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Cretaceous Research 32 (2011) 407e421

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Cretaceous Research

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Mathesia darderi (Astre) (Bivalvia, Hippuritoidea, Monopleuridae): Morphological,biogeographical and ecological changes in the Mediterranean domain during thelate BarremianeAlbian

M. Fenerci-Masse a, J.-P. Masse a,*, B. Ko1odziej b, M. Ivanov c, V. Idakieva c

aGéosystèmes carbonatés, Université de Provence, Marseille, Franceb Institute of Geological Sciences, Jagiellonian University, Kraków, PolandcDepartment of Geology and Paleontology, Sofia University, Bulgaria

a r t i c l e i n f o

Article history:Received 15 March 2010Accepted in revised form 22 October 2010Available online 26 November 2010

Keywords:BivalviaMonopleuridaeBarremianeAlbianPhyletic size increaseMediterranean

* Corresponding author.E-mail addresses: Jean-Pierre.Masse@univ-proven

kolodziej@uj.edu.pl (B. Ko1odziej), mivanov@geaidakieva@gea.uni-sofia.bg (V. Idakieva).

0195-6671/$ e see front matter � 2010 Published bydoi:10.1016/j.cretres.2010.10.005

a b s t r a c t

Mathesiadarderi, a slender cylindricalmonopleuridgenus, formerlydocumented fromthe lateAptianeAlbianof Spain, France, Tunisia, Algeria, Egypt andTurkey, hasbeendiscovered in theupperBarremianand the lowerAptian of Bulgaria and Spain.Notwithstanding somemorphological changes, BarremianelowerAptian formsand those of the upper AptianeAlbian possess the same myocardinal organisation and the same micro-structural attributes. The inner shell margin of the right valve displays scalloped, festooned, tubular andvermiformmicrostructures. The most prominent evolutionary trait ofM. darderi is the increase in body sizethrough time. A statistical analysis of size distributions show that populations of the late BarremianeearlyAptian, and the late Aptian, and those of the early tomiddle Albian, are significantly different; a patternwhichhas a biostratigraphic potential. Ecological changes through time are expressed by a displacement ofcommunities from the central/distal part, to the proximal part of carbonate platforms. M. darderi ispresent locally in the upper Barremianelower Aptian, and has its major spreading over the European andAraboeAfrican margins of the Mediterranean Tethys during the Clansayesianelower to middle Albian. Thedisappearance of the species at the MiddleeUpper Albian boundary, correlates with a critical, spatialreduction of carbonate platforms.

� 2010 Published by Elsevier Ltd.

1. Introduction

Monopleurid rudists tend to play a limited physiognomic role inEarly Cretaceous shallow water carbonate platforms of the Medi-terranean region. Instead the Requieniidae are usually the majorcontributors to “rudist formations” (Masse and Philip, 1981).Nevertheless tubular Monopleuridae, having an elevator morpho-type (in the sense of Skelton and Gili, 2002), are locally abundantand may have a significant constructional potential especiallyduring the early Valanginian and the late AptianeAlbian (Fenerci-Masse, 2006), Mathesia darderi (Astre) being a key species in thisrespect (Fenerci-Masse, 2006; Masse and Fenerci-Masse, 2010).

Mathesia was hitherto considered to be represented by a singlespecies, M. darderi, and restricted to the upper AptianeAlbian ofthe northern and southern margins of the Mediterranean Tethys.

ce.fr (J.-P. Masse), boguslaw..uni-sofia.bg (M. Ivanov),

Elsevier Ltd.

The objectives of the present paper are to describe representativesof M. darderi, found in the upper Barremian of the Fore-Balkanarea (Bulgaria) and the Prebetic area (SE Spain), the lower Aptian ofNE Spain (Maestrat), and compare themwith upper AptianeAlbianforms.

Then we address the morphological changes of the speciesthrough time, based on qualitative and quantitative analysis,focusing on size increase and its biostratigraphic implications.Finally we discuss associated palaeobiogeographical and palae-oecological changes from the Barremian to the middle Albian,and the question of the origination and demise of the specieswith special attention paid to the corresponding environmentaldeterioration.

2. Systematic palaeontology

Abbreviations: LV, left valve; RV, right valve; D, dorsal side;V, ventral side;A, anterior side; P, posterior side;BC, bodycavity; amb,anterior myophoral bulge; pm, posterior myophore; pmp, posteriormyophoral plate; at, anterior tooth; ct, central tooth; t, tooth; as,

Fig. 1. Types of microstructures of the inner margin of the outer shell layer (transverse section) of Albian representatives of Mathesia darderi. (A) bilamellar structure, notice the flatboundary with the inner shell layer; (B) tightly linked adjacent sub-rounded bodies with a fan-like fibrous structure responsible for the scalloped aspect of the boundary betweenthe outer and inner shell layer (f), flanked outward by radial fibres (r) (polarized light), arrow points to body cavity; (C) deeply scalloped (festoons) inner margin; (D) same withminute tubes; (E) double row of minute tubes; (F) same to show the radial orientation of tubes; (G) longitudinal oblique section showing the connection between the inner, tubular,and outer, compact, portions of the outer shell layer; (H) longitudinal, tangential, section of the inner scalloped portion of the outer shell layer showing the elongated structureswith a feather-like microstructure, distal (commissural) terminations acute; (I) close up of (H) showing diverging fibres from a median dark line. Figures (A, C, D, E, F, G) are fromspecimens of Sierra del Carche (SE Spain), figures (B, H, I) are from specimens of Barbaros, Karaburun Peninsula (Western Turkey).

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Fig. 2. Geographical map and location of late Barremian Mathesia-bearing localities in the Central Fore-Balkan domain of Central Northern Bulgaria.

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anterior socket; ps, posterior socket; L, ligament ridge; Lac, anteriorligament cavity; Lpc, posterior ligament cavity; tab, tabulae; AB,anterior band; PB, posterior band.

Order: Hippuritoida Newell (1965)Superfamily: Hippuritoidea Gray (1848)Family Monopleuridae Munier-Chalmas (1873)Mathesia Mainelli (1996) emend. Masse and Fenerci-Masse.Type species: Mathesia darderi (Astre)

1933 e Agria darderi Astre (1933), p. 103, text-figs.1-51954 e Agria darderi var. pyrenaica, Astre (1954), pl. V, fig. 1,text-fig. 191974 e Agriopleura darderi (Astre), Masse and Philip (1974),figs. 2-3.1983 e Agriopleura darderi (Astre), Chikhi-Aouimeur (1983),p. 43, pl. 2, fig. 6.1992 e Agriopleura? darderi (Astre), Masse et al. (1992), p. 206,pl.4, fig. 61995 e Agriopleura, Cestari and Sartorio (1995), p. 95, 97,text-figs.1996 e Mathesia tertiicolloquiirudistarum Mainelli (1996),p. 201-209, pl. 1, fig. 1-13; pl. 2, fig. 1-10; fig. 4; pl. 3, fig. 1-4.1998ae Agriopleura? darderi (Astre), Masse et al. (1998a), p. 201,fig. 10-12002 e Agriopleura? darderi (Astre), Steuber and Bachmann(2002), p.736-738, text-fig. 7 E-F, plate1, Fig. 1.2010 e Mathesia darderi (Astre), Masse and Fenerci-Masse(2010), fig. 2, p. 549, fig.4, p. 550, fig. 5, p. 546, fig. 6, p. 551.

2.1. Characters of M. darderi

The recent reappraisal of “Agria” darderi Astre (Astre, 1933) andMathesia tertiicolloquiirudistarum Mainelli (Mainelli, 1996), basedon late AptianeAlbian specimens, has shown that these two formsrepresent a single taxonomic entity M. darderi (Astre) (Masse and

Fenerci-Masse, 2010). The diagnosis is as follows: cylindro-conicalelongated RV (right valve), moderately salient (capuloid, posterio-rily flattened) LV (left valve); outer shell layer with a scalloped ortubular inner margin; LV with an erect posterior myophoral plate,the anterior myophore a crest or a bulge; myophores of RV on shellwall; ligamental ridge small, in a cavity; radial bands flat or slightlyconcave.

Four main basic microstructures have been recognized, intransverse sections, at the inner margin of the outer shell layer (i.e.calcitic layer) of the RV, (Fig. 1):

(1) Radial fibrous, bilamellar, a feature commonly found in theMonopleuridae (Masse and Philip, 1974), the boundary withthe inner shell layer (formerly aragonitic) is nearly flat (Fig. 1A),

(2) Semi-rounded bodies having a fan-like arrangement of prisms intransverse section, corresponding with a convex inward scal-loped outline; usually there is a single row of semi-roundedbodies, flanked outward by radial prisms (Fig. 1B,C),

(3) Loosely packed convex inward protrusions, separated by sub-rounded or pyriform cavities (Masse and Philip, 1974), theinvagination of the inner shell layer tends to produce deepfestoons (Fig. 1DeF),

(4) Folded protrusions may result in the formation of two rows,or sometimes more, sub-rounded cavities, the orientation ofwhich tend to be longitudinal to the shell axis (main tubes) oreven oblique to the shell axis to form minute somewhatvermiform features (Fig. 1GeI).

As stated earlier (Masse and Fenerci-Masse, 2010) thepeculiar microstructure on the inner margin of the outer shelllayer is expected to correspond with radial crenulations of theinner marginal growth surface, a feature which may correspondto the impressions of bundled radial pallial muscles of theretractable outer mantle lobe, inside the inner shell surface(Skelton, 1976 and personal communication, following Jaworski,1928).

Fig. 3. Stratigraphic setting of ammonite and Mathesia-bearing localities of the BarremianeBedoulian Lovetch Urgonian Group in the Central Fore-Balkan domain of CentralNorthern Bulgaria. 1eTrambesh Fm. (Lower Aptian); 2eRoman Fm. (Lower Aptian); 3ePavlikeni Fm. (lowermost Aptian); 4eGorna Oryahovitsa Fm. (Lower BarremianelowermostAptian); 5eDevetaki Fm. (Lower Aptian); 6eSmochan Fm. (Upper BarremianeLower Aptian); 7eStratesh Fm. (Upper Barremian); 8eByala Reka Fm. (Upper Barremian); 9eEmenFm. (LowereUpper Barremian); 10eBalgarene Fm. (LowereUpper Barremian); 11eMathesia localities: Hotnitsa-ecotrack (A); Rusalya quarry (B); Vishovgrad quarry (C); 12eammonite localities: Samovodene (a); Hotnitsa-“Rimski pat” (b); Mihaltsi quarry (c); Dichin quarry (d); Paskalevets (e).

Fig. 4. Geographical and stratigraphical settings ofMathesia-bearing beds from SE Spain. A-location map showing the reference section of Sierra de la Muela. B-stratigraphic sectionof the BarremianeAptian p.p. to illustrate the position of Mathesia-bearing beds.

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2.2. Geographical and stratigraphical settings of BarremianelowerAptian Mathesia-bearing beds

This section addresses the geographical location and strati-graphical context of specimens ofMathesia from Bulgaria and Spain.

2.2.1. BulgariaRepresentatives of Mathesia have been collected from the

Emen Formation, the middle part of the Lovetch Urgonian Groupin the Central Fore-Balkan domain of the Central NorthernBulgaria (Figs. 2 and 3). The Barremianelower Aptian LovetchUrgonian Group consists of four terrigenous and four inter-bedded carbonate formations (Khrischev, 1966; Nikolov, 1969;Peybernès et al., 1979; for review see Minkovska et al., 2002;Nikolov et al., 2007) (Fig. 3). In the Emen Formation bioclasticsand coral-rich beds are the dominant facies; rudist occurrencesare uncommon or have a limited local extent (Minkovska, 1996).By contrast, in the overlying limestones of the Stratesh Forma-tion, rudists tend to play a significant physiognomic role,Requieniidae being the key elements, that is Lovetchenia andToucasia are dominant over other forms (Zlatarski, 1886;Atanassova-Deltcheva, 1978; Masse, 1993).

Fig. 5. Microscopic structures of Mathesia darderi from the late Barremian (Fore-Balkan, Bulthe minute tubes flanking the inner shell margin. B-anterior side, left shell: irregular festoowith a compact fibrous structure.

In the study area the Emen Formation grades laterally to theGorna Oryahovitsa Formation, and consists of two tonguesbracketed by marly units with ammonites, the stratigraphicsignificance of which matches the reference zonation of Rebouletet al. (2009).

The lower tongue (Fig. 3) overlies marly beds with Holcodiscusfallax and H. irregularis, which mark the Kotetishvilia com-pressissima Zone (lower Barremian) (Ivanov and Nikolov,1995), andis overlain by marls of the Balgarene Formation with Holcodiscusdiversecostatus, H. geronimaeformis, Astieridiscus elegans andAstierodiscus cf. cadoceroides (Ivanov and Nikolov, 1995); nearHotnitsa these marls yield Barremites difficilis, Barrancyloceras aff.barremense, Artaerites sp. and Protetragonites crebsisulcatus, anassociation indicative of the Toxancyloceras vandenhecki Zone(lowermost Upper Barremian) (Ivanov and Idakieva, 2009). Theupper tongue (Fig. 3) overlies the Balgarene marls and is overlainby marls of the Byala Reka Formation and/or their lateral equi-valent of the Gorna Oryahovitsa Formation; which also containBarremian ammonites, including Barremites difficilis, Barremites sp.and Cassidoiceras sp.

Upper Barremian ammonites, belonging to the Imerites giraudiZone are found near the top of the Gorna Oryahovitsa Formation,

garia). Transverse sections. A-dorsal side showing the triangular ligament ridge, noticens, right shell: fine tubes. C-ventral ribs and scalloped microstructure. D-posterior side

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a lateral equivalent of the Smochan Formation (overlying theStratesh limestones) (Khrischev, 1992; Ivanov, 1995, Stoykova andIvanov, 2000, Ivanov and Idakieva, 2009).

Three localities with Mathesia have been identified: Hotnitsa,Rusalya and Vishovgrad. The first one is located within the lowertongue of the Emen Formation and the two others in the uppertongue; the position of the Vishovgrad site being close to the topof the Emen limestones.

The foregoing shows that Mathesia collecting sites range fromthe Toxancyloceras vandenhecki zone, up to the Gerhardtia sar-tousiana zone, that is essentially the lower part of the upper Bar-remian (though its presence in the underlying, latest earlyBarremian Moutoniceras moutonianum zone cannot be ruled out).

2.2.2. SE SpainMathesia-bearing beds have been discovered at Sierra de la

Muela, in the vicinity of Benizar (Murcia Province) (Fig. 4A,B). Thecorresponding stratigraphic section formerly studied by Fourcadeet al. (1972) has been recently reappraised by a team of workersfrom the Jaen and Madrid universities including one of us (JPM)(work in progress). Mathesia-bearing beds are present in theupper part of rudist (Requieniidae, Monopleuridae)-rich pack-stones and wackestones with Montiella cf. benizarensis (Fourcadeet al.), Salpingoporella piriniae Carras and Radoicic, Halimedacea,Choffatella decipiens Schlumberger, Neotrocholina? aptiensis(Iotcheva), Orbitolinopsis gr. cuvillieri-kiliani Prever and Orbitoli-nopsis aff. buccifer Arnaud-Vanneau and Thieuloy, ascribed to theuppermost Barremian. Underlying beds consist of marls anddasycladale-rich limestones characterized by Falsolikanella dan-ilovae (Radoicic), a Barremian marker. Beds overlying the Mathe-sia-bearing beds consist of orbitolinid-rich, nodular marlylimestones with quartz, with Orbitolinopsis kiliani Prever andPalorbitolina lenticularis (Blumenbach) ascribed to the lowerAptian.

Fig. 6. Mathesia darderi from the late Barremian (Fore-Balkan, Bulgaria). Dorsal side showingCeD e the wall bounding the posterior socket from the posterior ligament cavity was not

2.2.3. NE SpainMathesia has been recently identified by P.W. Skelton (personal

communication) in lower Aptian limestones of the Maestratbasin; the corresponding beds yield Caprina parvula Douvillé andO’Gorman, Polyconites hadriani Skelton et al. and Iraqia simplexHenson, ascribed to the Furcata zone (uppermost Bedoulian)(Skelton et al., 2010; Bover-Arnal et al., 2010)

2.3. Characters of Barremian Mathesia

This section addresses the description of specimens of Mathesiacollected in Bulgaria and Spain.

2.3.1. Specimens from BulgariaThe study material consists of slabs and thin sections cut in

rock samples, including several tens of specimens usuallypreserved in life position and aggregated in clusters or thickets,closely associated with minute phaceloid corals belonging to thesuborder Pachythecaliina (Kolodziej et al., 2009), a group assignedby some authors to the order Hexanthiniaria and not Scleractinia(Eliá�sová, 1978; Roniewicz, 2008).

Transverse and longitudinal sections document the cylindricalhabit of the RV. Thin sections cut transversally into this valveshow the peculiar microstructure of the inner margin of the calciticouter shell layer, with a scalloped or festooned habit grading torounded cavities (sections of longitudinal tubes), usually in onerow, and passing to vermiform structures, especially in corre-spondence with ribs of the outer shell surface (Fig. 5). The ligamentcrest is triangular and located in a relatively wide cavity usuallysplit into two parts by a transverse septum extending ventrallyfrom the ligament crest, this wall separates two cavities (anteriorand posterior) adjacent to the sockets (Fig. 6). Sockets displayone or two inward protruding ridges which imply that the teeth ofthe opposite valve were ribbed. Sections of the LV show a salient

the ligament cavities and tooth sockets. AeB e the ligament is flanked by two cavities.preserved. Notice the ridges protruding into the tooth sockets.

Fig. 7. Mathesia darderi from the late Barremian (Fore-Balkan, Bulgaria). Longitudinal sections of the LV. A e B-dorsal section showing the myophores and the posterior tooth.C e ventral section showing the well preserved outer shell layer with ribs.

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protruding posterior myophoral plate and an anterior myo-phoral bulge; when preserved, the outer surface of the valve isribbed (Fig. 7). The radial bands are flat and flanked by obtuseribs (Fig. 5).

Fig. 8. Mathesia darderi from the late Barremian (Sierra de la Muela, SE Spain). Microstructurthe scalloped inner margin (compare with figures 1H and I). B-tubular and vermiform stru

2.3.2. Specimens from SE SpainThe study material consists of slabs and thin sections cut in rock

samples, including nearly twenty aggregated specimens. On trans-verse sections the inner margin of the calcitic outer shell layer of the

al aspects. A-oblique tangential section showing the striated aspect corresponding withctures. C-same. D-transverse oblique section of festoons.

Table 1Size parameters of specimens of Mathesia darderi from the Mediterranean region(Bulgaria, Spain, Algeria, Tunisia, Turkey and Italy).

Dorso-ventraldiameter (dDV)

Antero-posteriordiameter (dAP)

Averagediameter(dAver.)

Number of specimens 116 123 111Mean (cm) 1.4 1.2 1.3Standard deviation (cm) 0.4 0.4 0.4Min (cm) 0.6 0.5 0.65Max (cm) 2.9 2.2 2.4

Fig. 9. Box plot graph showing the variations of the average diameter of specimens ofMathesia darderi from the BarremianeAptian transition, the Upper Aptian and theLower to Middle Albian, to document size increase through time (see text forcomments).

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RV displays various aspects, including: scalloped, festooned andvermiform microstructures (Fig. 8BeD). Tangential sections of thesame margin illustrates that the longitudinal ribs correspond withthe festoons seen in transverse sections (Fig. 8A). The ligament ridgeis triangular. We didn’t find sections of the LV and the outer shellsurface of the RV is usually micritized, therefore the ornamentationwas not preserved.

In summary the peculiar microstructure of the inner margin ofthe outer shell layer of the RV of specimens from Bulgaria andSpain matches the diagnostic attributes of Mathesia in the sense ofMasse and Fenerci-Masse (2010), and the myophoral organisationof the LV (Bulgarian specimens) as well.

2.4. Relationships with the late AptianeAlbian Mathesia andimplications for the definition of M. darderi

Myocardinal features of specimens from the BarremianelowerAptian are similar to those of the late AptianeAlbian. Both possessscalloped, festooned or vermiform structures in the outer shelllayer of the RV. Tubular structures are less commonwhereas, in theBulgarian specimens they are obviously more developed than inthe Spanish specimens, a dissimilarity which suggests local, i.e.environmental, control. The irregular distribution of these variousmicrostructures within a given individual and within a populationis the most striking feature of Mathesia from the Barremian whichtherefore appears to be highly variable with respect to the micro-structural characters. As stated earlier for late AptianeAlbianforms (Masse and Fenerci-Masse, 2010), the relative developmentof the four basic types of microstructures tend to vary corre-sponding with the size of the specimens and, in a given specimen,corresponding with the different parts of the shell.

With such changes in variability distinguishing forms belongingto the Barremianelower Aptian from those of the upper Apti-aneAlbian, with associated size increase (see discussion below) itwould have been tempting to formalize these differences, that isto create a new specific taxonomic entity for the former specimens.The apparent Gargasian gap in the fossil record (see discussionbelow) might also have been used as a convenient means toseparate two potential chronospecies. However, the strong simi-larities between populations, their evident intergradations, and thedifficulty to assign a given specimen from a population to a givenpotential chronospecies lead us to include Barremianelower Aptianforms with those from the upper AptianeAlbian in a single species,M. darderi. The following quantitative analysis of patterns in sizedocuments the existence of three groups having each a specificstratigraphic distribution (see discussion below).

Assuming that Mathesia is monospecific, well preserved speci-mens from Bulgaria allow us to specify some characters whichwere poorly known or poorly illustrated in previous works, espe-cially concerning the cardinal area of the RV and the ornamentationof the LV; these characters are therefore significant attributes ofM. darderi. The cardinal area shows a subtriangular or quad-rangular posterior socket and an anterior subrectangular (radiallycompressed) socket (Fig. 6); radial ribs are present in the twosockets (Fig. 6), which means that the teeth of the LV are longitu-dinally ribbed, as in Petalodontia Pocta (Pocta, 1889) and Bicornu-copina Hofman (Masse, 1992). The reappraisal of some upperAptianeAlbian Spanish and Tunisian specimens matches the aboveobservations. The presence of ribs on the LV, already mentionedand illustrated by Mainelli (1996) from specimens of late Aptianage, was ignored in the reappraisal of Mathesia by Masse andFenerci-Masse (2010). The revision of the material collected insouthern Spain (El Caroch) and figured by the latter authors, showsthat the surface of the LV was bored and micritized, precludingthe observation of any ornamentation. Actually specimens from

Bulgaria clearly document the presence of ribs at the surface of theLV, and those of NE Spain as well.

2.5. Patterns of change in size

Because relationships between size and shape have becomeprominent features in evolutionary biology and palaeontology(LaBarbera, 1986; Budd and Johnson, 1991), we analyzed sizepatterns of M. darderi through its long stratigraphic record.

Dimensional data (Table 1) are illustrated by measurements ofthe dorso-ventral (dDV) (116 specimens) and antero-posterior (dAP)(123 specimens) diameters of transverse sections selected on slabsas the largest ones and expected to be as close as possible to thecommissure. Table 1 also illustrates the average diameter obtainedby the addition of two diameters (antero-posterior and dorso-ventral)dividedbytwo(dAverage¼ (dDVþdAP)/2) (111specimens).

The antero-posterior diameter varies from 0.5 to 2.2 cm, itsaverage value being 1.2 cm. The dorso-ventral diameter is slightlyhigher, in the range of 0.6e2.9 cm, its average value being 1.4 cm.The average diameter varies from 0.65 to 2.4 cm (mean 1.3 cm).

The box plot graph (Tukey, 1970) (Fig. 9) represents the meanvalues of the average diameter of specimens belonging to 4stratigraphic intervals: the lowermost Upper Barremian, themiddleUpper and uppermost Barremianelower Aptian, the Upper Aptian(Clansayesian) and the LowereMiddle Albian. The box plotssummarize the following statistical measurements: median, upperand lower quartiles (the box bounds these quartiles), minimumand maximum values.

The box itself accounts for 50% of the data and the line in themiddle indicates the median value.

Table 2 shows that 50% of the average diameters fluctuate from0.7 cm to 0.8 cm for specimens of the lowermost upper Barremian,from 0.75 cm to 1.3 cm for specimens of the middle upper anduppermost Barremian and lower Aptian, from 1 cm to 1.4 cm for

Table 2Stratigraphic variations of the average diameter of Mathesia darderi.

Stratigraphic interval LowermostUpperBarremian

MiddleeUpperand UppermostBarremian

Clansay-esian

LowereMiddleAlbian

Number ofspecimens

11 23 27 50

Mean (cm) 0.76 1.1 1.2 1.6Standard deviation

(cm)0.07 0.4 0.3 0.4

Min (cm) 0.6 0.6 0.7 0.9Max (cm) 0.9 1.9 1.6 2.4

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those of the upper Aptian (Clansayesian), and from 1.25 cm to1.75 cm for those of the early to middle Albian. Notwithstandingmuch overlap, size increases through time. This trend is essentiallymarked by increases both of maximum size, and (albeit lesspronounced) apparent minimum adult size, a pattern whichconforms to Cope’s rule in the strict sense (Jablonski, 1996).

To test the validity of the above stratigraphic grouping wefocused on the average diameters compiled in Table 2. Thesemeasures were compared first by applying the analysis of var-iance (one -way ANOVA method), then followed by the post-hocStudenteNewmaneKeuls test (usually applied for biometric data)using the software STATVIEW with a 0.05 significance level.

Results of the test (Table 3) show that:

1) Specimens of the lowermost Upper Barremian are significantlydifferent from those of the middle upper and Uppermost Bar-remian, Clansayesian, and LowereMiddle Albian;

2) Specimens of the middle Upper and uppermost Barremianand the Clansayesian are similar; measurements of the lowerAptian forms from NE Spain suggest that they fall in the cor-responding group;

3) In contrast specimens from the two foregoing intervals aremarkedly different from those of the LowereMiddle Albian, ata confidence level of 95% (p < 0.0001); and

4) Clansayesian specimens are significantly distinct from those ofthe LowereMiddle Albian.

The biostratigraphic use of M. darderi may be based on thisthreefold pattern for distinguishing the lowermost Upper Barre-mian, uppermost BarremianeClansayesian and Albian p.p.

2.6. Morphological changes through time

Most of the attributes of M. darderi remain identical during thelong range of the species, including the cylindrical habit of the RV,

Table 3Results of the StudenteNewmaneKeuls test applied to Mathesia assemblages ofdistinctive stratigraphic intervals (A, B, C, D): A e lowermost Upper Barremian, B e

middle Upper and uppermost Barremian, C e Clansayesian, D e LowereMiddleAlbian, The “S.” value (significance level) is less than 0.05.

MeanDifference

CriticalDifference

A e lowermost Upper Barremian,B e middle Upper and uppermostBarremian

�0.333 0.202 S

A e lowermost Upper Barremian,C e Clansayesian

�0.472 0.243 S

A e lowermost Upper Barremian,D e LowereMiddle Albian

�0.810 0.267 S

B e middle Upper and uppermost Barremian,C e Clansayesian

�1.39 0.202

B e middle Upper and uppermost Barremian,D e LowereMiddle Albian

�0.477 0.243 S

C e Clansayesian, D e LowereMiddle Albian �0.338 0.202 S

the capuloid, flattened LV, the overall myocardinal traits and theshape of the ventral bands. We discuss the significance of somequalitative changes regarding ornamentation of the RV and tabu-lation of the body cavity, and quantitative changes, mainly size.

2.6.1. Quantitative changesAs shown above, size increase through time is one of the

prominent evolutionary characters ofM. darderi. This phenomenonhas been reported in many rudist lineages, e.g. in the Caprinidae(Skelton, 1994; Skelton and Masse, 1998), Hippuritidae (Steuber,2003) and Radiolitidae (Masse et al., 2007). Plotting the averagediameter calculated for each stratigraphic group versus numericalages show a size increase of 50% from the lowermost Upper Bar-remian to the Middle Albian that is duration in the range of 15 myrwith respect to the Fiet et al. (2006) time scale. We used this timescale instead of that of Gradstein et al. (2004) because it is based onboth isotopic and cyclostratigraphic approaches. Fig. 10 shows thatthe change in size is not linear:, but increased significantly duringthe late Barremian, and between the Clansayesian and the early-middle Albian. During the BedoulianeGargasian, the size remainednearly stable.

2.6.2. Qualitative changesUpper AptianeAlbian representatives of M. darderi, costae are

quite common, but their density is variable and obtuse ribs tendto dominate over acute ones (Mainelli, 1996). Specimens from theupper Barremian of Bulgaria show a pronounced costulationincluding both low obtuse ribs (usually associated with the ventralbands) and numerous intercalated fine and acute costae, from 10 to15 on the anterior side (Fig. 11A). Ribbing is a common adaptivefeature in the tubular Monopleuridae, especially in species orindividuals with a small size and an aggregative behaviour, andfavours anchoring in the substrate or strengthening of shellcongregations, strategies which may apply to M. darderi (Fig. 11B).

The presence of concave upward tabulae in the body cavity of theRV is specific to the Bulgarian specimens (Fig. 11B). A tabulated bodycavity has been considered to be an advanced evolutionary character(e.g. Steuber et al., 2009), and is a common feature in someMiddle toLate Cretaceous rudists. This feature is observed in different families(Caprinidae, Hippuritidae, Radiolitidae, Plagioptychidae), but isuncommon in pre-Albian forms. Pre-Albian tabulate forms includethe early Aptian Offneria murgensis Masse and O. italica Masse, twoadvanced species of the genusOffneria (Masse,1992), though tabulaehave also been observed in some Barremian cylindrical Mono-pleuridae (personal observations of JPM). In the foregoing Barre-mianeearly Aptian forms tabulae are not present in all specimens

Fig. 10. Graph showing the non-linear mode of size increase through time (numericalages based on Fiet et al., 2006, time scale) of Mathesia darderi.

Fig. 11. Transverse sections (RV) of Mathesia darderi from the late Barremian (Fore-Balkan, Bulgaria). A-acute ribs are well developed on the anterior side. B-dense aggregation ofindividuals, some with thin tabulae present in the body cavity (arrow).

M. Fenerci-Masse et al. / Cretaceous Research 32 (2011) 407e421416

and/or all rudist-bearing localities, which means that this characterwas not already fixed in the species in question. In BarremianMathesia the presence of tabulae is also variable and cannot be usedas a firm taxonomic character. The significance of this character isnot clear but may be controlled by some environmental parameters.In summary, qualitative changes observed in M. darderi appearunlikely to have any evolutionary significance and merely reflectlocal ecological conditions.

3. Biogeographical changes through time

Specimens of M. darderi found in Bulgaria and SE Spainrepresent hitherto the oldest occurrences of this species (Fig. 12A).

Fig. 12. Palaeobiogeographic distribution ofMathesia darderi in the Mediterranean Tethys. A-restricted to the European margin. B-during the ClansayesianeAlbian p.p. the species sprea

Extensive field surveys of lower Aptian rudist e bearing carbon-ates of the Mediterranean region, and data from the literature didnot reveal the presence of this taxon (Masse, 1984, 1985, 1996;Luperto-Sinni and Masse, 1992; Masse et al., 1998a, b, 2004;Baron-Szabo and Steuber, 1996; Steuber, 1999; Skelton andMasse, 2000, and personal observations of one of us, JPM), butM. darderi is present in the late Bedoulian of NE Spain. Themigration of the species into the overall Mediterranean region,including the European and AraboeAfrican margins (Fig. 12B),postdates the Mid-Aptian extinction event (Masse and Philip,1986; Masse, 1989; Skelton, 2003) and is associated with thespreading, in the same area, of the family Radiolitidae (Masse andGallo-Maresca, 1997).

during the late BarremianeBedoulian the species has a limited geographic extent and isds over the entire Mediterranean area (modified from Masse et al., 2000).

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Late AptianeAlbian representatives of M. darderi have beenidentified from Spain (Catalonia, Prebetics), Italy, Tunisia, Algeria,France (Ariège), Turkey and Egypt (Fig. 12B). New data on theOuenza limestones from Algeria, show that the single Gargasianlocality documented so far (Masse and Thieuloy, 1979; Chikhi-Aouimeur, 1980; Masse and Chikhi-Aouimeur, 1982) has to beconsidered Clansayesian (personal communication of J.L. Latil).Because late Albian records of M. darderi are missing we canconclude that the disappearance of the species was close to theMiddleeLate Albian boundary.

The foregoing data show that M. darderi is locally and/orpunctually present in the late Barremianelower Aptian and hasa wide record in the Clansayesianeearly to Middle Albian. Thevariations in space and time of this species via the expansion ofits distributional domain, is comparable to the behaviour of manyMediterranean early Cretaceous rudists with time-contrastingbiogeographies, the dynamics of which was mainly controlled byclimatic changes (Masse and Fenerci-Masse, 2008).

4. Ecological changes through time

Data from SE Spain and Bulgaria show that Late BarremianMathesiawas thriving in relatively open marine settings of shallowcarbonate platforms. The section in Rusalya quarry in Bulgaria(Fig. 13) illustrates the environmental context of late BarremianMathesia assemblages. This section consists of five lithologicalunits.

(1) The lower part is composed of bioclastic limestone withboundstone patches composed of small coral colonies andcoral fragments, chaetetids, stromatoporoids, LithocodiumaggregatumeBacinella irregularis consortium, and subordinatelymicrobial crusts (ca. 10 m thick);

(2) Rudist limestone with bioclastic alternations (ca. 15 m);(3) Bioclastic limestone with chaetetids, stromatoporoids, subor-

dinately rudists and small corals (ca. 8 m thick);

Fig. 13. Stratigraphic section of the late Barremian succession of Rusalya quarry (Bulgaria)Chapter 4).

(4) Biostromes composed of dense assemblages of M. darderi andlarge, taxonomically diversified large, branching corals of thesuborder Pachythecaliina, rarely others. M. darderi and coralsappear to occur mostly as separate patches, but they alsooccur closely associated (ca. 2 m thick); and

(5) Limestone composed of large rudists and subordinately chae-tetids (ca. 6 m thick). The access to the topmost part of thesection is difficult, therefore lateral and vertical changes inrudists and corals distribution require further studies.

In Bulgaria dense assemblages of Mathesia are adjacent toPachythecaliina-dominated coral biotopes corresponding to theouter platform zone that is in the distal portion of the rudist-dominated part of the platform (Kolodziej et al., 2009). Biostromeswith M. darderi and branching corals (commonly in growth posi-tion) are associated with dense microbial crusts. Lithocodium/Bacinella encrustations are very rare, in contrast to the lower partof the Rusalya section, which represents a more open platform.Rudists, Pachythecaliina and other large branching corals areabsent there. A unique set of environmental factors permittedflourishing growth of small rudists and pachythecaliine corals,a biotic assemblagewhich is a unique to the Emen Formation of thisarea, and not known from others formations of the Lovech Urgo-nian Group.

In SE Spain Barremian Mathesia tend also to form relativelydense monospecific assemblages on top of requieniid-dominatedbeds and underlying a drowning surface; this stratigraphic positionsuggests that the Mathesia community was more distal thanthe requieniid one.

By contrast, in the late AptianeAlbian the Mathesia communityis associated with platform interiors where it belongs to the groupof innermost rudist populations (Fenerci-Masse, 2006). This envi-ronmental context is illustrated by stratigraphic sections from theAlbian of Turkey and Spain (Fig. 14).

At Barbaros (Karaburun peninsula, Turkey) (Masse et al., inpress) the stratigraphic succession consists of parasequence setsincluding 1e3 m-thick packstones or wackestones with gastropods

showing environmental context of Mathesia-bearing limestones (for explanation see

Fig. 14. Stratigraphic sections of Mathesia-bearing beds of Albian age to illustrate theirsedimentological context. A-Sierra del Carche (SE Spain). B-Barbaros (Karaburunpeninsula, Turkey).

Fig. 15. Temporal ecological changes of Mathesia darderi. From the late Barremian to the Albof the rudist-bearing carbonate platforms; the corresponding ecological replacement is coevafrom Fenerci-Masse, 2006).

M. Fenerci-Masse et al. / Cretaceous Research 32 (2011) 407e421418

and bacinellid oncoids, usually capped by an exposure surfaceand followed by decimetre-thick nodular muddy limestones.Macroscopic evidence of exposure consists of irregular perforatedsurfaces with black pebbles, locally encrusted by oysters, andmicroscopically of the early dissolution of inner rudist shells orgastropod shells, formerly made of aragonite. Rudist-free andrudist-rich beds are interpreted as very shallow settings whereasevidence for inter-or supra-tidal conditions is absent. Rudists areessentially present in relatively thick beds and are representedby two main types of associations: a M. darderi association, thedominant one, and a subordinate Eoradiolites aff. murgensis asso-ciation. M. darderi is usually represented by monospecific denseassemblages forming relatively thick (up to 3 m) bodies. Similardense congregations with a relatively high packing density andcoverage are commonly observed, for example in Tunisia (Tlatli,1980) and Italy (Cestari and Sartorio, 1995). Data from southernSpain (Fenerci-Masse, 2006) document the same trend to builddense monospecific assemblages interbedded with intertidal stro-matolitic laminites and muddy sediments (Fig. 14B).

The ecological changes recorded in Mathesia, from the lateBarremian to the Middle Albian, may be regarded as a lateraltransfer of the corresponding community from distal to proximalsettings of the platform carbonate system (Fig. 15). The foregoingsuggests the origination of Mathesia in distal settings of the rudist-dominated domain of the platform. Rudist communities located inthe distal zone recorded a strong taxonomic turnover first duringthe Bedoulian with the outbreak of the Caprinidae, then duringthe late AptianeAlbian p.p., in correspondence with the diversifi-cation of the Radiolitidae, the outbreak of the Polyconitidae, andthe collapse of the Caprinidae (Fenerci-Masse, 2006). We suggestthat, during the late AptianeAlbian, large, thick-shelled forms, e.g.HoriopleuraeEoradiolites, were well adapted to distal settings andacted as efficient competitors for small size, relatively thin-shelledMathesia which were pushed in low diversity, less competitive,more proximal settings. This process, which involves an ecologicaldisplacement in the sense of Benton (1987), implies a significantecological plasticity and/or a change in ecological needs andtolerance of the species which migrated from open marine to morerestricted environments. The overall history of the Requieniidaealso fits with a similar ecological displacement from distal toproximal settings. The first representative of the family in theKimmeridgian, Hypelasma, was thriving with corals in an open

ian p.p., Mathesia communities were displaced from distal settings to proximal settingsl with a strong turnover of rudist communities thriving in open marine areas (modified

M. Fenerci-Masse et al. / Cretaceous Research 32 (2011) 407e421 419

platform environment (Gourrat et al., 2003), whereas it’s Creta-ceous descendents tended to occupy more proximal settings(Fenerci-Masse, 2006).

5. Origination, development and demise of M. darderi

Data from Bulgaria and SE Spain suggest that the species mayhave originated in the Mediterranean northern margin, includingboth the eastern and western European sub-provinces as definedby Masse (1985). As stated by Masse and Fenerci-Masse (2010)Debrunia, a BarremianeAptian species, and Mathesia have verysimilar morphologies and myophoral organisation, which suggestthat the former derived from the latter. Mathesia appears to bea “Debrunia” with a peculiar microstructure of the inner margin ofthe outer shell layer. The presence of M. darderi in the late Barre-mian shows that the derivation of Mathesia from Debrunia, origi-nally assumed to be located near the early-late Aptian boundary byMasse and Fenerci-Masse (2010) is probably as old as Barremian.

The presence of M. darderi, formerly known only from lateAptianeAlbian, in the late Barremian of Bulgaria and SE Spain,shows that the longevity of this species is in the range of 15 myr.This range is remarkably long if compared with those of the maj-ority of contemporaneous rudist species, the average longevity ofwhich is in the range of 10 myr (most of the BarremianeearlyAptian Requieniidae and Monopleuridae) and far less (4e6 myr)for the early Aptian Caprinidae and some representatives of thelate Aptian Radiolitidae. These values are somewhat comparableto those estimated for Cenozoic bivalves (7 myr) (Stanley, 1977)whereas for some stratigraphic intervals, e.g. Cenomanian, speciesduration is relatively short and in the range of 2 myr (Koch, 1980).

M. darderi escaped the Mid-Aptian crisis during which morethan 90% of the Mediterranean rudist species became extinct, incorrespondence with the disappearance of 70% of the genera,mainly due to the near extinction of the family Caprinidae and thedrastic reduction of representatives of the Requieniidae and theMonopleuridae (Masse, 1989). Large size, aragonite-dominatedforms were selectively extinct during this crisis, as well as mono-specific and some endemic taxa. Notwithstanding its monospecificcharacter, which may have been potentially detrimental forsurviving the crisis, M. darderi possessed many of the survivorshipattributes for being protected from extinction, including its smallsize and calcite-dominated shell, as well as its relatively widegeographic distribution which tends to promote, usually, a higherresistance to elimination (Jablonski, 2004).

Regarding the geographical and stratigraphical extent ofM. darderi, we notice that in wide parts of North Africa most of theEarly Aptian carbonate platforms where rudists were thrivingtended to be drowned near the ClansayesianeAlbian boundary(Masse and Thieuloy, 1979; Tlatli, 1980) precluding the presence ofMathesia during the Albian. This is not the case in Egypt (Steuberand Bachmann, 2002) and Western Turkey (Masse et al., 2010)where Albian carbonates platforms, withM. darderi, were found. InSpain where Albian rudists are well documented (Masse et al.,1998a) the late Albian is marked by an increasing terrigenousinfluence leading to the extreme reduction or disappearance ofrudist-bearing carbonate platforms (Arias et al., 1989). Carbonateplatforms tended also to disappear in southern France during thelate Albian in connection with the development of the Pyreneanrift (Arnaud-Vanneau et al., 1979). In Egypt the MiddleeUpperAlbian transition is marked by the dominance of terrigenous clas-tics detrimental to rudists (Steuber and Bachmann, 2002) while inWesternTurkey the AlbianeCenomanian transition is characterizedby a deepening trend (Masse et al., 2010). Events observed inshallow settings are coeval with significant oceanographic changes

in correspondence with the so-called Oceanic Anoxic Event 1c(Breistroffer event) (Luciani et al., 2004).

The foregoing shows that from the AptianeAlbian transitionand throughout the main part of the Albian suitable habitats forrudists deteriorated, with a peak at the MiddleeLate Albiantransition, notwithstanding a late Albian restoration of shallowwater carbonate platforms, in particular in Spain and Egypt. Thecorresponding pattern documents a spatial reduction and frag-mentation of habitats, known to promote biological extinctions(Bascompte and Solé, 1996). The demise of M. darderi is thereforeinterpreted as the result of environmental modifications affectingshallow carbonate platforms via: deepening or pollution by coastalclastics, causing a limitation and fragmentation of suitablebiotopes. Groups, such as the Polyconitidae and the Radiolitidae,with a possible higher tolerance to ecological perturbations,a higher specific diversity and a wider geographic distribution,survived.

6. Conclusions

M. darderi formerly documented from the late AptianeAlbianhas been discovered in the late Barremianelower Aptian of Bulgariaand Spain. This species is therefore a long-range taxon (in the rangeof 15 myr), if compared with the majority of the contemporaneousrudist species. Notwithstanding some morphological changes (ribs,body cavity tabulae), with a possible environmental significance,forms of the late Barremianeearly Aptian and those of the lateAptianeAlbian are similar, especially regarding their myocardinaland microstructural attributes. The inner shell margin of the leftvalve shows a characteristic assemblage of: scalloped, festooned,tubular and vermiform microstructures, the distribution of whichvaries in the shell of a given individual. Microstructural variabilitytends to decrease with decreasing stratigraphic age. The mostprominent evolutionary trait of M. darderi is body size whichincreases through time (50% increase of the maximum averageshell diameter of the right valve). A statistical approach to sizeanalysis shows that populations of the lowermost Upper Barre-mian, uppermost Barremian to Upper Aptian, and Lower to MiddleAlbian, are significantly different, therefore this threefold distri-bution has a biostratigraphic potential. Ecological changes throughtime are expressed by a displacement of communities from thedistal, rudist-bearing, part (locally with corals) to the proximal partof carbonate platforms. The derivation of Mathesia from Debruniais a Barremian event and the former genus has its first occurrenceon the European Tethyan margin. M. darderi is locally or punctuallypresent in the late Barremianeearly Aptian and is widespread inthe Clansayesianeearly to Middle Albian in correspondence witha major spreading over the European and AraboeAfrican marginsof the Mediterranean Tethys. The disappearance of the species atthe MiddleeUpper Albian boundary correlates with a spatialreduction of suitable habitats, i.e. carbonate platforms tend todeteriorate.

Acknowledgments

We are grateful to C.Arias and L. Vilas (Instituto de GeologíaEconómica-CSIC-UCM, Madrid, Spain), J.M. Castro, G. de Gea and P.A.Ruiz-Ortiz (Universidad de Jaén, Spain) for providing specimensfrom the Sierra de la Muela and their stratigraphic context. Thefinancial support of this study in Spain was involved in the projectCGL2005-C02-02/BTE, from theMinisterio de Educación (Spain). Theproject 2P04D 028 29 (Polish Ministry of Science and HigherEducation), and project 284/09 (University of Sofia, Bulgaria)contributed to the investigations in Bulgaria. We thank R.W. Scottand P.W. Skelton for their helpful review of the original version of the

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manuscript. In additionwe are most grateful to P.W. Skelton and the“Barcelona team” from providing Mathesia specimens from theMaestrat region and their stratigraphic context.

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