First Record of an Early Barremian Caprinid Rudist from Japan – Implications for the Palaeobiogeography of the Caprinidae (Bivalvia)

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First record of an Early Barremian caprinid rudist from Japan – implications for the palaeobiogeography of the Caprinidae (Bivalvia)

ARTICLE in PALAEONTOLOGY · JULY 2012 Impact Factor: 2.24 · DOI: 10.1111/j.1475-4983.2012.01156.x

6 AUTHORS, INCLUDING:

Shin-ichi Sano Peter William Skelton Fukui Prefectural Dinosaur Museum The Open University (UK)

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Yasuhiro Iba Hokkaido University

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Available from: Peter William Skelton Retrieved on: 18 October 2015 [Palaeontology, Vol. 55, Part 4, 2012, pp. 843–851]

FIRST RECORD OF AN EARLY BARREMIAN CAPRINID RUDIST FROM JAPAN – IMPLICATIONS FOR THE PALAEOBIOGEOGRAPHY OF THE CAPRINIDAE (BIVALVIA) by SHIN-ICHI SANO1*, PETER W. SKELTON2, MEGUMI WATARAI3, YASUHIRO IBA4, YASUO KONDO5 and YUICHIRO SATO6 1Fukui Prefectural Dinosaur Museum, Katsuyama, Fukui 911-8601, Japan; e-mail: [email protected] 2Department of Earth and Environmental Sciences, The Open University, Milton Keynes MK7 6AA, UK; e-mail: [email protected] 3Meikei High School, Tsukuba, Ibaraki 305-8502, Japan; e-mail: [email protected] 4Hokkaido University of Education, Kushiro, Hokkaido 085-8580, Japan; e-mail: [email protected] 5Faculty of Science, Kochi University, Kochi 780-8520, Japan; e-mail: [email protected] 6Oita Geological Society, Ogata, Bungo-ono, Oita 879-6756, Japan; e-mail: [email protected] *Corresponding author.

Typescript received 23 August 2011; accepted in revised form 5 January 2012

Abstract: Pachytraga Paquier, 1900, the stratigraphically Tethyan Pachytraga. The Japanese Pachytraga? represents the oldest genus of caprinine caprinid rudist, was previously first probable record of this genus outside the Mediterra- known from only two chronospecies from a single lineage, nean ⁄ Middle Eastern Tethyan province, and its early Barre- that is the Hauterivian P. tubiconcha Astre, 1961 and the mian age partly fills the ‘gap’ in its previously known early Aptian P. paradoxa (Pictet and Campiche, 1869). stratigraphical record, although the evolutionary relationship Here, a new species, Pachytraga? tanakahitoshii, is erected of the Japanese form with Mediterranean and Middle East on the basis of isolated left valves recovered from the Osaka Tethyan Pachytraga remains unsolved. However, the discov- and Sanchu areas, south-west Japan. This species has a ery of early Barremian Pachytraga? in Japan indicates that moderate shell size (antero-posterior commissural diameter the evolutionary history of the genus is more complex than c. 30 mm), and its left valve is characterized by at least one previously thought and should thus be discussed in a possibly autapomorphic character (narrow anterior myo- broader palaeogeographical context that must now include phore, inclined inwards), as well as a mosaic of primitive the Pacific. (single longitudinal carina developed on the anterior side) and derived (simple marginal canals in the antero-dorsal Key words: Pachytraga, Caprinidae, Barremian, Osaka, valve margin) characters of Mediterranean and Middle East south-west Japan, palaeobiogeography, new species.

The family Caprinidae d’Orbigny, 1847 constitutes the 1998), the absence of this genus from the known record most notable component of mid-Cretaceous rudist evolu- for most of the Barremian is an enigma, and possible con- tion (the ‘Caprinid Phase’ of Skelton 2003) and is divided trols on its restriction to some unknown refugium have into two subfamilies, viz. the Caprininae d’Orbigny, 1847 been discussed by Masse and Fenerci-Masse (2008). Other and the Caprinuloideinae Damestoy, 1971 (Skelton and species have been assigned to the genus, but hitherto, none Smith 2000; Carter et al. 2011). Pachytraga Paquier, 1900 of these attributions has survived revision (Skelton and is the stratigraphically oldest genus of the former subfam- Masse 1998). In particular, Okubo and Matsushima ily, ﬂourishing in the Mediterranean Tethys and Middle (1959) recorded Pachytraga japonica Okubo in Okubo and East during the Hauterivian and in the north-western part Matsushima, 1959 from the Lower Cretaceous Shimanto of the former region during the early Aptian (Skelton and Group of the Akaishi Mountains in central Honshu, Outer Masse 1998, 2000; Masse and Fenerci-Masse 2008). Zone (Paciﬁc side) of south-west Japan. However, Skelton Because Hauterivian P. tubiconcha Astre, 1961 and early and Masse (1998) restudied the holotype and reassigned it Aptian P. paradoxa (Pictet & Campiche, 1869) have been to the polyconitid genus Praecaprotina Yabe and Nagao, considered as successive chronospecies (Skelton and Masse 1926, which had been previously established on the basis

ª The Palaeontological Association doi: 10.1111/j.1475-4983.2012.01156.x 843 844 PALAEONTOLOGY, VOLUME 55 of material from the Miyako Group in north-east Honshu Island and the Yezo Group in central Hokkaido, both north-east Japan (Yabe and Nagao 1926). In addition, material referred to Pachytraga japonica from the putative Barremian–Aptian Osaka Formation in the Osaka area, eastern Kyushu, south-west Japan (Tanaka 1989; Tanaka et al. 1996) has also been reassigned to Praecaprotina, and consequently, doubt has been cast on the existence of Pachytraga in Japan (Sano et al. 2008). Nevertheless, investigation of a specimen referred to ‘Pachytraga japonica’ by Ichise (2008), from the Kanto Mountains near Tokyo, and newly collected specimens from the Osaka area reveal that these specimens show a close similarity to Pachytraga and represent the first probable record of the genus outside the Mediterranean Tethys and Middle East. Interestingly, reinvestigation of age-diagnostic ammonites previously known from these localities indicates their early Barremian age, falling within the ‘gap’ in the known stratigraphical record of this genus in the Mediterranean ⁄ Mid- dle Eastern Tethyan province (Masse and Fenerci-Masse 2008). FIG. 1. Map showing localities in Japan (Osaka and Sanchu) In this study, the new Japanese Pachytraga? is formally which have yielded Pachytraga? named as P?. tanakahitoshii sp. nov. Putative records of other caprinines from the Pacific are also briefly reviewed from the viewpoint of their similarity with those in the by, 1814) from their ‘Northern Belt of the Osaka Forma- Mediterranean Tethyan province. The discovery of early tion’ and broadly assigned a late Barremian–Albian age to Barremian Pachytraga? in Japan indicates that the evolu- the whole Osaka Formation, based on these ammonites tionary history of Pachytraga and also of caprinine rudists and other fossils. Tanaka et al. (1996) recorded Chelonic- in general is more complicated than previously thought eras sp. and Dufrenoyia aff. justinae (Hill, 1893) from and should be discussed in a broader palaeogeographical their ‘Upper Member of the Osaka Formation’, where the context that must now include the Pacific. Pachytraga? specimen here described was recovered and considered its age to be late Aptian, although Iba and Sano (2007) later mentioned that these ammonites proba- GEOLOGICAL SETTING AND AGE bly indicated an early Aptian age. However, restudy of the ammonites recorded by Yokomizo et al. (1990) and The rudist specimens described here were recovered from newly collected specimens from the Osaka area reveals the two localities: Osaka (eastern Kyushu Island) and Sanchu presence of Macroscaphites? sp., Crioceratites sp., Phyllo- (central Honshu Island; Fig. 1). The precise age of the ru- pachyceras sp. and Shasticrioceras sp. in the Osaka Forma- dist-bearing strata in the Osaka and Sanchu areas is still tion (Fig. 2), suggesting an early Barremian age, in controversial, because of complex geological structures comparison with the Early Cretaceous ammonite fauna of and also the scarcity of well-preserved age-diagnostic fos- south-west Japan (e.g. Obata et al. 1982; Matsukawa and sils. In this study, the geological age of these rudist-bear- Obata 1993; Toshimitsu and Hirano 2000; Matsukawa ing strata is discussed chiefly on the basis of ammonites et al. 2007). Unfortunately, the possible early Aptian collected from areas adjacent to the rudist localities. ammonite specimens reported by Tanaka et al. (1996) A single specimen of Pachytraga? was discovered in a were broken after the preliminary investigation, and these sandstone float from locality OS03 (3259¢N, 13138¢10¢¢E) records cannot now be confirmed. Thus, the age of the of Tanaka (1989) and Tanaka et al. (1996) in the Osaka rudist-bearing part of the Osaka Formation is here con- area, Mie Town (Bungoono City, Oita Prefecture). The sidered as early Barremian, although it could be extended upper part of the Osaka Formation, containing abundant to the early Aptian. However, it should be noted that the fossils of shallow-marine origin, crops out in this area finding of Praecaprotina (= Pachytraga japonica in Tanaka (Tanaka 1989; Yokomizo et al. 1990; Tanaka et al. 1996). et al. 1996) and a relatively advanced caprinuloideine ru- Yokomizo et al. (1990) reported the presence of two dist from the Osaka area (Sano et al. 2008) do suggest a ammonite taxa, Eodouvilleiceras(?) sp. aff. E. horridum younger age (possibly Aptian), while complex geological (Riedel, 1938) and Hamites sp. aff. H. attenuatus (Sower- structures in this area are also suspected. SANO ET AL.: EARLY BARREMIAN CAPRINID RUDIST FROM JAPAN 845

AB C D

FIG. 2. Early Barremian ammonites from the Osaka area, eastern Kyushu Island, south-west Japan. A–B, Crioceratites sp., UMUT MM30940, rubber cast of external mould. A, lateral view, B, ventral view. C, Macroscaphites? sp., UMUT MM30941, rubber cast of external mould. D, Phyllopachyceras sp. UMUT MM30942. Scale bar represents 1 cm.

Three specimens of Pachytraga? were obtained from Institutional abbreviations. KSG, Department of Earth Science, granule conglomerate and sandstone beds of the Tozawa Faculty of Science, Kochi University, Kochi; UMUT, University Formation at localities Tz-03 (368¢14¢¢N, 13839¢4¢¢E) Museum, University of Tokyo, Tokyo, Japan. and Tz-19 (367¢45¢¢N, 13839¢26¢¢E) of Ichise (2008), north of the Jikkoku Pass, in the Sanchu area (Kanto Mountains, central Honshu Island). Ichise (2008) defined SYSTEMATIC PALAEONTOLOGY the Tozawa Formation (Nanmoku Group) in this area, although the same strata have been assigned to the upper Family CAPRINIDAE d’Orbigny, 1847 Hauterivian–Barremian Ishido Formation of the Sanchu Subfamily CAPRININAE d’Orbigny, 1847 Cretaceous in other studies (e.g. Matsukawa 1983; Takei 1985; Matsukawa and Tomishima 2009). Ichise (2008) Genus PACHYTRAGA Paquier, 1900 reported Paracrioceras cf. asiaticum (Matsumoto, 1947) from float at locality Tz-03 and also mentioned the report Type species. Sphaerulites paradoxa Pictet and Campiche, 1869, by Hisada et al. (1992) of Paracrioceras aff. elegans (von from erratic blocks of Urgonian limestone in the ‘Plaine des Koenen, 1902), Shasticrioceras nipponicum Matsumoto, Rocailles’, between Regny and La Roche, Switzerland, by the subsequent designation of Paquier (1905). 1947 and Shastricrioceras(?) sp. from the nearby area of Tz-03, concluding that these ammonites indicated a Bar- remian age, by reference to Matsukawa and Obata (1993). However, Ichise (2008) assumed the age of the Tozawa Pachytraga? tanakahitoshii sp. nov. Formation to be Barremian(?) to Aptian, probably Ap- Figure 3 tian, from the similarity of in situ bivalve fossils to those of the putative Aptian Kesado and Osaka formations in non 1959 Pachytraga japonica Okubo in Okubo and Matsushima, p. 1, figs 1–7. Kyushu in preference to the age given by ammonites non 1989 Pachytraga sp. Tanaka, p. 28, pl. 4, fig. 15. recovered from float. Recent findings of ammonites in the non 1996 Pachytraga japonica Okubo and Matsushima Kesado and Osaka formations suggest, rather, that at least [sic]; Tanaka et al., p. 37, pl. 6, figs 4, 5. some (possibly most) parts of them are, after all, Barremi- non 1999 Pachytraga sp. cf. P. japonica Okubo and Matsu- an in age (Tanaka et al. 2009, and see paragraph on the shima [sic]; Tanaka et al., p. 71, pl. 7, figs 5, 6. Osaka Formation above). Thus, it is not necessary to con- 2008 ‘Pachytraga japonica’ Okubo and Matsushima sider the age of the Tozawa Formation as Aptian by com- [sic]; Ichise, p. 51. parison with the Kesado and Osaka formations, and the age of the Pachytraga?-bearing stratum in the Sanchu area Derivation of name. In honour of Dr. Hitoshi Tanaka, Professor is again taken to be early Barremian in this study, apply- of Kumamoto University, for his contributions to the studies of ing the ammonite age assignment in Matsukawa and Cretaceous bivalves and stratigraphy of south-west Japan for Obata (1993) more strictly. over thirty years. 846 PALAEONTOLOGY, VOLUME 55

Holotype. KSG-ss010 (Fig. 3A–D), internal and partial external antero-dorsal margin of the left valve of the holotype (Fig. 3A– mould of incomplete left valve, collected by H. Tanaka, Y. Iba B). The right valve of this species has not been recovered yet. and S. Sano from the Osaka area (see previous section), eastern Kyushu Island, south-west Japan. Remarks. The new species shares diagnostic characters of cardinal and posterior myophoral arrangement with Other material examined. Three moulds of incomplete left valves; Pachytraga: two unequal teeth with the bluntly conical KSG-ss011-1, both external and internal mould (Fig. 3G–I) from anterior tooth significantly larger than the posterior one; Tz-19; KSG-ss011-2, internal mould (Fig. 3E, F) from the same posterior tooth and erect posterior myophoral ridge con- rock specimen with KSG-ss011-1, and KSG-ss012, internal mould necting dorsally to the posterior tooth both situated on (Fig. 3J, K) from Tz-03, collected and reported by M. Ichise the valve wall; a large endomyophoral cavity adjoining (maiden name of M. Watarai) from the Sanchu area (see previous section), Kanto Mountains, central Japan (Ichise, 2008). the central tooth socket, separated from the body cavity by a thin vertical wall extending from the anterior tooth Diagnosis. Moderate-sized shell (antero-posterior commis- to the postero-ventral valve margin. sural diameter c. 30 mm) with Pachytraga-like cardinal The two already known species of Pachytraga, P. tubi- and, apparently, posterior myophoral arrangement; com- concha and P. paradoxa, generally have similar morpho- missural outline almost oval, somewhat compressed dorso- logical features and have been considered as successive ventrally; left valve domed to conically capuloid, with a chronospecies showing phyletic size increase (Skelton and longitudinal carina developed on the anterior side; anterior Masse 1998). The size of the Japanese Pachytraga? is just myophore of the left valve relatively recessed with only a above the size range of P. tubiconcha shown in Skelton narrow connection to the base of the anterior tooth and and Masse (1998). However, some differences between inclined into the valve interior; small marginal canals may the Japanese form and either, or both, of the two previ- be developed on the antero-dorsal margin of the left valve. ously known species of Pachytraga are evident. Thus, in the Japanese specimens, an external posterior longitudinal Description. The left valve is low-domed in shape and the umbo ridge is not developed as it is in P. tubiconcha. On the little extended (Fig. 3C, D, H, K) with a single longitudinal car- other hand, although small marginal canals in the antero- ina on the anterior side (Fig. 3G, I); the commissural outline dorsal side of the left valve are not known in P. tubicon- may be almost oval in shape, with the maximum diameter-ori- cha, they are in some specimens of P. paradoxa (Skelton ented antero-posteriorly (Fig. 3A, B, G). The two teeth are and Masse 1998, 2000). Yet, left valves of the latter spe- unequal, with the bluntly conical anterior tooth significantly lar- cies, by contrast, usually show a small, but distinct mid- ger than the posterior one in the left valve (Fig. 3B, D, F). A ventral ridge extending down inside the body cavity large endomyophoral cavity adjoins the central tooth socket and (Skelton and Masse 1998), a feature not seen in any of is separated from the body cavity by a thin vertical wall extend- the Japanese specimens. ing from the anterior tooth to the postero-ventral valve margin Moreover, all specimens of the Japanese Pachytraga? (Fig. 3B, D, F, G, J). The erect posterior myophoral ridge is situated on the posterior valve wall and connects dorsally to the have a low-domed left valve and do not show the project- posterior tooth (Fig. 3B, D, F); in none of the specimens, unfor- ing, prosogyrally enrolled umbo often observed in both tunately, is its ventral termination preserved, but the visible P. tubiconcha and P. paradoxa (Fig. 3). Furthermore, the remains suggest a salient ridge fully seated on the posterior valve commissural outline is somewhat compressed dorso-ven- wall (Fig. 3A, B, E, F). The anterior myophore of the left valve trally in the Japanese form, in contrast to those of P. tubi- is relatively recessed along the shell wall with connection only to concha and P. paradoxa, which are slightly compressed the base of the anterior tooth and inclined into the interior of antero-posteriorly. Finally, and perhaps most significantly the valve (Fig. 3B). Small marginal canals are developed on the in terms of taxonomic characterization, the anterior myo-

FIG. 3. Pachytraga? tanakahitoshii sp. nov. from Japan. Abbreviations: at, anterior tooth; am, anterior myophore; pt + pm, conjoined posterior tooth and myophore; cts, central tooth socket; lt, ligamentary trace; bc, body cavity; emc, endomyophoral cavity; w, wall separating endomyophoral cavity from body cavity; c, carina. A–D, KSG-ss010 (holotype), left valve, from the Osaka area. A, Internal and partial (dorsal) external mould. B, Commissural view of plastic cast taken from A. Note the presence of simple canals on antero- dorsal margin of the shell, and relatively narrow am inclined into the valve interior. C, Detail of external mould of the umbonal part. D, Postero-dorsal view of plastic cast showing large at, and pt and part of pm located on the shell margin. E–F, KSG-ss011-2, left valve from the Sanchu area. E, Internal mould. F, commissural view of plastic cast taken from E. Note that some bulges corresponding to shell fragments of other bivalves are also shown. G–I, KSG-ss011-1, left valve from the Sanchu area. G, Internal mould. The well- developed antero-ventral carina is recognizable. H, dorsal view of internal mould. Note relatively lower-domed shape of the valve. I, Exterior of the plastic cast showing external form. Note the development of antero-ventral carina (c). J–K, KSG-ss012, left valve from the Sanchu area. J, Internal mould. K, Dorsal view of internal mould. Note that dorsal tip of the internal mould of myophoral cavity is broken. Scale bar represents 1 cm. SANO ET AL.: EARLY BARREMIAN CAPRINID RUDIST FROM JAPAN 847

C B A

E F

J K 848 PALAEONTOLOGY, VOLUME 55 phore of the left valve in the Japanese form is relatively derived independently of the Mediterranean and Middle narrow and inclined into the valve interior, whereas those East Tethyan Pachytraga lineage, from a more primitive in both P. tubiconcha and P. paradoxa are broader and common ancestral form, despite sharing the relatively flat or even tilted upwards to face out onto the depressed derived character of antero-dorsal canals with P. paradoxa anterior myophore on the anterior wall of the right valve (which, in that case, would thus be homoplasious); or it (Skelton and Masse 1998). Thus, the Japanese Pachytraga? diverged from the latter’s lineage, autapomorphically has a puzzling mosaic of characters of both P. tubiconcha re-assuming a more primitive anterior myophoral form. and P. paradoxa, as well as some possible autapomorphic In the former case, the Japanese form could be placed in characters, so can be distinguished from the two known a separate, more primitive genus, possibly tracing back to species of Pachytraga. the Late Jurassic; in the latter case, the Japanese form Mention should also be made of a single left valve should remain within the genus Pachytraga. This question reported from the lower Aptian of central Greece by cannot be settled without further information, especially Baron-Szabo and Steuber (1996) under the name of on the form of the right valve. Thus, the Japanese form is P. paradoxa. This latter form does have a low-domed tentatively assigned to Pachytraga here. shape with dorso-ventrally compressed commissural outline and shows little umbonal protrusion, similar to Distribution and stratigraphic range. Probably lower Barremian Pachytraga? tanakahitoshii sp. nov. Indeed, Skelton and in the Osaka and Sanchu areas, south-west Japan. Masse (1998, p. 347) already regarded these same characters as casting doubt on the assignment of the Greek specimen to P. paradoxa. However, the larger size and IMPLICATIONS FOR EVOLUTIONARY acute projection of the anterior part of the valve in the HISTORY OF THE GENUS latter, and, particularly, its broad anterior myophoral PACHYTRAGA shelf (like that in P. paradoxa) are distinct from the Japa- nese form. The similarities in external shape may thus be The distribution of Pachytraga has recently been summa- merely convergence. In fact, the taxonomic status of the rized by Masse and Fenerci-Masse (2008). The Hauteri- Greek specimen itself remains problematical, as its rela- vian P. tubiconcha is recorded from south-east France, tively broadly inward-sloping posterior myophore might Switzerland, Sardinia, southern Spain, Portugal, Algeria alternatively suggest kinship with the Himeraelites ⁄ Sellaea and Oman. On the other hand, its early Aptian descen- group (family Caprinulidae Yanin, 1990 in Carter et al. dant, P. paradoxa, is known only from south-east France, 2011) rather than with Pachytraga – a possibility that Spain, Portugal and Algeria. Although Baron-Szabo and remains to be tested by reference to other, as yet unpub- Steuber (1996) noted P. paradoxa also from central lished material from the same locality, including diagnos- Greece, this assignment is questionable, as discussed tically important right valves. above. The absence of Pachytraga from the known record for most of the Barremian in the Mediterranean ⁄ Middle Systematic position. Although Pachytraga? tanakahitoshii Eastern Tethyan province is an enigma (Masse and Fen- sp. nov. shares its cardinal and posterior myophoral erci-Masse 2008). In addition, Skelton and Masse (1998) arrangement with Pachytraga, some of its morphological mentioned possible early Aptian examples (Pachytraga? characters, such as the relatively unextended umbo, sp.) from Cuba in the Caribbean Province. Subsequently, dorso-ventrally compressed commissural outline, and the the rudist limestones at the locality of Tumbadero in narrow and inwardly inclined form of the anterior myo- Cuba were considered more likely to be Barremian, phore of the left valve are not observed in its congeners. because of the presence there of Offneria simplex Chart- Thus, if the Japanese form is eventually assigned to the rousse and Masse, 1998b. The Japanese early Barremian genus Pachytraga, the diagnosis of the latter would need Pachytraga? is, perhaps together with the above-men- to be amended correspondingly. However, we refrain tioned Cuban material, not only the first possible record from doing so at present in view of the limitations of of this genus outside the Mediterranean ⁄ Middle Eastern the material so far available, especially the lack of right Tethyan province, but also partially fills the ‘gap’ in the valves. known stratigraphical record, although the reasons for the The above-mentioned characters of the Japanese Pachy- disappearance and revival of the genus in the Mediterra- traga?, however, can be observed in at least some speci- nean ⁄ Middle Eastern Tethyan province remain unsolved. mens of right valve-attached rudists of Late Jurassic age, Furthermore, as the early Barremian P.? tanakahitoshii such as ‘Valletia’ antiqua Favre in Joukowsky and Favre sp. nov. has a mosaic characters of Hauterivian P. tubicon- (1913) and ‘Valletia’ auris Favre in Favre and Richard cha and early Aptian P. paradoxa, and also some possible (1927; SS and PWS, pers. obs.). Such information leaves autapomorphic characters, it could be an endemic north- open two possibilities: either the Japanese Pachytraga? was west Pacific-margin offshoot from the main Pachytraga SANO ET AL.: EARLY BARREMIAN CAPRINID RUDIST FROM JAPAN 849 lineage or it could even have been derived from an older Shikama and Tanabe (1970) described Caprina uwajim- common ancestor. Either way, the evolutionary history of ensis from the Uwajima area, western Shikoku Island, Pachytraga is probably more complex than previously south-west Japan. Our reinvestigation of the holotype and thought and should be discussed in a broader palaeogeo- newly collected specimens from a nearby locality reveals graphical context that must now include the Pacific and that the putative pallial canals of ‘C. uwajimensis’ are not possibly the Caribbean, at least in the Barremian. located in the inner shell layer, but in the outer shell layer. Thus, it does not belong to the Caprinidae. Tightly pleated infoldings of the outer shell layer indicate its affinity, COMMENTS ON PUTATIVE CAPRININE rather, to certain specialized polyconitids, such as Horiople- RECORDS IN THE PACIFIC ura? juxi Steuber, 1999 from Greece (Steuber et al. 2011). In summary, we can confirm the presence of at least two Two biotic provinces, Mediterranean and Caribbean, probably caprinine species in the Pacific: early Barremian were established in the Tethyan Realm from the early Pachytraga? tanakahitoshii sp. nov. from Japan and late Al- Aptian onwards (Chartrousse and Masse 2004), probably bian Caprina mulleri from the Mid-Pacific Mountains. because of separation due to the formation of the Atlan- Both species show strong affinities with Mediterranean tic (e.g. Coates 1973). As the Caprininae flourished in species, implying the expansion of caprinine distribution both the Mediterranean (largely) and Caribbean prov- to the Pacific at least in early Barremian and late Albian inces, and the Caprinuloideinae mainly in the Caribbean times, although the connecting routes remain unknown. province, caprinid rudists are considered as key palaeo- Two enigmatic bio-events in the evolutionary history of biogeographic indicators (Chartrousse and Masse 2004). the caprinine rudists in the Mediterranean ⁄ Middle Eastern In this context, the presence of caprinuloideine rudists Tethyan province are the absence of Pachytraga for most in the Central Pacific has attracted attention in recent of the Barremian, and of the whole of the subfamily in the palaeobiogeographic studies of the Pacific (e.g. Premoli late Aptian–middle Albian (e.g. Skelton 2000; Masse and Silva et al. 1995; Chartrousse and Masse 1998a; Skelton Fenerci-Masse 2008). The ‘rediscovery’ of caprinine rudists et al. 2011). in the Pacific possibly provides the clue in the search for Putative caprinine rudists, however, have been recorded the refugia of the caprinines during these lacunae in their from the Pacific, though their systematic assignments known stratigraphical record. Further studies of the Pacific have proved controversial. Caprina mulleri and C. medio- and possibly northern Tibet rudist records (e.g. Scott et al. pacifica were described by Hamilton (1956), based on the 2010) are necessary to reveal the missing chapters in the dredged materials from Cape Johnson Guyot in the Mid- evolutionary history of these rudists. Pacific Mountains. Later, Swinburne and Masse (1995) suggested that these species were probably synonymous, Acknowledgements. We acknowledge helpful discussions with but questioned their relationship to Caprina or even the Jean-Pierre Masse (Universite´ de Provence, Marseille) concern- known subfamilies of the Caprinidae, while Chartrousse ing the taxonomy of the rudists discussed herein. We are (1998, pp. 190, 191) proposed reassignment to a new grateful to Hitoshi Tanaka (Kumamoto University) and genus within the ‘Coalcomaninae Coogan, 1973’ (= Capr- Ken-ichiro Hisada (University of Tsukuba) for their kind help in conducting the geological and palaeontological studies of inuloideinae). However, reinvestigation of the holotype of the Osaka Formation and the Sanchu Cretaceous. We would C. mulleri deposited at the Smithonian National Museum like to thank Thomas Steuber (Petroleum Institute, Abu of Natural History (Washington, DC) and additional Dhabi) and an anonymous reviewer for critical comments on Pacific specimens confirms its original generic attribution, an earlier version, and John W. M. Jagt (Natuurhistorisch indeed emphasizing similarities with the coeval late Al- Museum Maastricht) for his editorial work. Thanks are bian C. choffati Douville´, 1898 from Iberia, for example extended to Yasunari Shigeta and Yuta Shiino (National in having opisthogyral umbones (Skelton et al. 2011; Museum of Nature and Science, Tokyo) for their help in PWS and SS, work in progress with J-P Masse). identification and taking the photographs of ammonite speci- Although Swinburne and Masse (1995) reported possi- mens, respectively. ble caprinine rudists of early Aptian age from Resolution Guyot in the Mid-Pacific Mountains, Chartrousse and Editor. John Jagt Masse (1998a) formally described well-preserved rudist specimens including those discussed by Swinburne and Masse (1995) as a new genus and species, Conchemipora REFERENCES skeltoni, which they assigned to the Coalcomaninae ´ (= Caprinuloideinae). Thus, the presence of caprinines in ASTRE, G. 1961. 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