Discovery Of Sinolagomys (Lagomorpha,Ochotoninae) Skulls From Late Oligocene Strata Of Saint-Jacques,Inner Mongolia

Ochotonidae is a group of small-sized lagomorphs,and forms the order Lagomorpha together with Leporidae.The possible earliest fossils of Ochotonidae is Desmatolagus cf.D.vetustus from upper Eocene beds.Most previous studies on fossil Ochotonidae are limited to teeth due to the fragile and very thin bones on the skull and poor preservation.Hence complete fossil material is particularly pending for the better understanding of the morphology and evolution.A large number of exquisitely preserved skulls of lagomorphs were unearthed recently from the late Oligocene strata of area C,langhaogou,Saint-Jacques,in Bayan Nur city,Inner Mongolia.These fossils constitute the key materials of this thesis.These skulls are by far the most complete Paleogene Ochotonidae.Based on detailed observation and comparisons with other known fossil materials,we identified the materials as Sinolagomys ulungurensis.We described as much details as possible every bones of the skulls,recognised the morphological features,such as the overall size of the skull,the features of every bones,and the connections to other parts.Measurable parameters on the skulls were carefully recorded under the microscope.Finally,we reconstructed the 3D image with CT scanning date for better showing the skull morphology.Morphological characteristics of the teeth were also recorded in detail,including upper and lower cheek teeth and incisors.The complete skulls with upper and lower jaws articulated in situ improve the identification of previous described broken and isolated fossils.Living environment and feeding habits are often reflected by some morphological characteristics of animals.We deduced the ecological environment and feeding habits of Sinolagomys by the morphological characteristics of the skull,such as zygomatic arch morphology,width of frontal and parietal bone,interorbital breadth and orbital size.In this paper,we presented the detailed morphology of the earliest skull of Ochotonidae,improved the identification features of Sinolagomys,and further provided important information for understanding of the orgination and development of Ochotonidae.