Grégoire Métais

Laonastes and the "Lazarus effect'' in recent mammals

The living Laotian rodent Laonastes aenigmamus, first described in early 2005, has been interpreted as the sole member of the new family Laonastidae on the basis of its distinctive morphology and apparent phylogenetic isolation from other living rodents. Here we show that Laonastes is actually a surviving member of the otherwise extinct rodent family Diatomyidae, known from early Oligocene to late Miocene sites in Pakistan, India, Thailand, China, and Japan. Laonastes is a particularly striking example of the “Lazarus effect” in Recent mammals, whereby a taxon that was formerly thought to be extinct is rediscovered in the extant biota, in this case after a temporal gap of roughly 11 million years.

New remains of primitive ruminants from Thailand: evidence of the early evolution of the Ruminantia in Asia

A new tragulid, Archaeotragulus krabiensis, gen. n. et sp. n., is described from the late Eocene Krabi Basin (south Thailand). It represents the oldest occurrence of the family which was previously unknown prior to the Miocene. Archaeotragulus displays a mixture of primitive and derived characters, together with the M structure on the trigonid, which appears to be the main dental autapomorphy of the family. We also report the occurrence at Krabi of a new Lophiomerycid, Krabimeryx primitivus, gen. n. et sp. n., which displays affinities with Chinese representatives of the family, particularly Lophiomeryx. The familial status of Iberomeryx is discussed and a set of characters is proposed to define both Tragulidae and Lophiomerycidae. Results of phylogenetic analysis show that tragulids are monophyletic and appear nested within the lophiomerycids. The occurrence of Tragulidae and Lophiomerycidae in the upper Eocene of south‐east Asia enhances the hypothesis that ruminants originated in Asia, but it also challenges the taxonomic status of traguloids within the Ruminantia.

First Clarkforkian equivalent Land Mammal Age in the latest Paleocene basal Sparnacian facies of Europe: fauna, flora, paleoenvironment and (bio)stratigraphy.

The Paleocene-Eocene Thermal Maximum (PETM) is correlated with the first occurrences of earliest modern mammals in the Northern Hemisphere. The latest Paleocene Clarkforkian North American Land Mammal Age, that has yielded rodents and carnivorans, is the only exception to this rule. However, until now no pre-PETM localities have yielded modern mammals in Europe or Asia. We report the first Clarkforkian equivalent Land Mammal Age in the latest Paleocene deposits of the basal Sparnacian facies at Rivecourt, in the north-central part of the Paris Basin. The new terrestrial vertebrate and macroflora assemblages are analyzed through a multidisciplinary study including sedimentologic, stratigraphic, isotopic, and palynological aspects in order to reconstruct the paleoenvironment and to evaluate biochronologic and paleogeographic implications. The mammals are moderately diverse and not abundant, contrary to turtles and champsosaurs. The macroflora is exceptional in preservation and diversity with numerous angiosperms represented by flowers, fruits, seeds and wood preserved as lignite material, revealing an abundance of Arecaceae, Betulaceae, Icacinaceae, Menispermaceae, Vitaceae and probably Cornaceae. Results indicate a Late Paleocene age based on carbon isotope data, palynology and vertebrate occurrences such as the choristoderan Champsosaurus, the arctocyonid Arctocyon, and the plesiadapid Plesiadapis tricuspidens. However, several mammal species compare better with the earliest Eocene. Among these, the particular louisinid Teilhardimys musculus, also recorded from the latest Paleocene of the Spanish Pyrenees, suggests a younger age than the typical MP6 reference level. Nevertheless, the most important aspect of the Rivecourt fauna is the presence of dental remains of a rodent and a “miacid” carnivoran, attesting to the presence of two modern mammalian orders in the latest Paleocene of Europe. Interestingly, these two groups are also the only modern groups recorded from the latest Paleocene of North America, making Rivecourt the first direct equivalent to the Clarkforkian Land Mammal Age outside of North America.

New tropical carcharhinids (chondrichthyes, Carcharhiniformes) from the late Eocene-early Oligocene of Balochistan, Pakistan: Paleoenvironmental and paleogeographic implications

New selachians (sharks and rays) have been collected from several late Eocene and early Oligocene marine localities in the Bugti Hills (Balochistan, Pakistan). Two new species of Requiem sharks (close to the Recent ?Bull shark?) are described : Carcharhinus balochensis and Carcharhinus perseus. The rest of the fauna is notable for the strong representation of Carcharhiniformes. These selachian faunas represent a unique tropical association for the Oligocene period and one of the first modern tropical selachian faunas, with modern taxa such as the two new species of ?Bull sharks?, Negaprion sp. and one of the first occurrences of Sphyrna sp. Moreover, these faunas permit paleoenvironmental interpretation of adjacent land masses. The relatively modern aspect of these faunas, compared with other contemporaneous and younger selachian associations from Atlantic and Mediterranean seas, suggests biogeographic isolation of selachian communities living in eastern and western parts of the Tethys before its final closure during the early-middle Miocene.

Eocene bunoselenodont Artiodactyla from southern Thailand and the early evolution of Ruminantia in South Asia

Although Asia is thought to have played a critical role in the basal radiation of Ruminantia, the fossil record of early selenodont artiodactyls remains poorly documented in this region. Dental remains of a new bunoselenodont artiodactyl are described from the late Eocene of Krabi, southern Thailand. This new form, Krabitherium waileki gen. et sp. nov, is tentatively referred to the Tragulidae (Ruminantia) on the basis of several dental features, including a weak Tragulus fold and the presence of a deep groove on the anterior face of the entoconid. Although this new form is suggestive of the enigmatic ?Gelocus gajensis Pilgrim 1912 from the “base of the Gaj” (lower Chitarwata Formation) of the Bugti Hills (Central Pakistan), K. waileki most likely represents an early representative of a relatively bunodont group of tragulids that includes the genus Dorcabune, known from the Miocene of south Asia. This addition to the Eocene record of early ruminants attests to the antiquity of the group in Southeast Asia and lends support to the hypothesis that the Tragulidae represents one of the first offshoots in the evolutionary history of Ruminantia.

Mosaicomeryx gen. nov., a ruminant mammal from the Oligocene of Europe and the significance of ‘gelocids’

The description of new material and the reassessment of specimens previously assigned to Gelocus quercyi lead us to propose a new genus for this species, Mosaicomeryx gen. nov. Moreover, the description of a juvenile skull and other specimens of Prodremotherium elongatum, and comparison with Dremotherium, provide evidence that these two genera are not closely related as previously thought. A phylogenetic analysis based on 40 dental, cranial and postcranial features highlights the misidentification of Gelocus quercyi and suggests that Mosaicomeryx gen. nov. is closely related to Prodremotherium elongatum. Mosaicomeryx quercyi and Prodremotherium elongatum form a monophyletic group of stem Pecora that first appeared in Western Europe by the late Early Oligocene (MP25–26), and Prodremotherium elongatum persisted up to MP28; following this time both taxa appear to be replaced by Dremotherium and Amphitragulus. This time interval covers two major Oligocene faunal and climate changes: Extinction 1 (MP24), associated with regression of the inner European sea, and Extinction 3/Migrations 3 (MP28), associated with Late Oligocene Warming. http://zoobank.org/urn:lsid:zoobank.org:pub:CC044612-B707-4CCD-B121-0830DA304396

Middle-Eocene artiodactyls from Shanghuang (Jiangsu Province, Coastal China) and the diversity of basal dichobunoids in Asia.

A new assemblage of basal dichobunoid artiodactyls from the middle-Eocene Shanghuang fissure fillings includes the diacodexeid Jiangsudon shanghuangensis gen. and sp. nov., a new species of the lantianine dichobunoid Elaschitotherium, Elaschitotherium crepaturus sp. nov., and an indeterminate suoid which is presently the earliest record of this clade. Diacodexeids are also represented by two forms provisionally referred to cf. Diacodexis sp. and to an indeterminate Diacodexeidae, respectively. The occurrence of diacodexeids in Shanghuang contrasts with the early and earliest middle-Eocene chronological range of the family in Europe and North America and suggests that the stratigraphic range of the family in Asia extends up to the middle Eocene. This may reflect particular habitats in coastal China that may have been relatively stable during the early and middle Eocene, thus preserving forest-dwelling artiodactyls that became extinct in the other Holarctic regions. Compared to other supposedly coeval North American, European, and Asian faunas, the Shanghuang mammalian assemblage is most similar to early Uintan faunas of North America but is also remarkable in recording forms close to taxa that are characteristic of the Wasatchian and Bridgerian North American Land Mammal Ages. The Irdinmanhan age of the Shanghuang fauna is supported by the mammalian assemblage recovered from the fissure D, but an Arshantan age cannot be completely ruled out at this point. Although the Shanghuang assemblage is biased towards preservation of small components of the mammalian fauna, the Shanghuang fauna provide an important and unique window into the Eocene diversity and early evolution of cetartiodactyls in eastern Asia.

Re-interpretation of the genus Parabunodon (Ypresian, Turkey): implications for the evolution and distribution of pleuraspidotheriid mammals

Early Paleogene mammal faunas from western Asia remain very poorly documented, and the few fossil data currently available raise more issues than they provide answers regarding the palaeobiogeography of the Peri-Tethys area during a key period for the diversification and dispersal of modern group of mammals. Parabunodon anatolicum is an ungulate mammal whose both age and taxonomic affinities are disputable. The holotype of this monotypic genus was collected from the early? Eocene Çeltek Formation, Central Anatolia, Amasya Province, and described as a choeropotamid artiodactyl, making it the easternmost occurrence of the family which is mostly restricted to the middle–late Eocene of western Europe. Here, we revisit the relationships of Parabunodon anatolicum in the light of recent studies. The reassessment of dental features of this genus as well as of its phylogenetic relationships led us to reconsider the taxonomic assignment of this still enigmatic form. Cladistic analysis was undertaken to understand its relationships with the Pleuraspidotheriidae and the Choeropotamidae, in which Parabunodon had earlier been included. Our analysis supports the relationships of Parabunodon with other pleuraspidotheriids. It implies an early diversification and a vast geographic distribution from western Europe to Anatolia of pleuraspidotheriid ‘condylarths’ during the early Paleogene.

Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography

The paleobiodiversity of the Volutidae (Mollusca: Gastropoda) of the Ranikot Group (Sindh, Pakistan) and particularly of the Lakhra Formation (SBZ 5 biozone, Earliest Eocene), is reconsidered on the basis of new material collected during recent field trips. Ten new species are described (Mitreola brohii sp. nov., Lyrischapa vredenburgi sp. nov., L. brevispira sp. nov., Athleta (Volutopupa) citharopsis sp. nov., A. (Volutocorbis) lasharii sp. nov., Volutilithes welcommei sp. nov., V. sindhiensis sp. nov., Pseudaulicina coxi sp. nov., Sindhiluta lakhraensis sp. nov. and Pakiluta solangii sp. nov.) and one species is in open nomenclature (Lyria sp.). Three new genera are described: Lyriopsis gen. nov. [Volutinae, ?Lyriini, type species: Lyriopsis cossmanni (Vredenburg, 1923)], Sindhiluta gen. nov. [Volutilithinae, type species: Sindhiluta lakhraensis n. sp.] and Pakiluta gen. nov. [?Volutodermatinae, type species: Pakiluta solangii n. sp.]. Two new combinations are proposed: Lyriopsis cossmanni (Vredenburg, 1923) comb. nov. and Athleta (Volutopupa) intercrenatus (Cossmann & Pissarro, 1909) comb. nov. Lectotypes are designated for Lyria cossmanni Vredenburg, 1923, L. feddeni Vredenburg, 1923, Volutospina noetlingi Cossmann & Pissarro, 1909, V. intercrenata Cossmann & Pissarro, 1909 and Athleta (Volutocorbis) victoriae Vredenburg, 1923. With 21 species, this volutid fauna is the most diverse recorded from the Tethys Ocean during Earliest Eocene time. The assemblage is characterized by a strong turnover marked by regional speciation and the appearance of many western Tethyan invaders. Although at the species level, the assemblage documents a strong provincialism, at the genus level, the high number of shared genera between Eastern Tethyan and Old World Tethyan realms begins a phase of long-term homogeneity of volutid assemblages from the Tethyan paleobiogeographic province.

New Lophiomerycid Ruminants from the Oligocene of the Bugti Hills (Balochistan, Pakistan)

ABSTRACT A new assemblage of ruminants from Paali in the lower Chitarwata Formation, Bugti Hills, Balochistan, central Pakistan, includes two lophiomerycids, Lophiomeryx, and Nalameryx gen. nov., allowing revision of ruminants previously reported from the Oligocene of the Indian Subcontinent. Two species are referred to Nalameryx: N. savagei (formerly Iberomeryx savagei), and N. sulaimani nov. sp. The middle Oligocene age previously assigned to the lower unit of the Chitarwata Formation in the Bugti area, mostly based on the rodent fauna from Paali, is supported by the composition of the ruminant fauna, which consists of taxa exclusively known in the Oligocene of Eurasia. The new ruminant fauna from Paali is clearly distinct from the early Miocene assemblages known in the Bugti hills, and suggests the existence of densely forested habitat probably mixed with more open areas in central Pakistan during the middle Oligocene.