Paterson, J.R. & Edgecombe, G.D., 2006. The Early Cambrian trilobite family Emuellidae Pocock, 1970:...

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J. Paleont., 80(3), 2006, pp. 496–513Copyright q 2006, The Paleontological Society0022-3360/06/0080-496$03.00

THE EARLY CAMBRIAN TRILOBITE FAMILY EMUELLIDAE POCOCK, 1970:SYSTEMATIC POSITION AND REVISION OF AUSTRALIAN SPECIES

JOHN R. PATERSON AND GREGORY D. EDGECOMBECentre for Ecostratigraphy and Palaeobiology, Department of Earth and Planetary Sciences, Macquarie University NSW 2109, Australia,

,[email protected]. and Australian Museum, 6 College Street, Sydney NSW 2010, Australia, ,[email protected].

ABSTRACT—The family Emuellidae Pocock, 1970 was established for Emuella Pocock, 1970 and Balcoracania Pocock, 1970 from theLower Cambrian of South Australia. Based on their peculiar trunk tagmosis, emuellids have been interpreted as the sister group of allother trilobites with dorsal facial sutures, and classified as high as the ordinal level. Cladistic analysis with a range of exemplar taxaof the Olenellina and Redlichiina instead resolves the emuellids within the Redlichiina, with tagmosis into a prothorax and opisthothorax(‘‘telosoma’’) nonhomologous in olenellines and emuellids. A taxonomic revision of Australian species identifies Balcoracania flindersias a junior subjective synonym of B. dailyi, whereas the two named species of Emuella are considered to be distinct. Balcoracaniadailyi possesses up to 103 thoracic segments, the maximum number recorded in any trilobite.

INTRODUCTION

THE EMUELLIDAE Pocock, 1970 are a group of East GondwananEarly Cambrian trilobites with an unusual combination of

morphological characteristics. Species of Emuellidae were firstdescribed by Pocock (1970) from Early Cambrian successions inSouth Australia, namely the Emu Bay Shale and White PointConglomerate on Kangaroo Island, and from the Billy Creek For-mation in the Flinders Ranges. Pocock erected two genera, eachwith two species, Emuella (E. polymera and E. dalgarnoi), andBalcoracania (B. dailyi and B. flindersi). Subsequently, Pocock(1974) documented a teratological specimen of Emuella poly-mera. Emuellids have also been documented from the LowerCambrian Shackleton Limestone of the Central TransantarcticMountains, Antarctica (Balcoracania? spp. of Palmer and Rowell,1995), and from the Lower Cambrian Yalkalpo-2 drillcore in theArrowie Basin, South Australia (Zang et al., 2001; Gravestock etal., 2001).

In the original treatment of the Emuellidae, Pocock (1970) clas-sified the family within the Redlichiina, making comparisons tosuch groups as Dolerolenidae and Protolenidae. He observedstrong similarities to the Olenellidae as well and, considering fa-cial sutures to be secondarily fused in olenellids, proposed ‘‘thatan ‘emuellid’ stock may have given rise to the olenellid branch’’(Pocock, 1970, p. 557). Pocock (1970, p. 559) advocated place-ment of the Emuellidae in the Redlichiina and suggested that ‘‘theEmuellidae appear to be very primitive, and must be placed nearthe origin of redlichiid evolution.’’ Zhang et al. (1980, fig. 73)provided a more explicit phylogenetic hypothesis for the emuel-lids, which they classified as a superfamily (Emuellacea) withinthe Redlichiina. They regarded trilobites with dorsal facial suturesto be a monophyletic group from which Olenellina were primi-tively excluded. Within the clade with dorsal sutures, Emuellaceawere depicted as sister group to all other members (Fig. 1.1).Other trilobite workers have differed in the placement of Emuel-lidae within the Redlichiina. Bergstrom (1973), for example, as-signed the Emuellidae to the superfamily Redlichiacea, a pheneticanalysis of Redlichiina by Lin (1990) clustered the Emuellidaewithin a revised concept of a superfamily Ellipsocephalacea, andthe Treatise classification of Redlichiina (Zhang et al., 1997) rec-ognizes a superfamily Emuelloidea separate from the Redlichioi-dea and Paradoxidoidea.

The Emuellidae figured prominently in a reappraisal of basaltrilobite relationships and chelicerate origins by Lauterbach (1980,1983, 1989). Lauterbach interpreted Trilobita in its traditionalsense as a paraphyletic group, within which Olenellinae are clos-est relatives of chelicerates, and trilobites with dorsal facial su-tures are the monophyletic sister group of Olenellinae and Chel-icerata. The clade with dorsal facial sutures formed the basis for

a redefined Trilobita, which according to Lauterbach (1980) isfundamentally split into Emuellida and Eutrilobita (Fig. 1.2).Three morphological characters were cited as evidence for thebasal position of Emuellida in relation to Eutrilobita. Firstly,emuellids have a long opisthothorax, interpreted by Lauterbachas a telosoma homologous with the opisthothorax (‘‘telosoma’’)of Olenellinae. Eutrilobita supposedly retain only a short remnantof this telosoma, the postpygidial abdomen of Cisne (1975, 1981),discussed below as nonexistent fide Whittington and Almond(1987). Secondly, emuellids supposedly lack a true pygidium,which Lauterbach regarded as an autapomorphy of Eutrilobita.The pygidium was thought to have originated as a cover for thereduced telosoma as part of a new enrollment mechanism in theEutrilobita. Thirdly, the narrow pleurae of the prothorax of emuel-lids were thought to be plesiomorphic relative to the broader pleu-rae in Eutrilobita. Lauterbach’s interpretation of Emuellida as sis-ter group to Eutrilobita in the context of trilobite paraphyly wasaccepted in textbooks (e.g., Ax, 1987) and reviews of arthropodphylogeny (e.g., Weygoldt, 1986).

Arguments for the inclusion of the Olenellina within the Tri-lobita, challenging the views of Lauterbach (1980, 1983), havebeen made by Fortey and Whittington (1989), Whittington (1989),Hahn (1989), and Ramskold and Edgecombe (1991), and do notwarrant further discussion here. Lauterbach’s (1980, 1983) viewsrelating to the systematic position of the emuellids within theTrilobita have received less scrutiny. Hahn’s (1989) defense oftrilobite monophyly involved classifying the emuellids as an orderEmuellida together with the Olenellida in the Protrilobita (Fig.1.3). Hahn (1989) accepted Lauterbach’s idea that Eutrilobita isa clade defined by a pygidium and the shortening of the trunk,such that the trilobite thorax was equivalent to the prothorax ofProtrilobita alone. Lauterbach (1989) rightly pointed out that theparaphyletic group Protrilobita does not merit recognition in aphylogenetic system.

The present study assesses the phylogenetic position of theEmuellidae within the Trilobita based upon a cladistic analysis ofrelevant Cambrian taxa. The study includes a taxonomic revisionof the South Australian species of Emuellidae, with a reexami-nation of the type collection originally described by Pocock(1970, 1974), and the description of new specimens from theWhite Point Conglomerate, Cape D’Estaing section, Kangaroo Is-land, and previously undocumented specimens from the CoadsHill Member of the Billy Creek Formation, Reaphook Hill, SouthAustralia.

CHARACTERS AND TAXONOMIC SAMPLING

We have aimed to test competing hypotheses of emuellid re-lationships (Fig. 1), in particular a sister-group relationship to allother Trilobita sensu Lauterbach (1980).

497PATERSON AND EDGECOMBE—EARLY CAMBRIAN TRILOBITE FAMILY EMUELLIDAE

FIGURE 1—Alternative hypotheses for the systematic position of emuel-lids. 1, Sister group of Eutrilobita sensu Lauterbach, with trilobitesmonophyletic (Zhang et al., 1980); 2, sister group of Eutrilobita (Lau-terbach, 1980, 1983, 1989), with trilobites paraphyletic; 3, sister groupof Olenellida (Hahn, 1989).

Sampling therefore considers a range of taxa that span the phy-logenetic scope of Olenellina and Redlichiina, and particularlyincludes groups that have previously been allied to emuellids.

Exemplar taxa that represent a variety of families were selected

based in part on quality and completeness of preservation. In asmany cases as possible, species were chosen for which articulatedspecimens are known so that thoracic characters could be scored.Availability of ontogenetic data was an additional considerationbecause characters from early ontogeny have been cited as im-portant in assessing basal trilobite relationships (e.g., Whittington,1989). Most species are of Early Cambrian age. Twenty-five spe-cies in addition to Emuella polymera and Balcoracania dailyiwere coded (see Table 1 for species and literature sources usedfor coding).

Characters bearing on higher-level relationships in publishedsources (e.g., Bergstrom, 1973; Fortey and Whittington, 1989;Whittington, 1989; Fortey, 1990; Briggs and Fortey, 1992; Geyer,1996; Jell, 2003) provided a starting point for the characters usedin the phylogenetic analysis. Relationships within the Olenellinasurveyed published datasets (Lieberman, 1998, 1999, 2001,2002).

Forty-five characters (see Table 2 for codings) were scored forthe 27 terminal taxa. They are as follows:

1. Dorsal ecdysial cephalic sutures: (0) absent; (1) present.Fortey and Whittington (1989) stated that the evidence for the

importance of the lack of dorsal ecdysial sutures in olenellines issomewhat equivocal. They mentioned that some workers (e.g.,Bergstrom, 1973; Lauterbach, 1980) argued that dorsal ecdysialsutures in olenellines were primitively absent, while others (e.g.,Bell, 1931; Hupe, 1953) regarded this absence to be secondary,resulting from fusion. Fortey and Whittington (1989) argued infavor of a primitive absence rather than a derived loss based ontwo lines of evidence: 1) sutures have not been observed in anintermediate olenelline population and 2) the phaselus growthstage lacks dorsal ecdysial sutures, hence during trilobite ontog-eny there is a change from lacking sutures to developing them.The assignment of the phaselus to trilobites is problematic (Chat-terton and Speyer, 1997), weakening this argument. An alternativehypothesis posits that dorsal ecdysial sutures evolved severaltimes (Repina, 1990; Geyer, 1996; Jell, 2003). Jell (2003) pro-posed that dorsal ecdysial sutures evolved independently from afallotaspidoid ancestor in at least five separate lineages.

2. Shape of glabellar margins: (0) tapering anteriorly or sub-parallel; (1) constricted between S1 and S3, with enlarged frontallobe; (2) expanding anteriorly.

State 1 codes for the glabellar constriction in the Olenelloidea.Emuellids also have the glabella constricted between S1 and S3,and likewise have an expanded frontal lobe. A more specific mod-ification of L3 in olenelloids is coded as character 11; the gla-bellar widening in Olenelloidea commences in front of S2 versusat S3 in emuellids.

3. Preglabellar field: (0) absent; (1) present.4. Plectrum on dorsal surface: (0) absent; (1) present.Fortey (1990) considered that the median plectrum in the preg-

labellar field is the dorsal expression of a backward ventral ex-tension from the rostral plate, therefore suggesting that redlichiinetaxa with a plectrum in the preglabellar field retained the conter-minant hypostomal condition. Jell (2003) challenged this idea byreevaluating the morphology of genera such as Eoredlichia Zhang(in Lu and Dong, 1952) and Bigotina Cobbold, 1935, suggestingthat several redlichiines that display a plectrum in the preglabellarfield have detached (natant) hypostomes. Based on these conflict-ing interpretations, this character and character 24 (hypostomalattachment) have been coded independently. Taxa coded as state0 for character 3 (lacking a preglabellar field) are coded as in-applicable for this character.

5. SO: (0) deepened laterally and shallow medially; (1) equaldepth across glabella.

State 0 is coded for taxa that display apodemal pits in the lateral

498 JOURNAL OF PALEONTOLOGY, V. 80, NO. 3, 2006

TABLE 1—Taxa included in the phylogenetic analysis and their associated references used for coding.

Taxa References

Olenellus fowleri Palmer, 1998 Palmer, 1957, pl. 19. figs. 1–3, 6, 11, 12, 16, 19Palmer and Halley, 1979, pl. 4, figs. 12, 15Palmer, 1998, fig. 10.1–10.6

Bristolia anteros Palmer and Halley, 1979 Palmer and Halley, 1979, pl. 1, figs. 1–13Nephrolenellus geniculatus Palmer, 1998 Palmer and Halley, 1979, pl. 4, figs. 7, 8

Palmer and Repina, 1993, fig. 4.3Palmer, 1998, fig. 6.1–6.9, 6.11–6.13

Wanneria walcottana (Wanner, 1901) Whittington, 1989, figs. 24, 28, 30, 32, 33, 35–38Levi-Setti, 1993, pl. 63Palmer and Repina, 1993, fig. 5Lieberman, 1999, fig. 11.1, 11.2

Elliptocephala asaphoides Emmons, 1844 Lochman, 1956, pl. 6, figs. 2–21Whittington, 1957, pl. 115, figs. 1–6Whittington, 1989, figs. 45, 46, 48, 50, 51Palmer and Repina, 1993, fig. 6.7Lieberman, 1999, fig. 12.1

Holmia kjerulfi (Linnarsson, 1871) Whittington, 1988, text-figs. 2, 3Whittington, 1990, figs. 13–19Palmer and Repina, 1993, fig. 6.1

Fallotaspis bondoni (Neltner and Poctey, 1950) Hupe, 1953, pl. 1, fig. 9; pl. 2, figs. 1–8; pl. 3, figs. 1, 3Geyer, 1996, figs. 8, 10.1–10.4, 20.1, 20.2, 23.1, 23.2, 25.1, 25.2, 26.1–26.4,

28, 31, 39.1–39.5, 39.7, 41a, 41b, 61.1–61.7, 62.1–62.8, 63.1–63.4Daguinaspis ambroggii Hupe and Abadie, 1950 Hupe, 1953, pl. 5, figs. 1, 4–12, 14

Geyer, 1996, figs. 13, 24.1, 24.2, 33, 35.2, 43.1–43.6, 67.1–67.8, 68.1–68.16Archaeaspis macropleuron Lieberman, 2002 Lieberman, 2002, figs. 3.2, 3.4, 3.8, 4.1, 4.2Repinaella sibirica (Repina in Khomentovskii and Repina, 1965) Khomentovskii and Repina, 1965, pl. 3, figs. 1–6

Geyer, 1996, fig. 69.1, 69.2Judomia tera Lazarenko in Kryskov et al., 1960 Demokidov and Lazarenko, 1964, pl. 7, figs. 6–9; pl. 8, figs. 1–8

Whittington, 1989, fig. 54aPalmer and Repina, 1993, fig. 10.7

Nevadia weeksi Walcott, 1910 Whittington, 1989, figs. 23, 39, 40, 41–44, 47, 49, 52, 53Fritz, 1992, pl. 1, figs. 1–11; pl. 2, figs. 1–6Palmer and Repina, 1993, fig. 10.1Fritz, 1995, fig. 9.6, 9.7Lieberman, 2001, fig. 3.1, 3.2

Emuella polymera Pocock, 1970 Pocock, 1970, pl. 106, figs. 1–7; pl. 107, figs. 1, 2; pl. 110, figs. 16–18Figure 3 (herein)

Balcoracania dailyi Pocock, 1970 Pocock, 1970, pl. 109, figs. 7, 8; pl. 110, figs. 1–15Figures 5–8 (herein)

Redlichia takooensis Lu, 1950 Zhang et al., 1980, pl. 23, figs. 1–14Bengtson et al., 1990, fig. 181

Eoredlichia intermediata Lu, 1940 Lu, 1940, pl. 1, figs. 1–10Zhang, 1962, pl. 1, fig. 1a–bZhang et al., 1980, pl. 33, figs. 9–14; pl. 34, figs. 1–6; pl. 36, figs. 3, 4Shu et al., 1995, figs. 4, 5, 7, 11, 15; pl. 1, figs. 1–8

Lemdadella antarcticae Palmer in Palmer and Rowell, 1995 Palmer and Rowell, 1995, fig. 8.1–8.17Dolerolenus zoppii (Meneghini, 1882) Nicosia and Rasetti, 1970, pl. 1, figs. 1–11; pl. 2, figs. 1–3

Rasetti, 1972, pl. 15, figs. 1–14; pl. 16, figs. 1–6Whittington, 1988, text-fig. 7Levi-Setti, 1993, pls. 66, 67

Yinites wanshougongensis Zhang and Lin in Zhang et al., 1980 Zhang et al., 1980, pl. 60, figs. 7–9; pl. 61, figs. 1–14; pl. 62, fig. 1Abadiella huoi (Zhang, 1966) Bengtson et al., 1990, figs. 183a–g, j, k, 184Eccaparadoxides pusillus (Barrande, 1846) Snajdr, 1958, pl. 20, figs. 1–46; pl. 21, figs. 1–19; pl. 22, figs. 1–15

Levi-Setti, 1993, pl. 90Anabaraspis splendens Lermontova, 1951 Lermontova, 1951, pl. 13, fig. 1a–g

Demokidov and Lazarenko, 1964, pl. 22, figs. 1–8; pl. 23, figs. 1–6Savitsky et al., 1972, pl. 13, figs. 6, 7

Xystridura templetonensis (Chapman, 1929) Opik, 1975a, pl. 13, fig. 5; pl. 15, figs. 3, 5; pl. 20, figs. 3–10; pl. 21, figs. 1–6;pl. 22, figs. 1–5

McNamara, 1981, figs. 6b, 6c, 7c, 7dBigotina bivallata Cobbold, 1935 Pillola, 1993, pl. 2, figs. 1–6; pl. 3, figs. 1–9; pl. 4, figs. 1–7; pl. 5, figs. 1–3,

5–7, 10; pl. 6, figs. 1–8; pl. 7, figs. 1–9Estaingia bilobata Pocock, 1964 Pocock, 1964, pl. 75, figs. 1–6; pl. 76, figs. 1–6

Bengtson et al., 1990, fig. 199a–iNedin, 1995, fig. 5

Ichangia ichangensis Zhang, 1957 Zhang et al., 1980, pl. 76, figs. 4–8Zhang and Pratt, 1999, figs. 5.1–5.16, 6.11–6.15, 7.11–7.16

Ellipsocephalus gripi (Kautsky, 1945) Kautsky, 1945, pl. 11, fig. 1; pl. 13, figs. 8–12; pl. 14, figs. 6–8; pl. 15, figs. 1–8; pl. 16, figs. 1–14; pl. 17, figs. 4–8; pl. 18, figs. 1–9

Ahlberg and Bergstrom, 1978, pl. 1, figs. 6–10


TABLE 2—Species and character codings used in the phylogenetic analysis(references used for coding are presented in Table 1). Polymorphic char-acters are indicated by ‘A’ (states 0 1 1) and ‘B’ (states 1 1 2).

Olenellus fowleri011100003- 1100000000 111?000001 100-020-01 11010Bristolia anteros010-000001 1101000101 011????0?? ????????01 1101?Nephrolenellus geniculatus010-000001 112-000110 011?000000 10??????01 1101?Wanneria walcottana010-000000 1112000100 00??100000 0-10020-?? ?????Elliptocephala asaphoides0110000011 1112000000 001?100000 0-10?01001 11011Holmia kjerulfi010-000011 1112000000 1110100010 0-10000-?? ?????Fallotaspis bondoni0010100000 0102100000 001?100110 101000???1 1?0??Daguinaspis ambroggii0010100000 0100100010 001?100110 0-0-000-01 1001?Archaeaspis macropleuron0011100000 0100100000 011??00000 10???????? ?????Repinaella sibirica0010100000 00––100000 001???001? ?????????? ?????Judomia tera010-100011 0112000000 000?100000 0-11020-?? ?????Nevadia weeksi0011000000 0100000100 001?000001 0-11000-?? ?????Emuella polymera110-110101 0202110121 0100011110 1111000-11 0010?Balcoracania dailyi1111110101 0202110120 0100011110 11??000-11 00100Redlichia takooensis1011111121 0???100001 0100100010 0-10111011 1000-Eoredlichia intermediata1011111000 00––100101 0100100010 0-11101011 1000-Lemdadella antarcticae1011111000 0102100110 000??????? ??11000-11 1010?Dolerolenus zoppii1011100001 010?000100 0001100000 0-100010?? ?????Yinites wanshougongensis100-111000 00––00010? 010?10?010 0-11001111 10001Abadiella huoi1011000000 0102100121 010?101010 0-110010?? ?????Eccaparadoxides pusillus120-111101 010B000020 0000100000 0-11010-10 10011Anabaraspis splendens12101AA001 0112000020 0000100000 0-11010-?? ?????Xystridura templetonensis120-1AA001 011B000020 0000100000 0-11011110 10011Bigotina bivallata1011100000 0101100120 010??0??1? ??11000-?0 1000?Estaingia bilobata1011100000 0102000120 010?101010 0-11101110 10101Ichangia ichangensis1211100000 010200112? 0?0??????? ??11001110 1011?Ellipsocephalus gripi101010000A 010200112? 010?101010 0-11001010 1011?

portions of SO, e.g., Abadiella huoi (Jell in Bengtson et al., 1990,fig. 183a, c, j).

6. S1: (0) confined laterally; (1) transglabellar.Some taxa that have been coded as state 0 show a shallow

connection medially, e.g., Fallotaspis bondoni (Hupe, 1953, pl.2; Geyer, 1996, figs. 39, 62) and Bigotina bivallata (Pillola, 1993,pl. 3, fig. 1a; pl. 4, fig. 2; pl. 5, fig. 3).

7. Shape of S1: (0) straight or weakly convex; (1) stronglyconvex posteriorly.

8. S2: (0) confined laterally; (1) transglabellar.Some taxa that have been coded as state 0 show a shallow

connection medially, e.g., Fallotaspis bondoni (Hupe, 1953, pl.2; Geyer, 1996, figs. 39, 62).

9. Shape of S2: (0) straight or weakly convex; (1) stronglyconvex anteriorly; (2) strongly convex posteriorly; (3) isolatedpits.

10. Orientation of S2: (0) directed forwards abaxially; (1) trans-verse.

11. L3 flexed backwards abaxially at the expense of L2: (0)abaxial part of L3 unmodified; (1) abaxial part of L3 flexed back-wards.

A modified L3 (Palmer and Repina, 1993) has been cited assynapomorphic for Olenelloidea and is shared by the olenelloidexemplars coded herein. Other taxa do not have a correspondingmodification of the posterolateral part of L3.

12. S3: (0) absent; (1) confined laterally; (2) transglabellar.13. Shape of S3: (0) straight or weakly convex; (1) strongly

convex anteriorly; (2) isolated pits.14. Orientation of S3: (0) directed forwards abaxially; (1) di-

rected backwards abaxially; (2) transverse.15. Parafrontal band: (0) absent; (1) present.Definition of the parafrontal band follows Pillola (1993). This

character is similar to character 7 of Lieberman (2002) in whichonly taxa that show a visible parafrontal band have been codedas state 1.

16. Fossulae: (0) absent; (1) present as small, discrete pits.Emuellids have a small, clearly incised fossular pit at the junc-

tion between the palpebro-ocular ridge and frontal lobe of theglabella (Fig. 6.8–6.10) that is not similarly developed in anyother terminal taxa in this analysis.

17. Palpebral lobe and ocular ridge: (0) continuous, undiffer-entiated; (1) distinctly differentiated with impression of a shallowfurrow isolating palpebral lobe.

18. Posterior tips of palpebro-ocular ridge developed opposite:(0) LO or SO; (1) L1 or S1.

19. Width (tr.) of interocular area adjacent to posterior tip ofpalpebro-ocular ridge: (0) less than one-third the width (tr.) of theoccipital ring; (1) one-third to half the width (tr.) of the occipitalring; (2) more than half the width (tr.) of the occipital ring.

20. Genal angle developed opposite: (0) LO or posterior of LO;(1) L1 or anterior of L1.

21. Intergenal spine: (0) absent; (1) present.22. Intergenal angle: (0) absent; (1) present.23. Intergenal ridge: (0) absent; (1) present.24. Hypostomal attachment: (0) conterminant; (1) natant.Hypostomal attachment in relation to trilobite phylogeny has

been discussed in much detail by Fortey (1990), whose conclu-sions were challenged by Jell (2003). As discussed above, thischaracter is considered independent of character 4 and has onlybeen coded for those taxa whose ventral cephalic morphology canbe observed. The holotype of Balcoracania flindersi (5B. dailyi)has preserved the ventral expression of the hypostome in situ(Pocock, 1970, pl. 109, fig. 7; Fig. 8.3), and has been coded asstate 0. A natant hypostome is present in only a single terminalin our sample, rendering the character cladistically uninformative,but we include it because of the significance that it has beenattributed in recent studies.

25. Tagmosis of thorax: (0) pro- and opisthothorax differenti-ated; (1) pro- and opisthothorax undifferentiated.

26. Thoracic segments 5 and 6: (0) free; (1) fused.The fusion of the fifth thoracic segment to the macropleural

sixth segment was cited by Pocock (1970) in the diagnosis ofEmuellidae and was interpreted by Lauterbach (1980) as an au-tapomorphy of Emuellida.

27. Thoracic articulation: (0) nonfulcrate; (1) fulcrate.As noted by Whittington (1997, p. 50–51), the fulcrate condi-

tion, i.e., the presence of a fulcrum in the thoracic pleurae, iscommon among most trilobite groups. Opik (1970, p. 3–5) rec-ognized that Redlichia Cossmann, 1902 and olenellines lack thefulcrum (i.e., nonfulcrate). Several other studies (Bergstrom,1973; Bergstrom and Levi-Setti, 1978; Whittington, 1989, 1990)have also discussed the nonfulcrate condition in olenellines and


paradoxidids. Opik (1970) suggested the possibility of using thischaracter in higher-level classification, although he later noted thatsome groups display both conditions (Opik, 1975a, p. 23). Forexample, Opik (1975a) demonstrated that xystridurid genera candisplay both conditions, with the fulcrum being absent in Xystri-dura Whitehouse, 1936 and present in Galahetes Opik, 1975a.

28. Width (tr.) of thoracic axial ring on T1: (0) 20%–40% width(tr.) of thoracic segment; (1) 45%–65% width (tr.) of thoracicsegment.

This character measures the relative width of the pleurae onthe anterior part of the prothorax, narrow pleurae (state 1) alleg-edly being plesiomorphic in emuellids fide Lauterbach (1980).

29. Thoracic pleural spines: (0) falcate; (1) nonfalcate (‘‘thorn-like’’).

The terminology for this character follows the morphologicalnomenclature for the thoracic pleural spines used by Palmer andRepina (1993, fig. 2).

30. Length of pleural spines along thorax: (0) of equal lengthor slightly increasing or decreasing posteriorly; (1) strongly in-creasing posteriorly.

Taxa with a pro- and opisthothorax have been coded in relationto the length of the pleural spines on the prothorax. Judomia teraLazarenko (in Kryskov et al., 1960) is coded based on the gradualincrease in length of the pleural spines in typical material (De-mokidov and Lazarenko, 1964, pl. 7, fig. 8; Palmer and Repina,1993, fig. 10.7) but a specimen assigned to that species by Sav-itsky et al. (1972, pl. 8, fig. 2) shows a greater increase in lengthposteriorly. Lieberman (1998) considered the longer-spined spec-imen to represent a different species.

31. Macropleural thoracic segment: (0) absent; (1) present.This character was employed by Lauterbach (1980), and sub-

sequently discussed by Fortey and Whittington (1989) and Ram-skold and Edgecombe (1991). Presence of a macropleural seg-ment is coded independently of its segmental position (character32).

32. Position of macropleural thoracic segment: (0) developedon third segment; (1) developed on sixth segment.

33. Pygidial axis: (0) unsegmented; (1) segmented.34. Number of pygidial axial rings: (0) one; (1) two or more.This character has been discussed by Fortey and Whittington

(1989, p. 128–129; their character 4) and Ramskold and Edge-combe (1991, p. 271–272). Taxa having an unsegmented axis(character 33, state 0) are coded as inapplicable for this character.

35. Bilobate pygidial terminal piece: (0) absent; (1) present.A pair of rounded swellings in the terminal part of the pygidial

axis is most pronounced in Metaredlichiinae (Zhang et al., 1980,fig. 57), but can be discerned in Redlichiinae (Redlichia) and Par-aredlichiinae (Eoredlichia). A pair of terminal swellings is alsopresent in Estaingia Pocock, 1964 (pl. 76, figs. 3, 6).

36. Posteromedial margin of pygidium: (0) smooth; (1) withshallow, rounded concavity; (2) with deep, acutely V-shapednotch.

Taxa that possess a deep, V-shaped notch [e.g., Olenellus fow-leri Palmer, 1998, Wanneria walcottana (Wanner, 1901), Judomiatera] give the impression of a pair of backwardly directed borderspines. However, it is unlikely that this feature is homologouswith pygidial pleural spines that represent lateral extensions ofthe pygidial pleurae.

37. Pygidial spines: (0) absent; (1) present.38. Pygidial spine morphology: (0) single pair of short, lateral

spines; (1) two or more pairs of spines.39. Calcified protaspid stage: (0) absent; (1) present.See Fortey and Whittington (1989, p. 135), Ramskold and Ed-

gecombe (1991, p. 277), and Chatterton and Speyer (1997, p. 219)for a detailed discussion of this character. A protaspis has beenassigned to Fallotaspis Hupe, 1953 (Geyer, 1996, fig. 41) but the

quality of preservation is too poor to be confident that the spec-imen is not an early meraspid.

40. Transverse furrows on interocular cheeks in protaspid andearly meraspid stages: (0) absent; (1) present.

Fortey and Whittington (1989, p. 133) suggested that expressedsegmentation of the interocular cheeks in olenelloids is primitive,since it is ‘‘not so expressed’’ in the ontogenies of redlichioidsand ‘‘higher’’ trilobites. However, such segmentation is clearlyevident in a variety of redlichioid taxa, such as the emuellids(Pocock, 1970, pl. 110, figs. 2, 4, 5, 10), Redlichia takooensis Lu,1950 (Zhang et al., 1980, pl. 23, fig. 3), and Lemdadella antarc-ticae Palmer (in Palmer and Rowell, 1995, fig. 8.1).

41. Anterior cranidial/cephalic border in protaspid and earlymeraspid stages: (0) absent; (1) present.

Chatterton and Speyer (1997, p. 219) considered the absenceof an anterior border in juvenile emuellids to be significant amongEarly Cambrian trilobites.

42. Procranidial spines in early meraspid stage: (0) absent; (1)present.

Whittington (1989, p. 140) argued that procranidial spines areunique to olenelloids.

43. Expanded frontal lobe in early meraspid stage: (0) absent;(1) present.

44. Intergenal/fixigenal spine in early meraspid stage: (0) ab-sent; (1) present.

45. Macropleurality during ontogeny: (0) macropleural segmentpresent in meraspid stages and retained in late holaspides; (1)macropleural segment/s present in meraspid stages but absent inlate holaspides.

Nedin and Jenkins (1999) noted the presence of elongate tho-racic pleural spines on the first two segments in early meraspidesof Estaingia, Xystridura, and paradoxidoids, and their subsequent‘loss’ in later ontogeny. This condition also occurs in Yinites wan-shougongensis Zhang and Lin (in Zhang et al., 1980, pl. 61, fig.4). Early meraspides of Elliptocephala asaphoides Emmons, 1844possess macropleural spines on the third thoracic segment (Whit-tington, 1957, pl. 115, figs. 2, 4) that are subsequently lost inholaspides. These conditions have been coded as state 1.

CLADISTIC ANALYSIS

Cladograms were rooted between Olenellina and the remainingtaxa (emuellids and Eutrilobita). In order to test the possibilitythat trilobites with dorsal facial sutures could be polyphyletic,with multiple separate origins from within the Olenellina (Jell,2003), monophyly of the ingroup was not constrained. Multistatecharacters were analyzed as unordered.

A heuristic search with PAUP*4.0b10 (Swofford, 2002) used1,000 random stepwise addition sequences, saving five trees perreplicate, then subjecting those trees to TBR (Tree Bisection-Re-connection) branch swapping to completion. Node support wasevaluated by parsimony jackknifing with PAUP*. One thousandjackknife replicates each employed the same heuristic search pro-tocol as described above, using JAC resampling with 37% char-acter deletion.

RESULTS AND DISCUSSION

Analysis with the parameters described above resulted in 24shortest cladograms of 127 steps (Consistency Index 0.417, Re-tention Index 0.670, Rescaled Consistency Index 0.280). Figure2 is the strict consensus of these cladograms, showing those nodesthat are supported in 50% or more of the jackknife replicates.

Monophyly of the Emuellidae (Emuella 1 Balcoracania) issupported by a glabellar constriction behind an expanded frontallobe (ch. 2), transverse, transglabellar S2 (chs. 8, 10), transgla-bellar S3 (ch. 12), fossulae (ch. 16), prothoracic/opisthothoracictagmosis (ch. 25), fused fifth and sixth thoracic segments (ch. 26),


FIGURE 2—Strict consensus of 24 shortest cladograms for character datain Table 2. Numbers at nodes are jackknife frequencies greater than50%.

wide thoracic axial rings (ch. 28), macropleurae on thoracic seg-ment 6 (chs. 31, 32), and a lack of an anterior cranidial borderin early ontogeny (ch. 41). Under ACCTRAN (accelerated trans-formation) optimization, the presence of the macropleural seg-ment in meraspides and its retention in holaspides (ch. 45) isautapomorphic for Emuellidae.

The emuellid clade is nested within the Redlichiina rather thanexcluded from it. Emuellids are thus members of the Eutrilobitaas defined by Lauterbach (1980, 1983) rather than being the sistergroup of Eutrilobita (contra Fig. 1.2). The cladogram in Figure 2conforms to the phenogram and classification of Lin (1990) inthat the Emuellidae are resolved in a clade with members of theEllipsocephaloidea as redefined by Lin (1990). The clade in Fig-ure 2 that includes Emuellidae, Bigotina, Abadiella Hupe, 1953,Estaingia, Ichangia Zhang, 1957 and Ellipsocephalus Zenker,1833 corresponds to Ellipsocephaloidea as defined by Lin (1990)except for the inclusion of Abadiella. The genera ParabadiellaZhang, 1966 [5Abadiella fide Jell (in Bengtson et al., 1990) andJago et al. (2002), contra Zhang et al. (2001)] and Bigotina have,however, been discussed as intermediates between Redlichioideaand Ellipsocephaloidea (Zhang, 1987, 1992), a view that broadlyconforms to the placement of these genera in Figure 2.

Regarding the higher-level relationships within the Redlichiina,

Redlichioidea (in the sense of Zhang et al., 1980, 1997; Lin, 1990)is resolved as paraphyletic with respect to Ellipsocephaloidea andParadoxidoidea. Xystriduridae and Paradoxididae are depicted asclosely related, as had been argued by Opik (1975a), Whittington(1988), and Lin (1990), rather than attributing their similarities toconvergence as favored by Jell (in Bengtson et al., 1990). Thecladogram depicts a relatively basal position for Dolerolenidae inthe Redlichioidea, in broad agreement with a phylogenetic treeby Zhang et al. (1980, fig. 72). Ichangiidae and Estaingiidae areresolved as related to Ellipsocephaloidea (Jell in Bengtson et al.,1990). However, the cladogram disagrees with Opik (1975a,1975b), Jell (in Bengtson et al. 1990), and Nedin and Jenkins(1999) regarding an alleged close relationship of Estaingia to theXystriduridae. Results support Opik’s (1968) suggestion that Bi-gotina is related to ellipsocephalids and protolenids, and his sub-sequent placement of the Bigotininae in the Ellipsocephaloidea(Opik, 1975b). None of the nodes that nest the emuellids withinthe Redlichiina are present in more than half of the jackknifereplicates. The node that unites emuellids with Redlichiina to theexclusion of Dolerolenus Leanza, 1949, Xystridura, and the par-adoxidids has several characters that optimize as synapomorphies[10(0), 15(1), 29(1), 43(1), 44(0)], but all have consistency indi-ces of 0.5 or less.

Relationships depicted within the Olenellina (Fig. 2), such asthe grouping of Fallotaspidoidea, are weakly supported. The Ole-nellina were undersampled in terms of the characters bearing ontheir internal phylogeny, here serving principally as outgroups.We refer the reader to more exhaustive character/taxonomic sam-pling by Lieberman (1998, 2001, 2002).

The following discussion considers morphological charactersthat have figured prominently in basal trilobite phylogeny.

Dorsal facial sutures.A single origin of dorsal facial suturesis more parsimonious than multiple origins, and this charactermaps onto all shortest cladograms once (as in Lieberman, 2002).Adherents of the multiple origins hypothesis (e.g., Repina, 1990;Geyer, 1996; Jell, 2003) have drawn on similarities between par-ticular fallotaspidoids and redlichiines in specific sections in Mo-rocco and Siberia, but no one has as yet documented transitionalstages in the manyfold origins of these sutures. Morphologicalcharacters cited by Jell (2003) in defense of eutrilobite polyphylyhave been included in our analysis (e.g., glabellar shape, ch. 2;preglabellar field, ch. 3; presence of a plectrum, ch. 4; width ofthe interocular area, ch. 19) and found to be more homoplasticthan are dorsal ecdysial sutures. We do not find this result to besurprising, given the complexity and uniqueness of the trilobiteecdysial suture system in the context of ecdysial sutures acrossthe Arthropoda. Ax (1987, p. 213) was justified in stating that‘‘the facial sutures and the remarkable method of moulting areseen as apomorphies evolved only once.’’

Tagmosis.Mapped onto each of the shortest cladograms, tag-mosis into a prothorax and opisthothorax has multiple origins inthe Trilobita. It originates at least twice in the cladograms in Fig-ure 2 (either independently or once in Nevadia Walcott, 1910 andolenelloids, with an independent gain in emuellids). Olenellinawith a differentiated opisthothorax have prothoracic/opisthothor-acic tagmosis decoupled from the position of the macropleuralsegment whereas in emuellids the opisthothorax commences im-mediately behind the macropleural segment. Under the hypothesisthat the opisthothorax in Emuellidae and in Olenellina is nonho-mologous, this morphology (telosoma fide Lauterbach, 1980) can-not be reconstructed at the basal nodes of Trilobita or Arachnata.Macropleural thoracic segments have multiple independent gainsin the Olenellina and each occurrence is convergent with the ma-cropleural segment in Emuellidae.


Lauterbach’s (1980) hypothesis that the opisthothorax is re-tained in Eutrilobita as a short postpygidial abdomen drew en-tirely upon Cisne’s (1975, 1981) interpretation of Triarthrus ea-toni (Hall, 1838), which supposedly had such a tagma projectingfrom behind the pygidium. The specimens upon which Cisnedrew his data in support of the postpygidial abdomen were re-evaluated by Whittington and Almond (1987), and the allegedpostpygidial abdomen was revealed to be series of pygidial ap-pendages. No evidence supports the existence of a telosoma orpostpygidial abdomen in Eutrilobita.

Fulcrate thorax.Fulcrate thoracic articulation (ch. 27) fits allshortest cladograms with 100% consistency, mapping on as a syn-apomorphy for a group that unites emuellids with Bigotina, Aba-diella, Estaingia, Ichangia, and Ellipsocephalus. This supports anearlier view of Whittington (1989, p. 141) regarding the inclusionof the ellipsocephaloids within the Redlichiida. He suggested thatinclusion of the ellipsocephaloids would rest upon the similaritiesin glabellar and palpebro-ocular ridge morphology, but furthermentioned that ‘‘inclusion of them adds a group in which theinner portion of the pleura hinges along the straight, horizontaledge, the outer portion bent down at the fulcrum and facetted.’’

Pygidium.A true pygidium was identified by Lauterbach(1980, 1983) and Hahn (1989) as an autapomorphic character ofEutrilobita, thought to be lacking in Olenellina and Emuellida.This view is contradicted by multisegmented pygidia in variousolenellids (e.g., Fritz, 1972, pl. 7, figs. 14–17; Ahlberg et al.,1986, fig. 13). Likewise we dispute the view that emuellids lacka pygidium, and confirm Pocock’s (1970) description of a mul-tisegmented pygidium in Emuella dalgarnoi. In the best-preservedspecimen of that species (Fig. 4.3), the pygidium is differentiatedfrom the opisthothorax by its smooth margin, the axial furrowsbecome indistinct, and four axial rings can be discerned. Only theanteriormost pleural rib is defined by furrows. Whittington (1989)likewise considered that a pygidium including the telson and ad-ditional segments was present in Olenellina and Emuellidae, as inthe Eutrilobita.

Transverse furrows on interocular cheeks in protaspides andearly meraspides.Fortey and Whittington (1989) and Whitting-ton (1989) identified transverse furrows that delimit segmentationon the interocular cheeks (ch. 40) as a general character for Tri-lobita including Olenellina. Suppression of these furrows occurredtwice on the cladogram in Figure 2, once in a clade that unitesxystridurids with paradoxidids, and separately in a clade that in-cludes Bigotina, Estaingia, Ichangia, and Ellipsocephalus but ex-cludes the Emuellidae, which primitively retain these furrows (Po-cock, 1970, pl. 110, figs. 2, 4, 5, 10; Fig. 8.5).

SYSTEMATIC PALEONTOLOGY

Studied material includes Pocock’s (1970) type collection(AUGD16643–16706) housed at the South Australian Museum,Adelaide. Additional specimens from the White Point Conglom-erate, Cape D’Estaing section, Kangaroo Island (Pocock, 1970,text-fig. 2), are housed in the paleontological collections of theSouth Australian Museum (SAMP35510–35525, 40265–40276)and the Australian Museum, Sydney (AMF98278–98371, all Bal-coracania dailyi). Previously undescribed and unillustrated ma-terial of Balcoracania dailyi from the Coads Hill Member of theBilly Creek Formation, Reaphook Hill, South Australia (seeMoore, 1980 for locality information), is housed at the SouthAustralian Museum (SAMP14543–14571). Specimens of Emuellapolymera from the private collection of Dave Simpson (Adelaide,South Australia), collected from the type locality, were also ex-amined and photographed. The terminology employed followsWhittington and Kelly (1997).

Family EMUELLIDAE Pocock, 1970Discussion.The monotypic genus Holyoakia Palmer in Palm-

er and Rowell, 1995, from the Shackleton Limestone, CentralTransantarctic Mountains, was placed ‘‘with serious reservationin the Emuellidae to focus attention on the numerous cranidialsimilarities’’ (Palmer and Rowell, 1995, p. 15). We disagree withthis assignment on the basis of pygidial morphology. The pygidiaof Emuella and Balcoracania are minute, have very poorly de-veloped axial furrows and weakly developed segmentation in theaxis and pleural fields, and possess a smooth margin. The pygid-ium of Holyoakia is of subequal size with the cranidium, has awell-defined axis with eight axial rings and a terminal piece, well-developed pleural ribs and furrows, and a spinose margin. Wesuggest that Holyoakia would be better placed within the Dory-pygidae based on the above-mentioned pygidial characteristicsand the following cranidial characteristics: subquadrate glabella,absence of a preglabellar field, short (exsag.) preocular field, well-differentiated eye ridge and palpebral lobe, and wide (tr.) pos-terolateral projection.

Genus EMUELLA Pocock, 1970Type species.Emuella polymera Pocock, 1970, Early Cam-

brian, White Point Conglomerate, Kangaroo Island, South Aus-tralia; by original designation.

Revised diagnosis.Cephalon subpentagonal in outline; width(tr.) of posterior margin abaxial to intergenal angle 80%–150%its width adaxial to intergenal angle; anterior sections of facialsuture diverging anteriorly at 158–508 between g and b; pregla-bellar field absent; palpebral lobe length (exsag.) 17%–27% cran-idial length, anterior tip of lobe situated opposite L3, posterior tipof lobe situated opposite S1; thorax with an observed maximumof 58 segments (52 opisthothoracic segments); width (tr.) of pro-thoracic axis 50%–60% width of prothoracic segment.

Discussion.Emuella and Balcoracania can be easily differ-entiated by the outline of the cephalon, width (tr.) of the posteriormargin relative to the intergenal angle, angle of divergence of theanterior sections of the facial suture, presence or absence of apreglabellar field, length (exsag.) and position of the palpebrallobe, and the width (tr.) of the prothoracic axis. Pocock (1970,text-fig. 6) demonstrated statistically that Emuella can be distin-guished from Balcoracania based on the length of the palpebrallobe relative to cranidial length, despite some minor overlap. Al-though Pocock’s (1970) generic diagnoses include some of thegeneric characters used herein, others incorporated by him appearto be unreliable. For example, Pocock (1970, p. 528) suggestedthat the anterior border furrow in Emuella ‘‘shallows abruptlyanterior to frontal glabellar lobe,’’ but some specimens of Emuellapolymera and E. dalgarnoi display a continuous anterior borderfurrow (Figs. 3.1, 3.7, 4.1, 4.7). The medial ‘‘shallowing’’ of theanterior border furrow referred to by Pocock is the result of theparafrontal band merging with the anterior cranidial border insome specimens (Figs. 3.8, 3.11, 4.4, 4.6). Pocock (1970) alsodifferentiated Emuella and Balcoracania based on the terminationof the thoracic pleural furrows relative to the pleural spine, butthere appears to be no difference in the position of the distal tipof the pleural furrows between Emuella and Balcoracania.

EMUELLA POLYMERA Pocock, 1970Figure 3

Emuella polymera POCOCK, 1970, p. 528, pl. 106, figs. 1–7; pl. 107, figs.1, 2; pl. 110, figs. 16–18; 1974, figs. 1, 2.

Revised diagnosis.Width of posterior cranidial margin ab-axial to intergenal angle 130%–150% its width adaxial to inter-genal angle; sutural ridge on posterior section of facial sutureabsent; anterior sections of facial suture diverging anteriorly at


158–308 between g and b; palpebral lobe length (exsag.) 17%–23% cranidial length (sag.); eye ridges diverging posteriorly at1358–1458; posterior cranidial border furrow evenly deep (tr.).

Description.Cephalon moderately small, sagittal length up to8.1 mm; subpentagonal in outline; low convexity (sag., tr.). Cran-idium subquadrate in outline; sagittal length approximately 70%–80% width (tr.) of posterior margin; anterior margin gently tomoderately curved; posterior margin (excluding occipital ring)straight to intergenal angle (1358–1408), then strongly directedanterolaterally, width (tr.) of posterior margin abaxial to intergenalangle 1308–1508 its width adaxial to intergenal angle. Anteriorsections of facial suture diverging anteriorly at 158–308 betweeng and b, then strongly converging between b and a. Posteriorsections of facial suture short, diverging posteriorly at 908 be-tween « and v; sutural ridge absent. Glabella strongly taperinganteriorly from posterior margin to S1, gently tapering betweenS1 and S3, then expanding into frontal lobe; frontal lobe broadlyrounded with anterior margin reaching anterior border furrow,width (tr.) 67%–77% width of LO; moderate convexity (tr.); sag-ittal length (including LO) 85% cranidial length. Axial furrowshallow and of moderate width (tr.); fossula at junction of pos-terolateral corner of frontal lobe and anterior margin of eye ridgevariably developed, ranging from obscure to small, discrete pit.S1 weakly to moderately impressed, transglabellar, abaxial por-tions directed slightly posteromedially, becoming transverse sag-ittally; S2 and S3 weakly to moderately impressed, transglabellar,transverse. Occipital ring moderately convex (tr.), length (sag.)16%–20% cranidial length; anterior margin weakly convex pos-teriorly; posterior margin bowed posteriorly. SO straight to weak-ly convex posteriorly, moderately wide (sag., exsag.), deep acrossits entire width. Preglabellar field absent. Preocular fixigenal fieldgently downsloping anteriorly, gently convex, length (exsag.)15%–20% cranidial length (sag.). Anterior border weakly to mod-erately convex, length (sag.) 12%–14% cranidial length, borderlength (exsag.) strongly tapers abaxially; anterior border furrownarrow (sag., exsag.). Palpebral lobe well developed, stronglyconvex, length (exsag.) 17%–23% cranidial length (sag.), widthapproximately 35%–50% lobe length, anterior tip situated oppo-site L3, posterior tip situated opposite S1; palpebral furrow shal-low, moderately wide (tr.). Eye ridge well developed, forming acontinuation of the palpebral lobe, flat to weakly convex (exsag.),straight to weakly convex anteriorly, ridges diverge posteriorly at1358–1458; eye ridge divided into inner and outer bands by weak-ly developed ocular furrow, inner and outer bands merge withposterolateral portion of frontal glabellar lobe; parafrontal bandweakly developed. Palpebral area moderately convex, width at «(tr.) 70%–85% adjacent glabellar width. Postocular area of ap-proximately equal length (exsag.) of palpebral area. Posterolateralprojection of fixigena very short (tr.), strongly tapers abaxially.Posterior border moderately convex (exsag.), moderately expand-ing abaxially to intergenal angle, then tapering to distal end ofborder; posterior border furrow deep, very wide (exsag.), ex-panding abaxially.

The rostral plate and hypostome of Emuella polymera havebeen adequately described and illustrated by Pocock (1970, p.530, pl. 106, fig. 6).

Librigena small, up to 9.5 mm in length (including genalspine); width (tr.) 30%–40% length (excluding genal spine); lat-eral margin moderately curved, continuing evenly onto genalspine; posterior margin straight. Genal field of low convexity,width (tr.) approximately 50%–60% librigenal width. Lateral bor-der weakly to moderately convex, widening (tr.) posteriorly, wid-est at genal angle; lateral border furrow shallow, narrow (tr.). Pos-terior border weakly to moderately convex, short (tr.), narrow(exsag.), moderately expanding in width (exsag.) abaxially; pos-terior border furrow moderately shallow, wide (exsag.), forming

continuation of cranidial posterior border furrow. Genal spinelong, length 50%–60% librigenal length (including spine); broadbase, strongly tapering posteriorly, with gentle adaxial curvature.

Thorax with observed maximum of 48 segments, divided intoprothorax of six segments (T1–T6) and opisthothorax of an ob-served maximum of 42 segments. Axial furrows well defined,subparallel to slightly tapering posteriorly along prothorax. Axisof T1–T4 of equal width, axial ring width (tr.) approximately50%–60% width of segment, moderately convex; sagittal nodeson posteromedial edge of prothoracic axial rings poorly developedto obscure; articulating half-ring subtriangular in outline, equal inlength (sag.) to axial ring; T1–T4 pleurae directed laterally (per-pendicular to axial line), width (tr.) of pleura approximately 20%–25% width of prothoracic segment, projected horizontally to ful-crum, then slightly downsloping to pleural spine; anterior pleuralband of moderate convexity, slightly expanding abaxially, poste-rior pleural band relatively flat, slightly tapering abaxially; pleuralspine very short, nonfalcate (‘‘thorn-like’’), formed by lateral ex-tension of anterior pleural band; pleural furrow moderately deep,very wide (exsag.), terminating at base of pleural spine. T5 axialring slightly narrower (tr.) than T1–T4 axial rings; T5 pleuraslightly wider (tr.) than T1–T4 pleurae, directed posterolaterally;T5 anterior pleural margin with flange and projection at antero-lateral corner (Fig. 3.6); T5 anterior pleural band expands abax-ially; T5 posterior pleural band fused to anterior pleural band ofT6 (macropleural segment), line of fusion marked by weak furrow(Fig. 3.6). T6 macropleural, axial ring slightly narrower (tr.) thanT5 axial ring; pleura strongly directed posterolaterally; anteriorpleural band rapidly expanding abaxially to base of macropleuralspine, posterior pleural band considerably narrower (exsag.) thananterior pleural band, slightly tapering abaxially to base of ma-cropleural spine; macropleural spine extremely long, extending tolevel of pygidium; T6 pleural furrow deep, very wide (exsag.),extending onto base of macropleural spine. Axis of opisthothoraxmoderately tapers to pygidium (Fig. 3.3); opisthothoracic seg-ments considerably smaller (sag., exsag., tr.) than those of pro-thorax; pleurae directed posterolaterally, width (tr.) of pleurae rap-idly decreasing posteriorly; opisthothoracic pleural spinesrelatively longer than T1–T5 pleural spines (Fig. 3.5).

Pygidium minute; axis and pleural field poorly defined. Pygid-ial margin smooth. Entire surface of exoskeleton densely coveredby tiny granules.

Material examined.Holotype AUGDF16653; figured speci-mens AUGDF16643, 16645, 16649, 16654, SAMP40266, threeunregistered specimens in D. Simpson private collection; unfi-gured specimens AUGDF16642, 16647, 16648, 16651, 16658,16701, 16702.

Occurrence.Early Cambrian (late Botoman). White PointConglomerate, Cape D’Estaing section, Kangaroo Island, SouthAustralia (Pocock, 1970, text-figs. 1, 2).

Discussion.Some of the cranidial characters used by Pocock(1970) in his species diagnoses of Emuella are questionable.These include: 1) the path of the axial furrows (or glabella out-line); 2) development of the glabellar furrows; and 3) the devel-opment of the anterior border furrow.

Pocock (1970) described Emuella polymera as having axial fur-rows that converge evenly from the posterior margin to S3,whereas in E. dalgarnoi, the axial furrows converge strongly fromthe posterior margin to SO, then weakly converge to S3. However,specimens of E. polymera and E. dalgarnoi can display eithercondition. Furthermore, well-preserved specimens of E. polymera(Fig. 3.7, 3.10, 3.11) and E. dalgarnoi (Fig. 4.1, 4.4) exhibit axialfurrows that strongly converge anteriorly from the posterior mar-gin to S1, then gently converge between S1 and S3. The consid-erable amount of intrapopulational variation in the axial furrowsof Emuella is likely to be preservational, perhaps the result of


FIGURE 4—Emuella dalgarnoi Pocock, 1970. All specimens come from the type locality, Emu Bay Shale, Emu Bay, Kangaroo Island, South Australia;all specimens in dorsal view. 1–3, Holotype (AUGDF16659; Pocock, 1970, pl. 107, fig. 4), internal mold; 1, almost complete exoskeleton, 38; 2,enlargement of opisthothorax, 313; 3, enlargement of posterior portion of opisthothorax showing pygidium, 336; 4–6, paratype (AUGDF16661;Pocock, 1970, pl. 107, figs. 5, 6), latex cast; 4, complete cranidium, 38; 5, enlargement of left posterolateral corner of cranidium showing posteriorborder, border furrow, and sutural ridge, 312.5; 6, enlargement of anterior portion of cranidium showing the parafrontal band and granuloseornament of the exoskeletal surface, 313.5; 7, paratype (AUGDF16662), latex cast of almost complete exoskeleton, 35.5; 8, paratype(AUGDF16660; Pocock, 1970, pl. 107, fig. 3), latex cast of almost complete exoskeleton, 35.5.

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FIGURE 3—Emuella polymera Pocock, 1970. All specimens come from the type locality, White Point Conglomerate, west of Cape D’Estaing, KangarooIsland, South Australia; all specimens in dorsal view. 1, Holotype (AUGDF16653; Pocock, 1970, pl. 106, fig. 1), internal mold of almost completeexoskeleton, 39; 2, latex cast of almost complete exoskeleton (D. Simpson, private collection), 36; 3, 4, paratype (AUGDF16654), teratologicalspecimen previously illustrated by Pocock (1974, figs. 1, 2); 3, internal mold of partial exoskeleton, 311; 4, enlargement of posterior portion ofopisthothorax showing transitory pygidium, 327; 5, 6, paratype (AUGDF16649; Pocock, 1970, pl. 107, fig. 1), latex cast; 5, partially articulatedthorax, 34.5; 6, enlargement showing fusion of T5 and T6, 37; 7, internal mold of partially complete cephalon (unnumbered specimen associatedwith AUGDF16701), 34.5; 8, latex cast of almost complete exoskeleton (D. Simpson, private collection), 34.5; 9, internal mold of cranidium (D.Simpson, private collection), 39; 10, paratype (AUGDF16643; Pocock, 1970, pl. 106, fig. 2), internal mold of cephalon, 312.5; 11, paratype(AUGDF16645; Pocock, 1970, pl. 106, figs. 3, 4), latex cast of cranidium, 39; 12, internal mold of incomplete, partially articulated exoskeleton(SAMP40266), 311.


FIGURE 5—Balcoracania dailyi Pocock, 1970. Reconstruction in dorsalview.

lateral and/or dorsal compression, rather than representing inter-specific variation. Morphological variability in the axial furrowshas also been observed in Balcoracania (discussed below).

Pocock (1970) interpreted the glabellar furrows of Emuella po-lymera as being shallow and indistinct, and those of E. dalgarnoias being wide, shallow, and distinct. Unfortunately, these diag-noses are unreliable because the development of the glabellar fur-rows in specimens of Emuella is highly variable, as is the casefor Balcoracania (discussed below). This variability can be ob-served in specimens of both species of Emuella. For example, theholotype of E. polymera (AUGDF16653) has distinct, well-de-veloped transglabellar furrows (Pocock, 1970, pl. 106, fig. 1; Fig.3.1), whereas the paratype AUGDF16645 possesses faint trans-glabellar furrows (Pocock, 1970, pl. 106, fig. 3; Fig. 3.11). Similarexamples can be observed in specimens of E. dalgarnoi (Fig. 4.1,4.4, 4.7, 4.8).

The degree of curvature of the anterior cranidial border furrowwas also used (Pocock, 1970) as a diagnostic character for speciesof Emuella. Pocock noted that the anterior border furrow in E.polymera is ‘‘almost transverse,’’ whereas the furrow in E. dal-garnoi ‘‘curves to anterior.’’ The degree of curvature in the an-terior border furrow in either species of Emuella does not appearto be consistent. Some specimens of E. polymera display a trans-verse furrow (Fig. 3.1, 3.2, 3.7, 3.11), while others show varyingdegrees of curvature (Fig. 3.9, 3.10).

Pocock (1974, figs. 1, 2) illustrated a complete specimen ofEmuella polymera (Fig. 3.3, 3.4). He interpreted the pygidium asbeing transitory, with seven axial rings and a terminal piece (Po-cock, 1974, fig. 3). On examination of the specimen(AUGDF16654), we agree with Pocock’s (1974) interpretation.The most mature known pygidia of E. dalgarnoi (Fig. 4.3) havefour axial rings.

EMUELLA DALGARNOI Pocock, 1970Figure 4

Emuella dalgarnoi POCOCK, 1970, p. 532, pl. 107, figs. 3–6.

Revised diagnosis.Width of posterior cranidial margin ab-axial to intergenal angle 80%–90% its width adaxial to intergenalangle; sutural ridge on posterior section of facial suture well de-veloped; anterior sections of facial suture diverging anteriorly at408–508 between g and b; palpebral lobe length (exsag.) 23%–27% cranidial length (sag.); eye ridges diverging posteriorly at1158–1308; posterior cranidial border furrow deepening abaxial tointergenal angle.

Material examined.Holotype AUGDF16659; figured speci-mens AUGDF16660–16662.

Occurrence.Early Cambrian (late Botoman). Emu Bay Shale,Emu Bay section, Kangaroo Island, South Australia (Pocock,1970, text-figs. 1, 2).

Genus BALCORACANIA Pocock, 1970

Type species.Balcoracania dailyi Pocock, 1970, Early Cam-brian, White Point Conglomerate, Kangaroo Island, South Aus-tralia; by original designation.

Revised diagnosis.Cephalon semicircular in outline; width(tr.) of posterior margin abaxial to intergenal angle 40%–50% itswidth adaxial to intergenal angle; anterior sections of facial suturediverging anteriorly at 558–708 between g and b; preglabellar fieldshort (sag.); palpebral lobe length (exsag.) 28%–33% cranidiallength (sag.), anterior tip of lobe situated opposite L3, posteriortip of lobe situated opposite L1; thorax with an observed maxi-mum of 103 segments (97 opisthothoracic segments); width (tr.)of prothoracic axis 40%–50% width of prothoracic segment.

BALCORACANIA DAILYI Pocock, 1970Figures 5–8

Balcoracania dailyi POCOCK, 1970, p. 533, pl. 108, figs. 1–8; pl. 109,figs. 1–6; pl. 110, figs. 19–22.

Balcoracania flindersi POCOCK, 1970, p. 535, pl. 109, figs. 7, 8; pl. 110,figs. 1–15.

Description.Cephalon moderately small, largest specimen(SAMP14570) with sagittal length of 8.0 mm; semicircular inoutline; low convexity (sag., tr.). Cranidium subquadrate in out-line; sagittal length approximately 80%–90% width (tr.) of pos-terior margin; anterior margin strongly curved; posterior margin(excluding occipital ring) straight, directed slightly posterolater-ally abaxially to intergenal angle (1358–1458), then strongly di-rected anterolaterally, width (tr.) of posterior margin abaxial tointergenal angle 40%–50% its width adaxial to intergenal angle.


FIGURE 6—Balcoracania dailyi. All specimens come from the type locality, White Point Conglomerate, west of Cape D’Estaing, Kangaroo Island,South Australia; all specimens in dorsal view. 1, Holotype (AUGDF16663; Pocock, 1970, pl. 108, fig. 1), latex cast of almost complete exoskeleton,38; 2, paratype (AUGDF16678; Pocock, 1970, pl. 109, fig. 2), latex cast of almost complete exoskeleton, 38; 3, latex cast of complete cephalonand partial prothorax (SAMP35525), 36; 4, latex cast of incomplete, partially articulated thorax (AMF98357), 38; 5, internal mold of incompleteexoskeleton (SAMP35511), 36; 6, latex cast of incomplete exoskeleton (SAMP35522), 38.5; 7, paratype (AUGDF16665; Pocock, 1970, pl. 108,figs. 2, 3), latex cast of complete cranidium showing well-developed plectrum, 38.5; 8, latex cast of complete cranidium showing well-developedfossulae (AMF98291), 312; 9, internal mold of complete cranidium (AMF98319), 310.5; 10, internal mold of incomplete cranidium showingwell-developed plectrum and parafrontal band (AMF98280), 310.


FIGURE 8—Balcoracania dailyi. All specimens from the Warragee Member, Billy Creek Formation, Flinders Ranges, South Australia, unless otherwisestated. All specimens in dorsal view. 1, 2, Almost complete exoskeleton (SAMP14559) from the Coads Hill Member, Billy Creek Formation,Reaphook Hill, South Australia; 1, latex cast, 35; 2, enlargement of internal mold showing articulating flange and anterolateral projection on T5anterior pleural margin, 317; 3, holotype of Balcoracania flindersi Pocock, 1970 (AUGDF16683; Pocock, 1970, pl. 109, fig. 7), internal mold ofalmost complete exoskeleton showing dorsal imprint of in situ hypostome, 37.5; 4, paratype of Balcoracania flindersi (AUGDF16681), latex castof almost complete exoskeleton, 34.5; 5, SEM image of latex cast of early meraspid showing interocular furrows and transitory pygidium(unnumbered specimen associated with AUGDF16687), 343; 6, SEM image of latex cast of meraspid cranidium (unnumbered specimen associatedwith AMF98280) from the White Point Conglomerate, west of Cape D’Estaing, Kangaroo Island, South Australia, 343; 7, SEM image of latexcast of meraspid cranidium (AUGDF16697; Pocock, 1970, pl. 110, fig. 12), 333.

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FIGURE 7—Balcoracania dailyi. All specimens from the Coads Hill Member, Billy Creek Formation, Reaphook Hill, South Australia. 1, Latex castof almost complete cephalon and partial prothorax (SAMP14570), dorsal view, 34.5; 2–6, latex cast of an incomplete, partially disarticulatedthorax showing opisthothorax of at least 97 segments (SAMP14556); 2, dorsal view, 37; 3, enlargement of posterior portion of opisthothorax,dorsal view, 311.5; 4, SEM image showing posterior portion of opisthothorax and pygidium, dorsal view, 353; 5, oblique lateral view, 37.5; 6,SEM image of posterior portion of opisthothorax and pygidium, dorsal view, 323; 7, latex cast of complete exoskeleton showing opisthothoraxof at least 69 segments (SAMP14560), dorsal view, 39.5; 8, latex cast of almost complete exoskeleton (SAMP14568), dorsal view, 39.

Anterior sections of facial suture diverging anteriorly at 558–708between g and b, then strongly converging between b and a.Posterior sections of facial suture very short, diverging posteriorlyat 908 between « and v. Glabella gently tapering anteriorly fromposterior margin to S1, subparallel between S1 and S3, then ex-panding into frontal lobe; frontal lobe broadly rounded with shal-low median depression in anterior margin, width (tr.) 73%–85%width of LO; moderately convex (tr.); sagittal length (includingLO) 80% cranidial length. Axial furrow shallow and of moderatewidth (tr.); fossula at junction of posterolateral corner of frontallobe and anterior margin of eye ridge variably developed, rangingfrom obscure to small, discrete pit; preglabellar furrow weakly

developed. S1 weakly to moderately impressed, transglabellar, ab-axial portions directed slightly posteromedially, becoming trans-verse sagittally; S2 and S3 weakly to moderately impressed, trans-glabellar, transverse. Occipital ring moderately convex (tr.), length(sag.) approximately 18% cranidial length; anterior marginstraight; posterior margin bowed posteriorly; faint posteromedialoccipital node. SO straight, moderately wide (sag., exsag.), deepacross its entire width. Preglabellar field very short, length (sag.)5%–10% cranidial length; plectrum weakly developed and of lowrelief, slightly narrower (tr.) than frontal glabellar lobe. Preocularfixigenal field gently downsloping anteriorly, flat to gently con-vex, length (exsag.) approximately 20% cranidial length (sag.).


Anterior border flat to weakly convex, length (sag.) 11%–15%cranidial length, strongly tapering (exsag.) abaxially; anterior bor-der furrow narrow (sag., exsag.), well developed laterally, shallowmedially where posterior margin of border extends back to formplectrum. Palpebral lobe well developed, strongly convex, length(exsag.) 28%–33% cranidial length (sag.), width 34%–38% lobelength, anterior tip situated opposite L3, posterior tip situated op-posite L1; palpebral furrow shallow, moderately wide (tr.). Eyeridge well developed, forming continuation of palpebral lobe, flatto weakly convex (exsag.), straight distally before being directedanteriorly near axial furrow, ridges diverge posteriorly at 1158–1258; eye ridge divided into inner and outer bands by weaklydeveloped ocular furrow, inner band merges with posterolateralportion of frontal glabellar lobe, outer band continues around an-terior margin of frontal lobe to form weakly developed parafrontalband. Palpebral area moderately convex, width at « (tr.) 70%–80% adjacent glabellar width. Postocular area very short (exsag.).Posterolateral projection of fixigena very short (tr.), gently down-sloping, strongly tapers abaxially. Posterior border moderatelyconvex (exsag.), slightly expanding abaxially to intergenal angle,then tapers to distal end of border; posterior border furrow deep,wide (exsag.), expanding abaxially.

The rostral plate and hypostome of Balcoracania dailyi havebeen adequately described and illustrated by Pocock (1970, p.535, pl. 109, figs. 4, 5).

Librigena small, up to 11 mm in length (including genal spine);width (tr.) approximately 35%–40% length (excluding genalspine); lateral margin moderately curved, continuing evenly ontogenal spine; posterior margin straight. Genal field of low convex-ity, width (tr.) approximately 50%–55% librigenal width. Lateralborder flat to weakly convex, widening (tr.) posteriorly, becomingwidest at genal angle; lateral border furrow shallow, narrow (tr.).Posterior border flat, short (tr.), narrow (exsag.), moderately ex-panding in width (exsag.) abaxially; posterior border furrow mod-erately shallow, wide (exsag.), forming continuation of cranidialposterior border furrow. Genal spine long, length 55%–65% li-brigenal length (including spine); broad base, strongly taperingposteriorly, slight adaxial curvature. Several closely spaced ter-race ridges developed on lateral and posterior portions of libri-genal doublure.

Thorax with observed maximum of 103 segments, divided intoprothorax of six segments (T1–T6) and opisthothorax of an ob-served maximum of 97 segments (Fig. 7.2–7.6). Axial furrowswell defined, subparallel along prothorax. Axis of T1–T4 of equalwidth, axial ring width (tr.) approximately 40%–50% width ofsegment, moderately convex; T1–T4 pleurae directed laterally(perpendicular to axial line), width (tr.) of pleura approximately25%–30% width of prothoracic segment, projected horizontallyto fulcrum, then slightly downsloping to pleural spine; anteriorpleural band of moderate convexity, slightly expanding abaxially,posterior pleural band relatively flat, slightly tapering abaxially;pleural spine very short, nonfalcate (‘‘thorn-like’’), formed by lat-eral extension of anterior pleural band; pleural furrow moderatelydeep, very wide (exsag.), terminating at base of pleural spine. T5axial ring slightly narrower (tr.) than T1–T4 axial rings; T5 pleuraslightly wider (tr.) than T1–T4 pleurae, directed posterolaterally;T5 anterior pleural margin with flange and projection at antero-lateral corner (Fig. 8.2); T5 anterior pleural band expanding abax-ially; T5 posterior pleural band fused to anterior pleural band ofT6 (macropleural segment), line of fusion generally indistinct,marked by weak furrow (Figs. 6.2, 6.3, 7.8, 8.3) or completelyeffaced (Figs. 6.1, 6.4–6.6, 7.7, 8.1). T6 macropleural, axial ringslightly narrower (tr.) than T5 axial ring; pleura strongly directedposterolaterally; anterior pleural band rapidly expanding abaxiallyto base of macropleural spine, posterior pleural band considerablynarrower (exsag.) than anterior pleural band, slightly tapering

abaxially to base of macropleural spine; macropleural spine ex-tremely long, extending to level of pygidium; T6 pleural furrowdeep, very wide (exsag.), extending onto base of macropleuralspine, then becoming shallow and narrow along length of spine.Axis of opisthothorax moderately tapers from macropleural seg-ment to about midlength of opisthothorax, then subparallel to py-gidium (Fig. 7.7); opisthothoracic segments considerably smaller(sag., exsag., tr.) than those of prothorax; pleurae directed pos-terolaterally, width (tr.) of pleurae rapidly decreasing posteriorly;opisthothoracic pleural spines relatively longer than T1–T5 pleu-ral spines.

Pygidium minute, parabolic in outline, slightly longer thanwide; margin entire; without distinct division into axis and pleuralfield in preserved specimens (Fig. 7.2–7.7); first segment weaklydefined by shallow transverse furrow.

Entire surface of exoskeleton densely covered by tiny granules.Material examined.Holotype AUGDF16663; figured speci-

mens AUGDF16665, 16678, 16681, 16683 (holotype of B. flin-dersi), 16697, SAMP14556, 14559, 14560, 14568, 14570, 35511,35522, 35525, AMF98291, 98319, 98357; unfigured specimensAUGDF16655, 16664, 16666, 16667, 16669, 16671, 16673,16676, 16679, 16680, 16687–16696, 16698–16700, 16703–16706, SAMP14543–14555, 14557, 14558, 14561–14567, 14569,14571, 35510, 35512, 35516, 40265, 40267–40276, AMF98278–98290, 98292–98318, 98320–98356, 98358–98371.

Occurrence.Early Cambrian (late Botoman). White PointConglomerate, Cape D’Estaing and Emu Bay sections, KangarooIsland, South Australia (Pocock, 1970, text-figs. 1, 2); WarrageeMember, Billy Creek Formation, Flinders Ranges, South Australia(Pocock, 1970, text-fig. 1; Moore, 1979, figs. 2–4); Coads HillMember, Billy Creek Formation, Reaphook Hill, South Australia(Moore, 1980).

Discussion.Pocock (1970) differentiated Balcoracania flin-dersi from B. dailyi based on the following cranidial characters:1) path of the axial furrows (or glabellar outline); 2) absence ofa preglabellar field; 3) absence of anterior border fossulae; and4) well-developed transglabellar furrows. These morphologicalfeatures represent rather dubious diagnostic characters, since theyare highly variable in specimens from the same locality/popula-tion and are thus likely to be the result of intraspecific variationor preservation. It should be noted that strata at each emuellidlocality (e.g., Kangaroo Island, Balcoracana Creek, and ReaphookHill) have undergone varying degrees of tectonic deformation(Gravestock, 1995; Priess, 1999; and references therein), thus in-fluencing the preservation of some specimens.

Pocock (1970, p. 536) noted that the cranidial axial furrows ofBalcoracania flindersi ‘‘converge evenly from posterior marginto anterior glabellar furrow [5 S3], then curve out and aroundmarkedly expanded frontal glabellar lobe.’’ The holotype, para-types, and majority of topotype specimens of Balcoracania dailyifrom the White Point Conglomerate, west of Cape D’Estaing,Kangaroo Island, display axial furrows that gently taper anteriorlyfrom the posterior margin to S1, become subparallel between S1and S3, then curve around an expanded frontal lobe, as noted byPocock (1970). However, the axial furrows of some topotypecranidia of B. dailyi display the B. flindersi condition (Fig. 6.8,6.9). Both conditions can likewise be observed in cranidia fromthe Warragee Member and Coads Hill Member of the Billy CreekFormation at Balcoracana Creek and Reaphook Hill, respectively.Therefore, the variation in the axial furrows of Balcoracania cran-idia is likely to be preservational, perhaps relating to lateral and/or dorsal compression.

The presence or absence of a preglabellar field in cranidia ofBalcoracania is related to ontogeny, rather than representing aninterspecific variant. Examination of Balcoracania specimensfrom each locality, including type material, reveals that cranidia


with a sagittal length of less than 2.8 mm do not exhibit a preg-labellar field. Larger cranidia (Fig. 7.1) display a short pregla-bellar field up to 10% of cranidial length (sag.). It is also impor-tant to note that cranidia exhibiting a well-preserved plectrumand/or parafrontal band often create the illusion that the pregla-bellar field is absent.

Pocock (1970) noted that in Balcoracania dailyi, specimensthat exhibit a medially ‘‘raised’’ anterior border furrow (5plec-trum) possess distinct ‘‘anterior border fossulae’’ (see his text-fig.4.1). Pocock (1970, pl. 108, fig. 5) illustrated a small cranidium(sagittal length: 3.5 mm) of B. dailyi showing what appear to beanterior border fossulae; however, examination of other cranidiain the type series and additional topotype cranidia of B. dailyireveals no such feature.

The development of the glabellar furrows in the cranidia ofBalcoracania varies considerably. Pocock (1970) described B.dailyi as having transglabellar furrows that are distinct abaxially,but shallow and indistinct sagittally, and B. flindersi as havingdistinct, deep transglabellar furrows. These diagnostic morphol-ogies are inconsistent among cranidia from each locality/popula-tion. For example, the type series and topotype cranidia of B.dailyi can display transglabellar furrows that are: 1) almost com-pletely effaced (Fig. 6.2, 6.7); 2) variably developed laterally, butindistinct sagittally (Fig. 6.8, 6.9); or 3) of equal depth across theentire glabella (Fig. 6.1, 6.5, 6.6). The latter condition is the mostcommon and is displayed by the better-preserved cranidia, and istherefore likely to represent the actual morphology of the glabellarfurrows.

Balcoracania dailyi (5B. flindersi) was previously known tohave as many as 61 thoracic segments (Pocock, 1970), the max-imal number known for any trilobite (Whittington, 1997, p. 43).The specimen in Figure 7.2–7.6 has 103 segments, including 97segments in the opisthothorax, representing a new record in tri-lobite segmentation. It is possible that emuellids grew by addingsegments throughout their lives without a fixed terminal numberof segments (euanamorphosis as defined by Minelli et al., 2003,p. 37), as has been speculated for other Cambrian trilobites withvery high and intraspecifically variable numbers of thoracic seg-ments (Minelli et al., 2003). Euanamorphosis could account forthe relatively enhanced degree of variability in thoracic segmentnumbers in early members of the Trilobita (McNamara, 1983;Hughes et al., 1999). It is clear that the prothorax in emuellidsattains a fixed terminal number of six segments (including themacropleural segment). However, the number of segments in theopisthothorax shows considerable plasticity, as is evident in spec-imens of Balcoracania dailyi that possess a complete opisthoth-orax and articulated pygidium (Fig. 7.2–7.7). It is important tonote that these specimens vary in size. The smaller specimen (Fig.7.7) has a cephalic length (sag.) of 3.4 mm and displays 69 op-isthothoracic segments. The specimen with 97 opisthothoracicsegments (Fig. 7.2–7.6) is 1.5 times larger, based on the axial ringwidth (tr.) of T6. Unfortunately, it is impossible to determinewhen (or if) the segment accretion phase terminates in emuellidswithout conducting a quantitative meristic analysis on a largenumber of complete specimens, such as that of Hughes and Chap-man (1995).

ACKNOWLEDGMENTS

We are indebted to D. Simpson, J. Gehling, and J. Jago fordonating excellent emuellid specimens from their personal col-lections to assist our study. Thanks to J. Gehling and D. Rice,who provided invaluable assistance to JRP during visits to theSouth Australian Museum in 2003 and 2004, and for arrangingthe loan of type and other specimens in their care. We thank C.Nedin for guiding collecting with GDE at Cape D’Estaing, A.Lam for inking Figure 5, and P. Ahlberg and B. Lieberman for

their reviews. Funding for this study came from a Macquarie Uni-versity Postgraduate Research Fund grant to JRP.

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