Paleogene mammal localities are particularly well represented in the area of Erlianhot, Inner Mongolia. Among them, the locality of Bayan Ulan is most famous for its late Paleocene Gashatan fauna. The Arshantan fauna of the site is not well known, since no extensive study has been done so far. Here we present a mammal assemblage based on dental and tarsal material from a new Arshantan collection resulting from excavations done by a Belgian-Chinese expedition in Inner Mongolia in 1995 – retrieved from the red beds of the late early to early middle Eocene Arshanto Formation at Bayan Ulan. It consists of at least six different taxa: the primitive lagomorph Dawsonolagus antiquus, the large pantodont Pantolambdodon sp., the lophialetid tapiroid Schlosseria magister, the rhinocerotoid Hyrachyus crista, and a new smaller rhinocerotoid. The latter is closely related to the genera Yimengia and Rhodopagus. The species exhibits transverse Hunter-Schreger bands, no reduction of the lower premolars, m3 has no hypoconulid, and P4 bears a continuous “V”-shaped protolophmetaloph loop. The Arshantan assemblage at Bayan Ulan is dominated by small perissodactyls, represented by extensive lower and upper dentition as well as foot bones. Also, for the first time, p4-m1 of Dawsonolagus antiquus, tarsal material from Pantolambdodon, and lower dentition of Hyrachyus crista are illustrated. Unlike other described Arshantan faunas, the Bayan Ulan Arshantan mammal assemblage has been collected exclusively from a single locality, which allows it to be used in the reassessment of the Arshantan Land Mammal Age. This research has been funded by project MO/36/011 and bilateral cooperation project BL/36/C12 of the Belgian Federal Science Policy Office.
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RBINS Staff Publications 2019
The early Eocene Cambay Shale Formation in Gujarat State, India has produced a rich mammalian fauna, including the earliest artiodactyls, perissodactyls, primates, hyaenodonts, rodents, lagomorphs, chiropterans, and tillodonts from the Indian Subcontinent. While some of these groups show endemism at the generic or familial level, all belong to clades that are widely distributed across Laurasian continents, and some show particularly close similarities to contemporary taxa from other continents, particularly Europe. We report here a distinctive new taxon, represented by a mandible with p3-m3 and a second mandibular fragment with m3. The morphology of the new taxon is broadly comparable to diverse early ungulates from around the world but shows a unique suite of features including a strongly fused mandibular symphysis, enlarged anterior tooth alveolus, simple premolars lacking paraconids and with only a rudimentary metaconid on p4, progressive size increase of the molars distally, molar exodaenodonty/unilateral hypsodonty, molar paraconids absent, hypoconulids absent on m1-2, incipient development of selenodont buccal cusps and an incipient entolophid formed by a transverse entoconid, well-developed, and prominent m3 hypoconulid. One particularly distinctive feature is the presence of large, cuspate ectostylids on molar hypoflexids. While there are similarities to a variety of taxa, most notably periptychids, louisinids, early African “ungulates” (Abdounodus, Ocepeia), and even early anthracotheres, none of these is detailed enough to indicate a close relationship, and all appear to be better interpreted as convergence. Our present understanding suggests that these fossils represent a new family of “condylarth”-grade ungulates perhaps endemic to India. Although their overall adaptations are very different, there are some intriguing similarities to another group of enigmatic Eocene mammals from the Indian Subcontinent, Quettacyonidae. While more material is needed to test this possible relationship, quettacyonids and the new taxon may represent remnants of the eutherian fauna present in India prior to its first faunal exchange with the northern continents, and the new taxon likely has a lengthy, undocumented history in the Indian Paleocene. Grant Information: Fieldwork and research supported by Leakey Foundation, National Geographic Society, Wadia Institute of Himalayan Geology, and Belgian Science Policy Office.
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RBINS Staff Publications 2017
