4 research outputs found
New ctenodactyloid rodents from the Erlian Basin, Nei Mongol, China, and the phylogenetic relationships of Eocene Asian ctenodactyloids. (American Museum novitates, no. 3828)
58 pages : illustrations ; 26 cm.During the last decade, numerous ctenodactyloid rodent fossils have been systematically collected from at least six horizons of the strata that are distributed from the upper part of the Nomogen Formation to the lower part of the Irdin Manha Formation in the Huheboerhe-Nuhetingboerhe area of the Erlian Basin, Nei Mongol (Inner Mongolia). The ages of these fossiliferous horizons range from the Earliest Eocene to the Middle Eocene. These fossils represent the best-known ctenodactyloid assemblages with a high species diversity and reliable stratigraphic and chronological constraints from one locality in central Asia. The fossils show a relatively continuous record of ctenodactyloids and the earliest radiation of rodents in central Asia beginning from the earliest Eocene. These data are important for biostratigraphic correlation of the Paleogene in central Asia and for understanding the taxonomy of Asian ctenodactyloids and the earliest diversity and evolution of rodents. Among the new fossils, we recognized 10 species that belong to six genera and three morphotypes. Of these taxa, three new genera and species, Chenomys orientalis, gen. et sp. nov., Simplicimys bellus, gen. et sp. nov., and Yongshengomys extensus, gen. et sp. nov., are described. In addition, three new species of Tamquammys, T. robustus, sp. nov., T. longus, sp. nov., and T. fractus, sp. nov., and one new species of Yuomys, Y. huheboerhensis, sp. nov., are also named. With these new materials, we are able to briefly review some existing problems in the taxonomy of early ctenodactyloids, which has remained a difficult task in the study of this Asian rodent group. In light of the new material and taxonomic review, we conducted phylogenetic analyses of ctenodactyloids using a data matrix that contains 38 taxa and 81 characters. Our analysis shows that Chenomys, Tamquammys, and Simplicimys are placed at the base of the clade that contains the extant Ctenodactylus. Yongshengomys is the only taxon that is deeply placed within the clade containing the extant Ctenodactylus and clustered with Chuankueimys and Tsinlingomys. Our analysis supports Gobiomyidae and Ctenodactylidae as monophyletic groups, respectively, but shows that other families and subfamilies traditionally recognized, such as Cocomyinae, Advenimurinae, Tamquammyidae, Yuomyidae, and Chapattimyidae, are probably paraphyletic
New Ctenodactyloid Rodents from the Erlian Basin, Nei Mongol, China, and the Phylogenetic Relationships of Eocene Asian Ctenodactyloids
Early Eocene lagomorph (Mammalia) from Western India and the early diversification of Lagomorpha
We report the oldest known record of Lagomorpha, based on distinctive, small ankle bones (calcaneus and talus) from Early Eocene deposits (Middle Ypresian equivalent, ca 53 Myr ago) of Gujarat, west-central India. The fossils predate the oldest previously known crown lagomorphs by several million years and extend the record of lagomorphs on the Indian subcontinent by 35 Myr. The bones show a mosaic of derived cursorial adaptations found in gracile Leporidae (rabbits and hares) and primitive traits characteristic of extant Ochotonidae (pikas) and more robust leporids. Together with gracile and robust calcanei from the Middle Eocene of Shanghuang, China, also reported here, the Indian fossils suggest that diversification within crown Lagomorpha and possibly divergence of the family Leporidae were already underway in the Early Eocene