Evolution, systematics and functional anatomy of Cricetodontini (Cricetidae, Rodentia, Mammalia) from the northern Junggar Basin, northwestern China.

摘要

I describe here the virtually complete skeletal remains of a new species of Cricetodon recovered from the northern Junggar Basin of China in 1998. The abundant cranial and postcranial materials reported here were found in the middle Miocene Halamagai Formation at the top of a small hillock at the Tieersihabahe localities. The samples include the skulls and mandibles with complete dentition, partially articulated spinal column and ribs, partial forelimb and hindlimb. They are currently the most complete materials of early extinct cricetids.; The new material is here named Cricetodon orientalis sp. nov., and is characterized by medium size; interorbital region relatively narrow and hourglass-shaped with dorsally raised crests; zygomatic plate broad, notch well inscribed; bony plate of palatine long and wide, extending beyond the end of M3; M1 having a distinctly divided anterocone, the posterior paracone spur, four roots; M2 having a pronounced paracone spur and four roots; m1 having a double metalophulid.; Cladistic analysis suggests that C. orientalis is a transitional form in the genus Cricetodon. It is intermediate between primitive species and advanced species of the clade. Advanced species include two clades: one lineage characterized by a rounded m3 is made up of medium-sized and large European species. The other characterized by a complete ectoloph on M1 and M2 is made up of rather small species, the majority of which were distributed in Asia. The phylogeny appears roughly consistent with the geological sequence; that is, primitive taxa occur earlier than derived ones.; The masticatory pattern of C. orientalis is nearly identical to that of the Recent species Mesocricetus auratus, reflecting adaptations to an omnivorous diet, i.e., seeds, fruit, green vegetation, and meat.; The forelimb of C. orientalis exhibits much specialization toward terrestrial, arboreal, and/or fossorial behavior while the hindlimb displays typical characteristics of terrestrial adaptation. In general, C. orientalis was a terrestrial rodent that could climb or dig, like many ground-dwelling rodents living today.; C. orientalis is represented by the first known skull in the genus Cricetodon, and is similar to Miocene and extant species in having an expanded and concave anterior wing of the zygoma, indicating that the skull of cricetids has not changed substantially since the middle Miocene.; C. orientalis sp. nov. is the first record of the genus ever found in Central Asia and is an immigrant from Southwest Asia. Based on the associated faunal remains and age determination, C. orientalis is considered as early Middle Miocene in age, equivalent to the European Neogene land mammal zone MN6. The new discovery of C. orientalis suggests that the diversification of the genus Cricetodon was accompanied not only by migration westward, but also migration eastward into Central Asia and China.