); curved (1).

19. Ventral projection of secondaries in macroconch: absent (0);

present (1).

20. Strength of ribbing in macroconch: fine to coarse (0); fine

(1); coarse (2).

21. Intraspecific variability of macroconch: high (0); low (1).

22. Sex ratio in favour of macroconch: present (0); absent (1).

23. Variocostation of macroconch: weak (0); strong (1); moder-

ate (2).

24. Microconch more evolute: absent (0); present (1).

25. Adult body-chamber length: variable (0); more than three-

quarters of last whorl (1); three-quarters of last whorl (2).

26. Shortening of primaries on adult body-chamber: primaries

absent (0); present (1); absent (2).

27. Persistence of secondaries on adult body-chamber in macro-

conch: secondaries absent (0); up to first quarter (1); up to sec-

ond quarter (2).


1928 Subkossmatia opis (J. de C. Sowerby); Spath, p. 210,

pl. 36, fig. 2; pl. 39, figs 2a–b, 7 [m].

*1928 Subkossmatia obscura Spath, p. 211, pl. 38, fig. 5

[m].

*1928 Subkossmatia coggin-browni Spath, p. 212, pl. 31,

fig. 6; pl. 35, fig. 7; pl. 38, fig. 2; pl. 41, fig. 4a–c

[m].

PLATE 2


1a 1b

2

3a 3b

X

4 X5a

X5b

X 6a 6b 6c

7a7b

X

7c8a X98b

X10

X


*1928 Subkossmatia discoidea Spath, p. 213, pl. 50,

fig. 2a–b [m].

1938 Eucycloceras eucyclum (Waagen); Roman, p. 217,

fig. 29; pl. 19, fig. 204 [M].

1951 Eucycloceras eucyclum (Waagen); Basse and Perro-

don, p. 47, pl. 4, fig. 2a–b [M].

1951 Subkossmatia alfuricoides Basse and Perrodon, p. 49,

pl. 4, fig. 3a–c [m].

1951 Subkossmatia bassei Basse and Perrodon, p. 49,

pl. 3, figs 10a–b, 12; pl. 6, fig. 1a–c [m].

1951 Subkossmatia subfissum Basse and Perrodon, p. 50,

pl. 6, fig. 2a–c [m].

1988 Subkossmatia cf. opis (J. de C. Sowerby); Wester-

mann and Wang, p. 332, pl. 23, figs 8–9 [m].

Nomenclature. Different morphospecies of two previously des-

cribed morphogenera have been combined here. Eucycloceras

retains the generic name, being senior to Subkossmatia in page

priority, but the trivial name opis is the senior objective syno-

nym. Different variants within the microconch are in fact mor-

phospecies in the analytical sense of Linnean taxonomy, but are

here considered to be infrasubspecific units.

Type specimens. The holotype of Ammonite opis Sowerby, 1840

(refigured and designated by Spath 1928, pl. 39, fig. 2a–b as

Subkossmatia opis) from the Callovian of Keera, Kutch, and the

holotype of Stephanoceras eucyclum Waagen, 1875 (GSI Type no.

2020, here refigured in Pl. 1, fig. 1a–c) from the Golden Oolite

of the same locality are considered to be the lectotype and

allotype of the present species, respectively. GSI Type nos. 2023,

16032, 16033, JUM 371 and JUM 505 are designated paralecto-

types.

Diagnosis. Shell compressed except for the inner whorls.

Strongly dimorphic, size ratio c. 2:1, maximum macro-

conch diameter 200 mm, sex ratio c. 1:4 in favour of

microconch. Intraspecific variability is great, especially in

microconchs. Shell with strongly variocostate ribbings,

strong and distant primaries with characteristic adoral

concavity in adult macroconch. Primaries shorten in late

stage in macroconch. Umbilical diameter shows positive

allometry during ontogeny.

A B C D

TEXT -F IG . 9 . Transverse section (body-chamber hatched) of

A, Kamptokephalites lamellosus (Sowerby), B–C, Eucycloceras opis

var. opis, and D, E. opis var. obscura. Note sharp umbilical edge

in inner whorls of both species. All · 0Æ5.

TEXT -F IG . 10 . Growth curves of A, degree of involution and

B, degree of inflation of Eucycloceras opis (J. de C. Sowerby).

TEXT -F IG . 11 . Size distribution of Eucycloceras opis (J. de C.

Sowerby). A, microconch. B, macroconch.


Range. Upper Lower Callovian–lower Middle Callovian.

Material. The present collection includes 137 microconch and

32 macroconch specimens, mostly shell remains. The micro-

conchs JUM 520, 533, 552, 591 come from Bed 8 of Jhura; JUM

373 from Bed 2, JUM 371, 381, 424, 514–515, 517–519, 522–

525, 532, 534, 541 from bed 5 and JUM 245–247, 251, 253, 256–

257, 261, 271, 273–274, 282, 366–367, 370, 372, 374–380, 382–

383, 417, 435 from Bed 6 of Keera; JUM 415, 429 from Bed 8

and 249, 309–310, 384–414, 419–421, 426–427, 432–433, 436–

439, 530, 538–540, 542–547, 549–551, 553–556, 567, 569–578,

580–581, 586, 592 from Bed 9 of Jumara; JUM 423, 531, 535–

537, 568, 579 from Bed 2 and JUM 252, 368, 416, 418, 434 from

Bed 3 of Jara. The macroconchs JUM 459, 505–513, 529, 560–

566 come from Bed 8 of Jhura; JUM 516, 518, 521 from Bed 5

and JUM 428 from Bed 6 of Keera; JUM 422 from Bed 7, JUM

430, 527–528 from Bed 8 and JUM 248, 425, 431, 548 from Bed

9 of Jumara; JUM 369, 557 from Bed 2 of Jara.

Measurements. Deposited on http://palass.org

Description. The species shows wide intraspecific variability

attributed mainly to genetic and ontogenetic factors. It displays

strong allometry during ontogeny. Early stage is represented by

relatively involute, depressed whorls; dense, fine, sharply crested

ribs with short and straight primaries furcating below mid-flank;

vertical umbilical wall with distinct umbilical margin (Text-

fig. 9). Intermediate stage up to end-phragmocone is typified by

evolute, compressed shell. Primary ribs strong and distant but

still sharp; furcation point shifts to above mid-lateral, i.e. prima-

ries become increasingly longer. Adult body-chamber is also

compressed and marked by strongly forwarded, curved with

adoral concavity at middle, blunt and distant primaries; they

gradually attenuate and finally disappear towards peristome; sec-

ondaries continue up to a little distance on body-chamber, then

disappear; umbilical edge rounded with inclined wall; shell more

evolute due to egression of bodywhorl.

Macroconchs generally cover the full ontogenetic pathways

and thus show low variability (Text-fig. 10). Curiously, micro-

conchs vary greatly and their developmental pathways seem to

be affected by heterochrony, especially paedomorphosis. Five dis-

A B

C

E

G

D

F

H

TEXT -F IG . 12 . Matured septal suture of Eucycloceras opis (J. de C. Sowerby). A–B, [m], E. opis var. obscura, redrawn from Spath

1928, pl. 38, fig. 5 and pl. 41, fig. 4c). C–D, [m], E. var opis, lectotype (C), redrawn from Spath 1928, pl. 36, fig. 2. E, E. opis var A. F,

E. opis var discoidea. G–H, [M] (G) allotype, redrawn from Waagen 1875, pl. 35, fig. 1c. E, external lobe; L, lateral lobe; U, umbilical

lobe. All · 1.


tinct variants (infrasubspecies) have been recognized. All the

infrasubspecies are indistinguishable in early stage, but they rep-

resent in their adulthood different growth stages of the total

spectrum of macroconchiate ontogeny. However, none of the

microconchiate variants retains all the features of the species as

evident in macroconchs. They are generally relatively densely

ornate with retention of secondaries to the end of adult body-

chamber.

Microconch. Nucleus whorls remain depressed (B ⁄H ¼ 1Æ2–1Æ5) up to a diameter of about 18 mm, thereafter shell becomes

compressed. Flanks short and gently curved. Venter broad, mod-

erately arched, ventrolateral margin gently rounded. Whorl sec-

tion subcircular to ovate. Umbilicus relatively narrow (U ⁄D ¼0Æ20–0Æ24) with vertical to slightly overhanging wall, umbilical

margin distinct and sharp. Inner whorls are ornamented with

fine, sharp, densely spaced ribs. Primaries originate rursiradiately

from umbilical wall. They pass over flank straight with slight

forward inclination up to ventrolateral margin and cross venter

with further forward bend. Mostly biplicate ribs; however, trifur-

cating ribs and intercalatories are also present. Numbers of pri-

maries and secondaries per half whorl are 18–19 and 40–51,

respectively.

As the shell grows the furcation point shifts from below mid-

lateral to above. At the same time shell becomes compressed and

evolute, at end-phragmocone B ⁄H ¼ 0Æ69–0Æ80, and U ⁄D ¼0Æ24–0Æ33.

Adult shell is always compressed (B ⁄H ¼ 0Æ71–0Æ98), diameter

67–128 mm (Text-fig. 11), adult phragmocone diameter 45–

82 mm. Adult body-chamber occupies three-quarters of last

whorl. Shell egresses rapidly from the regular spiral before

attainment of adult phragmocone, and gives rise to an elliptic

curve of the umbilical seam and becomes more evolute

(U ⁄D ¼ 0Æ30–0Æ38). Adult shell has broad laterals which are flat

to slightly curved. Venter curved to nearly flat. Apertural outline

subtrapezoidal to subelliptical. Sharp umbilical margin with

steep wall continues up to early part of adult body-chamber but

near the last quarter or so umbilical wall becomes gradually slo-

ping and margin gently rounded. Ribbing pattern remains same

as observed in early whorls. Ribs also remain dense, fine and

sharp on adult body-chamber, but become increasingly promin-

ent and slightly distant or may be approximated towards peris-

tome. Ventral arch of secondaries is accentuated towards

aperture.

There exists a co-variation in shell size, coiling, degree of

inflation and ornamentation among the different microconchiate

variants: generally smaller variants are less evolute, compressed,

densely and finely ornate while large variants are more evolute,

inflated, and distantly and coarsely ornate. But, there are excep-

tions.

External lobe deeply incised; external saddle large, broad trifid.

The first lateral lobe less incised, narrow and trifid. The second

lateral lobe much smaller, trifid. U2 still smaller, asymmetric.

Other auxiliary lobes are well developed. Lobes from the first lat-

eral lobe up to the last auxiliary lobe are tied up in a large sad-

dle envelope which shows a little to a conspicuous rise towards

umbilical margin (Text-fig. 12A–E).

The variants within the microconchs generally differ from

each other on the basis of degree of involution and inflation,

and nature of ornamentation as observed on adult bodywhorl.

The following five variants (infrasubspecies) can be distinguished

and some of them are named according to different eucyclocera-

tin species of Spath (1928).

1. E. opis var. A (Pl. 2, figs 4–10). Smallest variant (D ¼67–83 mm, D at end-phragmocone ¼ 45–54 mm); most

compressed (B ⁄H ¼ 0Æ71–0Æ84); relatively less evolute

(U ⁄D ¼ 0Æ30–0Æ34); very densely, finely ornate until the

end (P ¼ 21–29, S ¼ 46–68); rib-crest sharp, symmetrical

in cross-section; ribs always isocostate and show approxi-

mation towards adult aperture. Umbilical wall remains

more or less steep in adult stage, umbilical margin always

prominent and sharp; abundant (32 specimens) but pre-

viously unknown.

2. E. opis var. opis (Pl. 3, figs 6–10). Small (D ¼88–113 mm, D at end-phragmocone ¼ 63Æ5–67 mm);

moderately compressed (B ⁄H ¼ 0Æ76–0Æ89); evolute

(0Æ31–0Æ35); densely, finely ornate (P ¼ 21–29, S ¼ 49–

66). Ribs isocostate, sharp, symmetrical crest; most abun-

dant (49 specimens).

3. E. opis var. obscura (Pl. 4, figs 1–6). Largest variant (D ¼121–128 mm, D at end-phragmocone ¼ 71–82 mm);

weakly compressed (B ⁄H ¼ 0Æ80–0Æ89); most evolute vari-

ant (U ⁄D ¼ 0Æ32–0Æ38); strongly, distantly ornate (P ¼17–27, S ¼ 40–53); ribs isocostate, high-crested, rounded

and asymmetrical with gentler slope towards aperture;

abundant (33 specimens).

4. E. opis var. discoidea (Pl. 3, figs 1–5). Small (D ¼ 77–

97 mm, D at end-phragmocone ¼ 52–70 mm); moder-

ately compressed (B ⁄H ¼ 0Æ75–0Æ89); evolute (U ⁄D ¼0Æ31–0Æ35); distantly ornate (P ¼ 17–18, S ¼ 36–45); ribs

isocostate with angular crest; rare (five specimens).

5. E. opis var. eucyclum (Pl. 5, figs 1–4). Small to medium-

sized (D ¼ 85–115 mm, D at end-phragmocone ¼73 mm); strongly to moderately compressed (B ⁄H ¼0Æ72–0Æ86); least evolute variant (U ⁄D ¼ 0Æ27–0Æ33);


Figs 1–10. Eucycloceras opis (J. de C. Sowerby) [m]. 1–5, var. discoidea. 1a–b, paralectotype, adult with partly preserved body-chamber,

GSI 16033, Smith coll., ‘sub-anceps bed ii’ Smith 1912–15, Ler-Hamundra. 2a–c, adult with partly preserved body-chamber, JUM

252, Bed 3, Jara. 3a–c, adult with partly preserved body-chamber, JUM 391, Bed 9, Jumara. 4a–b, complete adult, JUM 415, Bed

8, Jumara. 5, adult with partly preserved body-chamber, JUM 403, Bed 9, Jumara. 6–10, var. opis. 6a–c, almost complete adult

with broken phragmocone, JUM 388, Bed 9, Jumara. 7, complete adult, JUM 389, ibid. 8a–b, complete adult, JUM 416, Bed 3,

Jara. 9a–c, complete adult, JUM 411, Bed 9, Jumara. 10, complete adult, JUM 378, Bed 6, Keera; note egression of whorl takes

place in phragmocone stage. All · 0Æ5.


primaries broad, blunt, concave forward and fewer in

number (P ¼ 14–20); ribs variocostate, primaries much

stronger than secondaries (S ¼ 49–54) which become

faint to obscure on venter; common (18 specimens).

Macroconch. Shell large, relatively to strongly evolute

(U ⁄D ¼ 0Æ2–0Æ42), compressed (B ⁄H ¼ 0Æ67–0Æ96). Whorl sec-

tion elliptical to subrounded. Maximum adult shell diameter

200 mm, although reconstructed diameter of one specimen

PLATE 3


1a1b

X 2a2b 2c

X

3a 3b 3c

X4a

4b

5

X

X6a 6b 6c

7

8a

X

X

9a 9b 9c 10

X

8b


(JUM 425) appears to be c. 220 mm. Aperture missing; in one

specimen (Pl. 2, fig. 2) presence of dense growth lirae indicates

its almost complete preservation. Adult body-chamber occupies

three-quarters of the last whorl. End-phragmocone diameter

102–135 mm.

Inner whorls up to c. 50 mm in diameter, microconch-like,

barely distinguishable. Laterals gently curved with relatively wide,

broadly arched venter. Shell compressed. Umbilicus relatively

less evolute than microconch at corresponding diameter. Umbil-

ical margin sharp with steep wall. Ribs fine, dense; primaries rise

rursiradiately from umbilical shoulder, straight with forward

projection and furcate below mid-flank; secondaries have the

same forward bend, pass over rounded ventrolateral margin with

a further bend and cross venter with prominent forward projec-

tion. Number of primaries and secondaries on average are 19

and 46, respectively.

After 50 mm diameter up to the end-phragmocone, primaries

become progressively distant, increase in strength but remain

straight and sharp, thus strongly resembling the adult micro-

conch. The furcation point of primaries shifts as observed in the

microconch at a similar growth stage. Umbilical wall becomes

gradually sloping outward, margin narrowly rounded and shell

becomes more evolute. Number of primaries and secondaries

per half penultimate whorl is 16–21 and 51–62, respectively.

From the beginning of adult body-chamber, primaries become

broad, blunt and more distant with pronounced forward concav-

ity whereas secondaries continue up to the first quarter of body-

chamber length before they completely disappear. Subsequently

lengths of primaries shorten as they die out near outer lateral at

about one-third of the flank height from the ventral margin;

thus disappearance of both primaries and secondaries render

ventrolateral and siphonal areas of larger part of adult body-

chamber smooth. Umbilicus appears to be more evolute due to

egression of the seam, thus showing positive allometry and

broadly rounded umbilical margin. Laterals seem to be more

gently curved and venter becomes flattened, as observed in the

largest specimen.

The septal suture of the allotype (¼ Stephanoceras eucyclum

Waagen, 1875 by original designation; refigured here in Text-

fig. 12G), designated here, was described by Waagen (1875) and

reiterated by Spath (1928) and our recent inspection. The septal

suture of the macroconch is similar to that of the microconch;

however, the protracted aspect is less conspicuous in the macro-

conch.

Discussion. The macroconch of Eucycloceras opis has

strongly curved primary ribs on its adult body-chamber, a

feature not shown by Idiocycloceras. The species also dif-

fers in many other characters, as in the comparison

between Eucycloceras and Idiocycloceras that was highligh-

ted in the discussion of the latter.

The microconchs show wide intrasexual variability.

Remarkably, the whole spectrum shows continuous vari-

ation, with only a few exceptions. Failure to recognize

intraspecific variability and sexual dimorphism resulted

in excessive taxonomic splitting by early workers. We

have established that all the small eucycloceratin species

of Spath (1928) are no more than different micro-

conchiate variants of E. opis and most of the infrasub-

species have been named accordingly. Spath’s (1928)

Subkossmatia obscura and S. coggin-browni are so close

that they cannot be differentiated and we have con-

sidered these two species under one infrasubspecies,

obscura.

Callomon (in Donovan et al. 1981) mentioned the

existence of homeomorphism between Macrocephalitinae

and Mayaitinae in every morphological aspect. The pre-

sent eucycloceratin population offers another example of

homeomorphism as in Indonesian macrocephalitin

assemblages (see Westermann and Callomon 1988), but

in this case convergence occurs only in the microconchs.

Basic evolute and compressed shells characterize both

assemblages, thus the Middle Bathonian–Lower Callovian

macrocephalitins of Indonesia are very similar to eucyclo-

ceratins of the Indo-Madagascan Province. Other charac-

ters contributing to wide intraspecific variation within a

species population are remarkably similar. For example,

smaller shells are more compressed and less evolute than

larger ones; compressed shells are finely ornate while

inflated ones have coarse ornamentation; finely and

densely ribbed compressed shells have more projected

secondaries over the venter and a more raised umbilical

suture than their coarsely ornate counterparts. Wester-

mann and Callomon (1988) were confident that individu-

als from two different assemblages or stratigraphic levels

may look alike in isolation, but the overall population

structures vary. In our study, populations are frustratingly

similar, so it is not surprising that earlier workers such as

Spath (1928) and Arkell (1956) did not separate these

heterochronous groups. For example, they synonymized

Indonesian bifurcatus s.s. [m] with Indo-Madagascan Idio-

cycloceras (for details, see Westermann and Callomon

1988). It was Thierry (1978) who returned the Indonesian

forms to Macrocephalites where they were originally


Figs 1–6. Eucycloceras opis (J. de C. Sowerby) var. obscura [m], all adults with body-chamber. 1a–b, paralectotype, almost complete

with inner whorls exposed, GSI 2023, ‘anceps Zone’, Spath 1927–33, Keera. 2a–b, broken body-chamber with inner whorl

exposed, JUM 401, Bed 9, Jumara. 3a–c, paralectotype, GSI 16032, ‘sub-anceps beds’, Smith Coll. 1912–15, probably from Habye.

4a–b, JUM 545, Bed 9, Jumara. 5a–b, JUM 384, ibid. 6a–c, JUM 402, ibid. All · 0Æ5.


placed by Boehm (1912). Thierry, however, considered

that many of Spath’s (1928) Indonesian species (e.g.

forms ‘transitional to eucycloceratids’, ‘E. intermedium’

and ‘I. bifurcatum’) were geographical variants of M. sub-

trapezinus (Waagen) (¼ K. lamellosus of Spath 1928)

from Kutch, and Westermann and Callomon (1988) cor-

rectly pointed out differences in their degree of involution

and inflation. Repeated misidentifications have resulted in

1a 1b

X2a 2b

X3a 3b 3c

X 4a 4b

5aX

5b 6a

X6b

6c


PLATE 4


a notion of strong homeomorphism not only between

microconch bifurcatus s.s. and eucycloceratin microconchs

but also between the latter and the microconchiate sub-

compressus group of species. Due to the finite range of

shell coiling and functional constraints (Kennedy and

Cobban 1976) ammonites often developed similar forms

within monophyletic or unrelated groups. The conver-

gence of related groups is compounded if their stratigra-

phy is not adequately known. In their seminal paper

Westermann and Callomon (1988) separated the older

Indonesian forms (Middle Bathonian–Lower Callovian)

from the younger (Middle Callovian) descendant

stock (Eucycloceratinae) using subtle morphological dif-

ferences.

The neotype of M. bifurcatus trans. intermedius

(Westermann and Callomon 1988, pl. 7, fig. 1a–d) is clo-

sely comparable with our E. opis var. obscura [m]. M. keeu-

wensis, especially var. B [m] (Westermann and Callomon

1988, pl. 13, figs 1–2), on the other hand, strongly resem-

bles E. opis var. opis [m]. Westermann and Callomon

(1988) distinguished Indonesian forms, e.g. M. keeuwensis

var. B [m], by their sharp umbilical margin and dense and

sharp ribbing on the body-chamber. Abundant specimens

of the microconch of E. opis are now available. The popu-

lation structure encompasses the whole range of variability

of M. keeuwensis. In E. opis var. A the umbilical edge

remains sharp in the body-chamber. More sharp primary

ribs are present in var. A and var. opis. However, our

microconchs are more evolute and the degree of inflation

shows a wider range of variation. Westermann and Callo-

mon (1988) correctly noted that egression of whorls takes

place in the body-chamber of Indonesian microconchs

whereas it begins early in ‘Subkossmatia’. They wrongly

mentioned, however, that the holotype of ‘S. opis’ is fully

septate and still shows egression. Spath (1928, pl. 39,

fig. 2a) clearly showed the position of the adult end-

phragmocone which suggests that at least two-thirds of the

outer whorl represents the body-chamber. However, egres-

sion still occurs from the septate stage.

Close examination reveals that these two populations,

however, differ quantitatively in some characters. For

example, Eucycloceratinae are more evolute than Indo-

nesian macrocephalitins, as already mentioned, and they

constitute the most evolute forms within the family. Sec-

ondly, they have longer primaries in the outer whorl

and secondaries disappear from the body-chamber

instead of primaries, which are seen in macrocephalitin

macroconchs. Thirdly, egression of the umbilical seam in

Eucycloceratinae takes place from the phragmocone

stage. Finally, the nature of dimorphism completely sep-

arates the two assemblages. Eucycloceratin macroconchs

are quite different in appearance: they are evolute and

dominantly compressed.

The microconchs of Eucycloceras opis, especially var.

A and var. opis, closely resemble Dolikephalites subcom-

pressus. Their nucleus whorls are depressed and barely

distinguishable. E. opis var. A [m] resembles the interme-

diate stage of D. subcompressus in retaining the fine, dense

ribbing while E. opis var. opis resembles the outer whorl.

Morphometrically D. subcompressus and E. opis var. opis

[m] show similar allometric changes during ontogeny in

degree of inflation and involution (personal data based

on numerous topotypes of D. subcompressus); however,

var. opis is more evolute and compressed. Morphologi-

cally fine, dense secondaries with ventral projection char-

acterize both species. D. subcompressus has shorter

primaries throughout ontogeny while this feature is seen

in the early ontogeny of E. opis var. opis. Both species are

characterized by having a prominent umbilical margin

with a steep wall during early stages, which gives way to

sloping wall with rounded margin in adult whorls. E. opis

var. opis retains a sharp umbilical edge for a longer onto-

geny (see Text-fig. 9B–C) and in E. opis var. A it

continues to the end (see Pl. 2, fig. 7c). In Kutch, D. sub-

compressus ranges from the Lower Callovian and E. opis

ranges from the uppermost Lower Callovian–lower Mid-

dle Callovian.

Eucycloceratinae occurs predominantly in the Indo-

Madagascan region and is most abundant in Kutch. There

are, however, reports of their occurrences from the Hima-

layan region and Madagascar. Spath (1928) described

Subkossmatia flemingi (pl. 38, fig. 1a–c) from the doubtful

Callovian horizon of the Salt Range, Pakistan, on the

basis of a fragmented specimen with incompletely pre-

served body-chamber. It is evolute, larger and has coarse

ornamention, and thus may come close to our E. opis

var. obscura. However, based on his description it appears

that it has a smooth venter in the later stage with a roun-


Figs 1–4. Eucycloceras opis (J. de C. Sowerby) var. eucyclum [m], all adults with body-chamber. 1, JUM 424, Bed 5, Keera. 2a–c, nearly

complete, JUM 423, Bed 2, Jara. 3a–c, complete, JUM 517, Bed 5, Keera. 4a–b, complete, JUM 535, Bed 2, Jara. Note concave

primaries, variocostate ribbing in all lateral views and faint to obsolete secondaries in ventral views.

Figs 5–7. Idiocycloceras perisphinctoides Spath [m]. 5a–b, partly preserved bodywhorl with slightly depressed nucleus whorl, JUM 559,

Bed 3, Jara. 6a–c, complete adult, JUM 296, Bed 9, Jumara. 7, nearly complete adult, JUM 449, Bed 8, Jhura.

All · 0Æ5.


ded whorl section. Spath did not provide a ventral view

and we cannot determine whether this smoothness is bio-

logical or due to abrasion of the test. Its affinity is there-

fore uncertain.

Basse and Perrodon (1951) described three new spe-

cies of Subkossmatia from Madagascar. Among them, the

affinity of S. bassei and S. alfuricoides with the present

microconch is certain, but the population structure of


PLATE 5

X1

2a X 2b 2c

3a X 3b 3c

X4a

4b

5a 5b

6a 6b 6c X7

X


Madagascar is slightly different. They are relatively coar-

sely and distantly ribbed even in the smaller adult vari-

ant and relatively less evolute. This may be attributed to

geographical variation or small sample size (only three

specimens).

S. bassei (Basse and Perrodon, 1951, pl. 3, figs 10a–b,

12; pl. 6, fig. 6a–c) is a monotypic holotype and is an

almost completely preserved full-grown specimen. Its

sharp, isocostate ribbing, relatively steeper umbilical wall,

degree of inflation and size make it an intermediate

form between the two variants, opis and obscura. The

sharply crested ribs on the body-chamber and degree of

involution bring it close to opis whereas its less densely

ribbed ornamentation and relatively larger size place it

near obscura.

S. alfuricoides (ibid., pl. 4, fig. 3a–c) appears to be a

nearly complete adult shell and matches well with E. opis

var. opis in adult size and ornamentation but it is less

evolute on the body-chamber.

S. subfissum (ibid., pl. 6, fig. 2a–c) is difficult to corre-

late because the measurements provided do not tally with

the magnification provided for the plate. If the text meas-

urements are correct, it is a large form with coarser rib-

bing. It resembles our E. opis var. obscura.

Genus IDIOCYCLOCERAS Spath, 1928

Type species. Idiocycloceras perisphinctoides Spath, 1928.

Idiocycloceras perisphinctoides Spath (1928)

Plate 5, figures 5–7; Plates 6–10; Text-figures 13–18

*1875 Stephanoceras fissum (non Sowerby); Waagen,

p. 134, pl. 37, figs la–b only [M].

1894 Macrocephalites fissus (Waagen); Tornquist, p. 14,

18–19 [M].

1910 Macrocephalites fissus (Waagen); Uhlig, p. 265 [M].

1910 Macrocephalites fissus (Waagen); Lemoine, p. 22,

text-fig. 35, pp. 24, 37 (non p. 29) [M].

1913 Stephanoceras fissum (Waagen); Smith, b, p. 420; c,

p. 423 [M].

1914 Macrocephalites fissus (Waagen); R. Douville,

pp. 362–363 [M].

1928 Subkossmatia ramosa Spath, p. 214, pl. 39, fig. 1;

pl. 41, fig. 1a–b [M].

1928 Subkossmatia sp. ind. Spath, p. 215, pl. 3, fig. 1a–b

[M].

*1928 Idiocycloceras perisphinctoides Spath, p. 215, pl. 36,

fig. 3; pl. 38, fig. 3a–c [M].

*1928 Idiocycloceras singulare Spath, p. 216, pl. 28, fig. 8;

pl. 40, fig. 5; pl. 41, fig. 2 [M].

*1928 Idiocycloceras dubium Spath, p. 217, pl. 39, fig. 6a–

b [M].

1928 Idiocycloceras sp. ind. Spath, p. 218, pl. 35, fig. 6;

pl. 41, fig. 3 [M].

1933 Idiocycloceras singulare Spath, pl. 129, fig. 8; pl. 130,

fig. 8 [M].

non1951 Idiocycloceras Spath sp. ind.?; Basse and Perrodon,

p. 51, pl. 5, fig. 5a–b.

Nomenclature. Spath’s (1928) Idiocycloceras perisphinctoides,

I. singulare and I. dubium are combined here into a single spe-

cies and the name I. perisphinctoides, which is the senior subject-

ive synonym, is retained. Two larger Subkossmatia species of

Spath (1928) (S. ramosa and S. sp. indet.) are also considered to

be conspecific. S. ramosa has page priority over I. perisphincto-

ides, but the more familiar name of the type species is upheld.

Type specimens. Waagen’s (1875) ‘Stephanoceras fissum’ (GSI

Type no. 2029) was considered by Spath (1928) to be the holotype

of his Idiocycloceras singulare. The specimen is an adult shell with

a partly preserved body-chamber. The holotype of I. perisphincto-

ides is an immature specimen. We have, therefore, redesignated

the former as the lectotype of the present species and it is repro-

duced photographically for the first time (Pl. 9, fig. 1a–c). GSI

type nos. 16036, 16038, JUM 327, 489 are considered to be

paralectotypes.

Diagnosis. Shell strongly evolute, macroconch being the

most evolute within the family. Whorl shape variable,

ranging from depressed to compressed in adult whorl.

Shell very large, maximum diameter being 270 mm.

Dimorphic size ratio c. 2Æ5:1 and sex ratio c. 7:1 in favour

of macroconch. Shell coarsely ornate, mostly biplicate and

weakly isocostate. Primaries distant, blunt and straight

on adult body-chamber and finally die out near the

peristome. Secondaries continue up to half of adult body-

chamber length. Degree of involution shows negative

allometry in macroconch which becomes less evolute in

adult stage.


Figs 1–9. Idiocycloceras perisphinctoides Spath. 1a–c, [m], complete adult, JUM 270, Bed 6, Keera. 2, [m], complete adult, JUM 272,

ibid. 3a–c, [m], adult with partly preserved body-chamber, JUM 260, ibid. 4a–b, [m], adult with partly preserved body-chamber,

JUM 503, Bed 9, Jumara. 5a–c, [M], septate inner whorl with partly preserved body-chamber, JUM 440, Bed 3, Jara. 6, [M],

wholly septate inner whorl, JUM 538, Bed 8, Jumara; note deep crateriform umbilicus in nucleus whorl. 7a–c, [m], inner whorls,

JUM 526, Bed 8, Jhura. 8a–b, [M], wholly septate phragmocone, JUM 295, Bed 9, Jumara. 9a–b, [M], wholly septate

phragmocone, JUM 297, ibid. All · 0Æ5.


Occurrence. Lower Middle Callovian.

Material. The present collection includes 155 macroconch and

28 microconch specimens. The macroconchs JUM 277, 288, 290,

292–293, 349, 444, 450–451, 456, 458, 460, 462–468, 471–474,

481, 483, 500 come from Bed 8 of Jhura; JUM 243, 442, 461,

470, 490, 501, 582, 589 from Bed 5 and JUM 241–242, 250, 255,

259, 264–269, 275, 278–281, 283–285, 287, 289, 291, 453 from

JANA et al., Idiocycloceras

X

1a 1b 1cX

2

X3a 3b 3c

4a 4b

5a 5b 5c 6

7a

7b 7c

8a 8b 9a9b

PLATE 6


Bed 6 of Keera; JUM 319, 337, 361, 477, 487, 583 from Bed 8

and JUM 263, 276, 295, 297–305, 307–308, 311–313, 315–318,

320–322, 324–326, 339–342, 344–348, 350–351, 353, 355–360,

365, 454–455, 475–476, 478–480, 482, 485–486, 488–489, 491–

495, 497, 584–586, 590 from Bed 9 of Jumara; JUM 447–448,

452, 469, 496, 498 from Bed 2 and JUM 338, 440–441, 443,

445–446, 457, 484 from Bed 3 of Jara. The microconchs JUM

449, 502, 526 come from Bed 8 of Jhura; JUM 504 from Bed 5

and JUM 244, 254, 258, 260, 262, 270, 272, 323, 354 from Bed 6

of Keera; JUM 286, 294, 296, 306, 314, 327, 343, 352, 362–363,

503, 587 from Bed 9 of Jumara; JUM 558 from Bed 2 and JUM

364, 559 from Bed 3 of Jara.

Measurements. Deposited on http://palass.org

Description

Macroconch. The population shows high intraspecific variability.

Shell moderately to strongly evolute (U ⁄D ¼ 0Æ27–0Æ46), highlycompressed to strongly depressed (B ⁄H ¼ 0Æ74–1Æ84). Whorl out-

line subtrapezoidal to ovate. Shell very large, maximum adult

diameter being 270 mm. One adult body whorl fragment (JUM

365) appears to be a smaller variant with reconstructed diameter

of about 180 mm. The largest specimen (JUM 489, Pl. 12, fig. 1a)

with peristome preserved, shows dense growth striae near aper-

ture. Adult phragmocone diameter ranges from 135 to 192 mm.

Adult body-chamber occupies three-quarters of the last whorl.

Degree of inflation shows strong allometry during ontogeny

(Text-fig. 14). Inner whorls remain depressed at least up to a

diameter of about 50 mm. However, nucleus whorls are very

depressed (at 17 mm, B ⁄H ¼ 1Æ83; at 50 mm, B ⁄H ¼ 1Æ05–1Æ35). Flanks short, strongly curved; wide, gently arched venter

with gradual ventrolateral margin. After 50 mm diameter some

variants develop compressed whorl (B ⁄H ¼ 0Æ74–0Æ95) and

remain compressed to the end. Other variants also develop a

compressed whorl, show maximum compression at end-

phragmocone (B ⁄H ¼ 0Æ83–0Æ97), thereafter again become

depressed (B ⁄H ¼ 1Æ03–1Æ10). However, difficulties lie in separ-

ating them into two morphs because of the fact that there are

specimens that remain depressed throughout. The population

exhibits an overall decrease of B ⁄H ratio during ontogeny (neg-

ative allometry). On outer whorl, flanks may be broad, curved

to flattened. Venter with variable width and curvature. Ventro-

lateral margin gently rounded.

Umbilicus large, perisphinctoid to crateriform. There is a weak

correlation between whorl shape and nature of umbilicus, i.e.

compressed (B ⁄H c. 0Æ9) shells have evolute, perisphinctoid-type

shallow umbilicus (U ⁄D c. 0Æ4) while tumid variants with strongly

curved flanks (B ⁄H c. 1Æ35) are associated with relatively small,

deep, crateriform umbilicus (U ⁄D c. 0Æ28). Again, intermediates

exist. Degree of involution also shows allometry (Text-fig. 14). It

increases up to the end-phragmocone stage, and thereafter decrea-

ses. Umbilical wall is steep in early ontogeny and subsequently

tends to become inclined. Umbilical edge is sharp and distinct in

early stage, becomes gradually rounded during ontogeny.

Shell is strongly ornate, mostly biplicate and weakly varioco-

state. There is also a co-variation between degree of inflation

and strength of ribbing, i.e. ornamentation in inflated variants

is relatively stronger than that in compressed variants. Inner

whorls up to a diameter of about 40 mm are, however, orna-

mented with fine, sharp and moderately dense ribs. Primaries

originate rursiradiately from unbilical wall and are straight with

a slight forward inclination over flanks. Primaries are divided

into two branches. However, the position of furcation changes

during ontogeny. In early whorls, bifurcation takes place below

mid-lateral. At about 75 mm diameter bifurcation takes place

nearly at mid-flank, thereafter primaries become longer and

split at about two-fifths whorl height from the ventral margin.

Secondaries have the same forward projection up to ventrolat-

eral margin from where they are much more projected forward

across venter. Both primaries and secondaries sharply crested,

raised and asymmetric with gentler slope towards aperture up

to end-phragmocone stage. Primaries become progressively dis-

tant and blunt on adult body-chamber and near the last quar-

ter of body whorl they may become curved with slight adoral

TEXT -F IG . 13 . Size distribution of Idiocycloceras

perisphinctoides Spath. A, microconch. B, macroconch.


Figs 1–4. Idiocycloceras perisphinctoides Spath, [M]. 1a–c, paralectotype, wholly septate phragmocone, GSI 16038, ‘sub-anceps beds’,

Smith Coll. 1912–15, Ler-Hamundra. 2a–c, adult with partly preserved body-chamber, GSI 16035, ‘sub-anceps beds’, Smith Coll.

1912–15, Keera. 3a–c, paralectotype, immature phragmocone with partly preserved body-chamber, GSI 16036, ‘sub-anceps beds’,

Smith Coll. 1912–15, Habye. 4, smooth venter of an adult body-chamber, JUM 450, Bed 8, Jhura. All · 0Æ5.


concavity. Their strength attenuates, and they become flattened

to obsolete and finally die out leaving the peristome smooth,

but with dense growth striae. Ventral projection of secondaries

increases up to penultimate whorl. Secondaries continue

beyond adult phragmocone end, tend to be blunt and obsolete

first in venter, finally disappearing at about half of body-cham-

ber length rendering the siphonal and ventrolateral region of

the test smooth.


1a1b 1c

2a

X

3a

3b 3c2b

2c 4

PLATE 7


The general pattern of septal sutures is projected towards

umbilicus with a broad typical saddle envelope of lobes like that

of Eucycloceras (Text-fig. 15). Umbilical projection and degree of

incision are variable. First lateral lobe is relatively larger, strongly

trifid and slightly asymmetric; second lateral lobe and auxiliary

lobes are distinctly developed.

Microconch. Microconchs resemble intermediate stage of

macroconch in many ways. Microconch population shows more

or less similar range of variation in degree of involution

(U ⁄D ¼ 0Æ32–0Æ44) and inflation (B ⁄H ¼ 0Æ8–1Æ18), but they

are less evolute and less depressed than macroconchs. Adult

whorl outline subtrapezoidal to subrounded (Text-fig. 16). Adult

shell diameter ranges from 93 to 131 mm; adult phragmocone

diameter is about 70 mm. Adult body-chamber occupies three-

quarters of the last whorl.

Inner whorls are indistinguishable from those of macroconch;

both are depressed and less evolute. However, in microconch,

depression continues up to 18 mm diameter. Degree of inflation

shows allometry similar to that of macroconch with increase in

shell diameter.

Umbilicus relatively large, shallow to moderately deep. Initial

vertical umbilical wall becomes inclined later, and margin, sharp

and distinct in early stages, becomes rounded in last stage.

Co-variation between degree of involution and degree of infla-

tion as observed in macroconch, however, is not evident, per-

haps because the growth of umbilicus does not replicate the

whole macroconch ontogeny and the degree of involution

resembles late to end-phragmocone stage of macroconch.

Ribbing pattern is similar to that of macroconch. Ribs are

fine, sharp and dense up to a diameter of about 50 mm. Adult

whorl is strongly, distantly ornate. Both primaries and secondar-

ies become blunt, rounded. Adoral convexity of secondaries over

venter becomes pronounced in the last quarter of the body-

whorl. Approximation of ribs takes place near peristome.

Septal sutures not clearly discernible.

Discussion. Idiocycloceras is the most evolute genus of all

the sphaeroceratids. It differs from Eucycloceras in having

a larger shell, more evolute whorl and coarser ornamenta-

tion. In the adult stage of Eucycloceras [M] primaries

become strongly curved, but in the same growth stage of

Idiocycloceras [M] primaries show little curvature. The

adult whorl section of Idiocycloceras is highly variable,

may be depressed; but the adult whorl of Eucycloceras is

always compressed. In the Idiocycloceras population the

sex ratio strongly favours the macroconch (M:m c. 7:1),

whereas the reverse trend is reflected in Eucycloceras pop-

ulation (M:m c. 1:4). The dimorphic size ratio (M:m) in

Idiocycloceras is approximately 2Æ5:1, whereas in Eucycloc-

eras it is 2:1.

Idiocycloceras bifurcatum reported by Spath (1928,

p. 206) from the Bathonian of Sula Island, Indonesia, was

incorrectly identified. Westermann and Callomon (1988)

re-identified it as a microconch of Macrocephalites bifurc-

atus s.s. It closely resembles the microconch of the present

species. They are comparable in degree of involution and

coarse ornamention. The adult size of M. bifurcates [m]

is 70–90 mm whereas that of I. perisphinctoides [m] is

93–131 mm. Moreover, in M. bifurcatus s.s. [m] primaries

bifurcate just below or at mid-flank at all growth stages, a

typical macrocephalitin character, but in I. perisphincto-

ides [m] they bifurcate above mid-flank at a later stage.

The microconch of the present species closely resembles

E. opis var. obscura [m], but I. perisphinctoides [m] is

coarser and is more evolute.

Basse and Perrodon (1951, pl. 5, fig. 5a–b) described a

specimen from Madagascar as Idiocycloceras sp. indet.

From their figure and description the specimen appears

to belong to Kamptokephalites. Collignon (1958, pl. 21,

fig. 86) illustrated, but did not describe, a specimen from

the upper Lower Callovian of Madagascar as Idiocycloceras

rebellyi. The specimen is a small evolute form with

depressed whorls and coarse ornamantion. Westermann

and Wang (1988) were unable to locate this specimen in

the Collignon (Dijon) and Rebelli (Paris) collections.

They doubtfully included it in their synonymy list of

Grayiceras? gucuoi (pl. 24, figs 7–14; text-fig. 12C–E) from

TEXT -F IG . 14 . Growth curves of A, degree of involution and

B, degree of inflation of Idiocycloceras perisphinctoides Spath.


Figs 1–2. Idiocycloceras perisphinctoides Spath [M], adults with partly preserved body-chamber and broken phragmocone. 1a–b, JUM

333, Bed 9, Jumara. 2a–b, specimen shown in Plate 7, figure 4. All · 0Æ5.


the Callovian of Tibet, which strongly resembles the

microconch of I. perisphinctoides.

Westermann and Wang (1988) suggested that the holo-

type of Idiocycloceras perisphinctoides is probably a micro-

conch and its supposed macroconch is I. singulare. We

have inspected both of the type specimens and noted

that I. perisphinctoides is a septate macroconch. They also


1a

X

1b

2a

X

2b

PLATE 8


concluded (p. 331) that Idiocycloceras has a ‘trapezoidal,

rather than elliptical to subovate, and more compressed

section of the inner whorls.’ However, the inner whorls of

Idiocycloceras, which are up to 50 mm in diameter, are

always depressed (Text-fig. 16B–C).

DISCUSSION

Eucycloceratinae occupy an intermediate position between

the Macrocephalitinae and Mayaitinae (Text-fig. 8B).

Most workers consider that they constitute an evolution-

ary plexus, but the fossil record is marked by a great hia-

tus between the Eucycloceratinae and Mayaitinae

(comprising the entire Upper Callovian) (see Donovan

et al. 1981). Eucycloceratinae not only cryptically

A

C

E

B

D

TEXT -F IG . 15 . Septal sutures of Idiocycloceras

perisphinctoides Spath, [M]. A–B and D–E, redrawn

from Spath 1928, pl. 36, fig. 3; pl. 41, fig. 3; pl. 28,

fig. 8; and pl. 41, fig. 2, respectively. C, drawn from a

internal mould of a topotype (JUM 241). All · 1.

A B C

TEXT -F IG . 16 . Transverse sections (body-chamber hatched) of

A, Dolikephalites subcompressus (Waagen) and B–C, microconchs

of Idiocycloceras perisphinctoides Spath. Note sharp umbilical

edge and steep wall of inner whorls of D. subcompressus and

phragmocone of I. perisphinctoides. All · 0.5.


Figs 1–2. Idiocycloceras perisphinctoides Spath [M], adults with partly preserved body-chamber. 1a–c, lectotype, GSI 2029, Keera,

photographically presented for the first time. 2a–c, paralectotype, GSI 16037, ‘sub-anceps beds II’, Smith Coll. 1912–15, Ler-

Hamundra. All · 0Æ5.


appeared in the Indo-Madagascan region during the latest

Early Callovian, but flourished and diversified producing

the new genus Idiocycloceras, and then disappeared

equally suddenly during the early Middle Callovian. The

entire history of the subfamily spans less than the dur-

ation of a standard zone. Did they become extinct or

were they ecologically excluded? How did they acquire

novelties such as a protracted suture and an evolute,

compressed shell that their immediate macrocephalitin

ancestor in Kutch lack?


1a

X

1b 1c

X

2a2b

2c

PLATE 9


The monographic treatment of Macrocephalites assem-

blages of south-west Pacific Indonesia (Westermann and

Callomon 1988) indicates that these oldest macrocephali-

tins show wide interspecific diversity, which was not

revealed by their younger Tethyan counterparts of both

Europe and the Indo-Madagascan region. The macro-

conchiate bauplan, however, shows low diversity and

remains conservative throughout the range of the sub-

family, while the microconchs show great phenotypic vari-

ation with respect to whorl inflation, degree of involution,

nature of ornamentation and, more importantly, septal su-

tural patterns. There may be strong to weak correlations

among these features which result in a plethora of forms

characterizing monospecific or successive assemblages.

Generally microconchiate forms are compressed and evo-

lute. There is a good correlation between forms having

dense, fine ribbing with projected secondaries over the

adult venter and possession of a raised umbilical saddle.

This correlation transcends taxonomic boundary and is

found in many species, e.g. M. bifurcatus [m] and

M. keeuwensis [m], especially var. B. This latter variant is

strongly compressed and evolute with ‘unusually high

(‘‘raised’’) umbilical saddles’ (see Westermann and Callo-

mon 1988, p. 69), thus resembling a ‘Subkossmatia’-like

microconch, e.g. our E. opis var. opis [m]. This homeo-

morphism created confusion for many early workers such

as Spath (1928) and Arkell (1956). Westermann and

Callomon (1988) provided the requisite stratigraphical

data and resolved the issue. These ancestral Indonesian

forms presumably migrated to the Tethys Ocean during

the Late Bathonian, which Callomon (1993) described as a

‘bio-event par excellence’. Upper Bathonian records of

both the European and the Indo-Madagascan areas wit-

nessed the cryptic appearance of Macrocephalites (Dietl

1981; Dietl and Callomon 1988; Datta et al. 1996) and not

at the base of the Callovian as previously thought (e.g.

Donovan et al. 1981). This evolutionary pattern in the

Tethyan region can be linked with the global marine trans-

gression at the start of the Callovian (Hallam 1981; Haq

et al. 1987). We speculate that during this migrational

event not all of the species participated. It may be sheer

chance that only involute, inflated forms with a radial

suture invaded the Tethyan area and subsequently diversi-

fied.

Subsequently, macrocephalitin evolutionary history

continued in two main biogeographical areas: European

Tethys and the Indo-Madagascan Province. It has gener-

ally been considered that they constituted two distinct

provinces, and macrocephalitin species in these had dif-

ferent modes of diversification (cf. Krishna and Cariou

1993), perhaps following vicariance biogeographical mod-

els (see Grande 1996). Occasionally, however, authors

have attempted to compare and synonymize contempora-

neous species of the two areas. For example, Westermann

and Callomon (1988) mentioned their close resemblance

and Krishna and Cariou (1993) found ‘undeniable simi-

larity’ between M. triangularis and M. jaquoti, although

Callomon et al. (1989) and Datta et al. (1996) had reser-

vations. M. jaquoti is the oldest macrocephalitin species

from the Lower Callovian of Europe and is slightly

younger than M. triangularis from the Upper Bathonian

of the Indo-Madagascan region (Datta et al. 1996). The

next youngest species, but still within the Indo-Madaga-

scan Upper Bathonian, is M. madagascariensis. It closely

corresponds to M. verus, which occupies a stratigraphical-

ly higher level than M. jaquoti in the Sub-Mediterranean

Western Tethys (Westermann and Callomon 1988;

Krishna and Cariou 1993). Likewise M. macrocephalus

(Schlotheim) appears to be very similar in grade of

organization (e.g. see Thierry 1978, pl. 9, figs 1–2) to the

contemporaneous M. formosus from the Indo-Madagascan

Faunal Province: both are similar in size and whorl-out-

line, and in having a smooth body-chamber. However,

some variants of the European species (e.g. Thierry 1978,

pl. 8, fig. 2a–b) have traces of weak secondaries restricted

to the adult venter, and the inner whorls of both species

are somewhat different (see also Westermann and Callo-

mon 1988; Bhaumik et al. 1993). Datta et al. (1996) found

similarities between M. formosus and M. cannizaroi. Both

show an early disappearance of primary ribs. Callomon

(1971) reiterated Spath’s (1927–33) view that the M. for-

mosus-M. madagascariensis group is the Indian equivalent

of M. macrocephalus (Schlotheim). The uppermost level

of the Lower Callovian in the Indo-Madagascan region

yields an endemic genus, Nothocephalites, marking the

highest subzone and faunal horizon. Significantly, at

a similar stratigraphical level in Europe, the species

M. gracilis appears, which is closely comparable to Notho-

cephalites (Westermann and Callomon 1988, p. 16). There

are also reports of faunal homogeneity of other species

between Kutch and Sub-Mediterranean France:

Indocephalites transitorius, I. kheraensis, I. chrysoolithicus,

Kamptokephalites lamellosus and K. dimerus are common

elements (Thierry 1978; Cariou 1984). Thus it appears

that the dominant macrocephalitin species of both geo-

graphical areas show a broad morphological homogeneity


Figs 1–3. Idiocycloceras perisphinctoides Spath [M]. 1a–c, adult with partly preserved body-chamber, JUM 331, Bed 9, Jumara. 2a–b,

adult body-whorl fragment of a small variant showing smooth venter, JUM 365, Bed 9, Jumara. 3a–b, adult with partly preserved

body-chamber, JUM 460, Bed 8, Jhura. All · 0Æ5.


and ‘parallel’ trends in evolution. Moreover, the micro-

conchiate forms (recognized in the Kamptokephalites-

Dolikephalites group of species) of both Europe and the

Indo-Madagascan region are remarkably similar (Thierry

1978; Westermann and Callomon 1988). Contrary to the

hypothesis of development of independent successions

(cf. Krishna and Cariou 1993) we believe that faunal simi-

larities speak for rapid migrational events and suggest the


PLATE 10

1a

X1b 1c

2a

X

3a 2b 3b


existence of a well-established sea connection between

these two areas.

The Kamptokephalites-Dolikephalites group of species

has a considerable range in Kutch from the Lower Callo-

vian to the base of the Middle Callovian (Spath 1927–33;

pers. obs.), and thus have stratigraphical overlap with

eucycloceratins. Interestingly this group also extends up

to the lower Middle Callovian in Europe (Cariou 1984).

The younger transients in Kutch, however, show some

interesting developments. For example, ‘Stephanoceras

subtrapezinum’ Waagen (included in the synonymy list of

Kamptokephalites lamellosus by Spath 1928) and ‘Stepha-

noceras subcompressum’ Waagen (¼ Dolikephalites subcom-

pressus of Spath 1928) have a somewhat raised umbilical

saddle, as noted by Waagen (1875, pp. 138–139) and con-

firmed by our recent inspection of the specimens (GSI

nos. 2016 and 2018, respectively). We have already men-

tioned, as evident from the older macrocephalitins from

Indonesia, that there possibly exists a correlation between

a rise in umbilical saddle, fineness of ornamentation and

a compressed, evolute shell. It is possible that these chan-

ges relate to mutation in a pleiotropic gene (i.e. a single

gene that is responsible for a number of different pheno-

typic effects that are apparently unrelated). A mutation in

the younger transients of the K. lamellosus-D. subcompres-

sus group of species may have changed the nature of the

sutural pattern from radial to protracted. Later a similar

mutation may have resulted in complete differentiation of

a new stock, i.e. Eucycloceratinae, which are very similar

to the evolute Indonesian species. It now seems likely that

the eucycloceratin microconchs are heterochronous

homeomorphs of these older Indonesian microconchs (cf.

Westermann and Callomon 1988). Recurrence of homeo-

morphy is widespread in the stratigraphical record of fos-

sils. The innovation of the raised umbilical suture in the

older macrocephalitins of Indonesia during the Mid-

dle Bathonian, its disappearance in the species of late

macrocephalitin phylogeny, i.e. Late Bathonian–Early

Callovian stocks of Europe and Indo-Madagascan area,

and its reappearance in the eucycloceratin descendants

during the Middle Callovian, may be explained by a gen-

etic phenomenon. Like the development of the raised

umbilical suture, the virgatotome ribbing style is another

morphological innovation that appeared time and again

in the phylogeny of the Late Jurassic family Ataxiocerati-

dae, resulting in widespread homeomorphy. Callomon (in

Donovan et al. 1981, p. 127) explained the recurrence of

this feature as ‘the expression of a single gene that oscilla-

ted between dominant and recessive’. Callomon’s specula-

tion is now supported by some recent studies in

developmental biology, especially epigenetics, which sug-

gests that certain ‘sites’ in the genome of the developing

embryo evidently retain a dormant capacity to produce

features believed to have been lost during evolution. It is

now thought that genes are ‘switched off ’ due to altered

epigenetic pathways and may reappear in subsequent phy-

logeny, thus showing parallel and convergent evolution

(Fahræus 1987).

Nothocephalites, which is coeval with the older eucyclo-

ceratins of the late Early Callovian, was perhaps also

affected by a muted gene and is characterized by posses-

sing a raised umbilical saddle envelope (Spath 1928).

Krishna and Westermann (1987), however, mentioned

(also supported by our observations) that this is present

only in N. asaphus. The type specimen of N. semilaevis is

fully septate while that of N. asaphus has an incomplete

body-chamber. These two species are strictly contempora-

neous and were originally based on monotypic holotypes.

We have many adult specimens of both species which

show that N. asaphus is smaller and replicates intermedi-

ate-sized N. semilaevis, and their inner whorls are barely

distinguishable. Thus we strongly believe that N. asaphus

is a microconch (details will be published elsewhere).

However, Nothocephalites was short-lived. The effect of

initial mutation made significant phenotypic changes

since ornamentation became fine and dense and nucleus

whorls are indistinguishable from M. keeuwensis var. B

[m] and our E. opis var. opis [m], as noted by Spath

(1928) and Westermann and Callomon (1988). We have

already mentioned that we prefer to retain Nothocephalites

within the macrocephalitin clade since it is not suffi-

ciently differentiated in the eucycloceratin way. This is

also supported by the cladistic analyses reported herein. It

is worth noting that the raised nature of the umbilical

suture either appeared first, or became more prominent,

in the microconch in macrocephalitin phylogenetic

history, and finally played a major role in the evolution

of the eucycloceratin lineage. Here we must acknowledge

Spath (1924, 1927–33), who correctly envisaged that the

Eucyocloceras-Subkossmatia group owed its origin to the

subcompressus group of Dolikephalites, which is now con-

sidered to be a microconch (Thierry 1978; Westermann

and Callomon 1988).

In Eucycloceratinae, adult micro- and macroconchs

look quite different; in many respects the microconchs

resemble the inner whorls of macroconchs as well as adults

of the K. lamellosus-D. subcompressus group. Eucycloceras

and K. lamellosus-D. subcompressus assemblages have a

slight stratigraphical overlap near the Lower and Middle

Callovian substage boundary. The holotype of ‘Eucycloceras

eucyclum’ and our one microconch specimen of Eucycloc-

eras come from the Golden Oolite of Keera, which is high-

est Lower Callovian. At Jumara we have been able to

collect one macroconch of Eucycloceras from the semilaevis

horizon, which is the same level. On the other hand, sev-

eral specimens of the K. lamellosus-D. subcompressus group

come from the basal Middle Callovian (Spath 1933,

p. 715, Table 4; pers. obs.). Thus the two groups form two


successive assemblages and are eudemic (cf. Callomon

1985), but the evolution involves cladogenesis. Eucycloceras

is large and its evolution appears to have been induced by

hypermorphosis. Evolutionary novelties, unlike the older

macrocephalitins, include an evolute shell, longer, coarse

primaries with adoral concavity, and disappearance of sec-

ondaries, which makes the adult periphery smooth in the

macroconch. Idiocycloceras, which soon rapidly evolved

from Eucycloceras, is still larger, more evolute and has

coarser ornamentation, and the evolution shows a para-

morphocline trend. Both genera coexisted, flourished in

great abundance for a short time, but suddenly became

extinct (or were ecologically excluded).

The beginning of the Middle Callovian saw rapid diver-

sification of many evolute forms belonging to Reineckeia,

Choffatia and Indosphinctes. Thus the Stephanocerataceae

of the Lower Callovian gave way to the Periphinctaceae in

both Europe and Kutch. All of these forms are large with

an evolute shell. Possibly the eucycloceratins in Kutch

faced stiff competition from the invading groups. Reine-

ckeiins, which flourished in the Early Callovian in Eur-

ope, suddenly invaded the Indo-Madagascan region

(Cariou and Krishna 1988) and in Kutch they are found

in strata below the Lower Callovian ⁄Middle Callovian

boundary. Choffatins, on the other hand, were present

during the Early Callovian in both areas, but diversified

AX B C

TEXT -F IG . 17 . A–C, Idiocycloceras perisphinctoides Spath [M], adult having more than half a whorl body-chamber with inner whorls

exposed, JUM 332, Bed 9, Jumara; · 0Æ25.

A B C

TEXT -F IG . 18 . A–C, Idiocycloceras perisphinctoides Spath [M], adult body-whorl fragment, JUM 489, Bed 9, Jumara; note dense

growth striae at aperture; · 0Æ25.


into many new species in the Middle Callovian in Kutch

(Spath 1928; pers. obs.). Furthermore, there was almost

certainly competition between Eucycloceras and the symp-

atrically derived Idiocycloceras. Sympatric groups generally

try to avoid competition by maintaining geographical seg-

regation or by ‘habitat proliferation’ within the same

region. We have already shown that both genera had the

same biogeographical distribution in Kutch and through-

out the Indo-Madagascan region (see also Basse and

Perrodon 1951; Donovan et al. 1981). However, in

the Subtethyan Himalaya, including Spiti and Tibet,

eucycloceratins have been reported from an assemblage

containing rare reineckeiins and choffatins (Pascoe 1959;

Krishnan 1982; Westermann and Wang 1988). These

might be areas where eucycloceratins migrated to avoid

competitive overlap. Pending studies of functional mor-

phology it is very difficult to know whether these two

genera exploited different ecological niches within the

same environment. However, indirect evidence suggests

that they competed for the same habitat. Eldredge (1974)

showed that while competing for the same ecological

niche two sympatric trilobite species displayed character

displacement. It appears that while Idiocycloceras

remained ‘neutral’, Eucycloceras (especially microconchs)

exhibited a ‘mixed reaction’. They diverged away and

even converged (e.g. E. opis var. obscura) with that of

Idiocycloceras (see ‘Discussion’ under Idiocycloceras peri-

sphinctoides). This perhaps explains the reason behind

the great infrasubspecific variation within the micro-

conchiate population of Eucycloceras. We do not seriously

consider the possibility of hybridization between them,

mainly on the grounds that the macroconchs are quite

distinct. Similarities in the nature of dimorphism between

two related sympatric taxa may complicate the situation

further. Similar size, the perisphinctid nature of coiling,

and bifurcating ribs persistent to the end may have

disrupted the ‘mate recognition’ system. Divergence of

Eucycloceras microconchs might have exaggerated the dif-

ferences in traits that distinguish them for mate recogni-

tion. It is interesting to note that microconchs of

reineckeiins and choffatins also closely resemble eucyclo-

ceratin microconchs with respect to the above features,

although they have lappets. One of the theoretical ecolog-

ical aspects of biological competition within a community

is that the size ratio for sympatric species is about 1:1Æ28(see Clarkson 1999, p. 49). Remarkably the two eucyclo-

ceratin species (including both dimorphs) correspond well

with this figure, as do all the major early Middle Callo-

vian species of Kutch. This suggests that eucycloceratins

successfully coexisted for some time, but were ultimately

excluded after a protracted struggle. Thus, it is possible

that because of the crisis from within, and stiff biological

competition from the reineckeiins and choffatins, the eu-

cycloceratins did not face extinction but were perhaps

ecologically excluded from the Indo-Madagascan region.

Two lines of evidence support this view. Firstly, the phys-

ical environment remained constant, an observation that

is based on the fact that similar lithofacies continue to

the top of anceps Zone (Datta 1992; Fursich et al. 1992),

and reineckeiins and choffatins remained equally diverse

and abundant. Secondly, a sudden faunal break in the eu-

cycloceratin lineage suggests ecological exclusion.

Where did they take refuge? Curently there is no evi-

dence that can shed light on this issue. It has already been

noted, however, that the Himalayan region, where both

macrocephalitin and eucycloceratin populations show

much homogeneity with that of the Kutch region, rarely

yields the perisphinctid group (especially reineckeiins),

which coexisted with eucycloceratins in the Indo-Madaga-

scan area. It is possible that, after being dramatically

excluded from the Indo-Madagascan area, the eucyclo-

ceratins thrived within a restricted geographical range in

the Himalayan region.

The Late Callovian history of Eucycloceratinae

remains unknown. The entire Himalayan region is

marked by a stratigraphical hiatus in which at least the

entire Upper Callovian is missing, although Kutch has a

near-continuous statigraphical record. The Mayaitinae

appeared everywhere during the Oxfordian, possibly rap-

idly, although the exact time is still debated. We suggest

that the Himalayan region is the centre of origin where

an isolated eucycloceratin population gave rise to May-

aitinae, since this area yields the highest diversity of

Mayaitinae, including Grayiceras. The Mayaitinae recall

the diversity of the older Macrocephalitinae of Indonesia

in that forms with radial and protracted sutures are

included. It is not surprising that the species with a

protracted suture, i.e. Paryphoceras badiense, is a homeo-

morph of E. opis var. opis [m], whereas the species with

a radial suture, i.e. Mayaites obesus, is a mayaitin equiv-

alent of Indocephalites diadematus. Soon the Mayaitinae

spread to the Kutch region, and like the Late Bathonian

migration of the Macrocephalitinae, not all of the forms

participated; Grayiceras remained Himalayan. Long-dis-

tance migration to the Pacific (South America) perhaps

resulted in the evolution of an entirely new subgenus,

Araucanites, within the Mayaitinae (Stipanicic et al.

1975).

Acknowledgements. A. Kayal (ONGC) and D. Mukherjee (GSI)

helped at various stages in the field. P. Rudra and P. Roy (JU)

assisted with computer analysis. S.S. Das (ISI) helped with pho-

tography. The Director, Curatorial Division, GSI, granted per-

mission for our study of the type material. Professor J. Hancock,

Dr N. Monks and an anonymous reviewer critically read the

manuscript and provided valuable suggestions. Two of us (SB

and KH) received financial aid from Department of Science and

Technology, India (ESS ⁄ 23 ⁄VES ⁄ 022 ⁄ 98).


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APPENDIX

1. Data matrix used to create the cladograms in Text-figure 8A–B

Character numbers refer to the list in Table 1.

Taxa

Characters

1 6 11 16 21

Otoitidae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Sphaeroceratinae 0 0 0 0 0 0 1 1 1 0 0 0 0 1 1 1 1 1 0 1 1 0 0 0 0

Eurycephalitinae 0 0 0 0 0 0 1 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 0 0 0

Macrocephalitinae 0 0 0 0 0 0 1 1 1 1 1 1 1 0 1 2 1 2 0 1 0 1 1 0 0

Eucycloceratinae 0 0 0 0 0 0 1 1 1 1 1 1 1 0 1 3 1 3 0 0 0 1 2 1 1

Mayaitinae 0 0 0 0 0 0 1 1 1 1 1 1 1 0 1 4 1 2 0 0 0 1 1 2 0


2. Data matrix used to create the cladogram in Text-figure 8C

Character numbers refer to the list given in Table 3.

Taxa

Characters

1 5 9 13 17 21 25

Macrocephalites 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nothocephalites 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 1 1 0 0 1 1 0 0 0 1 0 0

Eucycloceras 0 0 0 0 0 0 0 0 1 1 1 2 1 2 1 2 1 1 1 2 1 1 1 1 2 1 1

Idiocycloceras 0 0 0 0 0 0 0 0 2 0 1 2 1 2 1 2 1 0 1 2 0 0 2 1 2 2 2


EUCYCLOCERATIN AMMONITES FROM THE CALLOVIAN CHARI FORMATION, KUTCH, INDIA

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