Late Miocene Hipparionine Fossils From The Lamagou Fauna Of Fugu,Shaanxi Province

Wangdafuliang section is the most classical "Hipparion Red Clay" sequence of northern Shaanxi,at Logaochuan,Fugu,Shaanxi Province.Thousands of well preserved fossils of Hipparion fauna were found from the section,they're priceless late Miocene-early Pliocene fossils and also a key window on learning about paleontology,stratigraphy,palaeoecology,etc.Hipparionine horse especially has significant value on evolutionary biology,stratigraphy,and palaeoecology as the index fossil of Cenozoic strata.In consequence,hundreds of hipparionine fossils from the lower fossil bed(named Lamagou fauna,and with a dated age of approximately 7.4 Ma)in Wangdafuliang were studied systematically in the dissertation.At first the morphology of the fossils are researched:(1)The 11 skulls,17 mandibles,and 26 pieces/groups of postcranial bones were described;(2)Comparing with relative specimens which hang at institute of vertebrate paleontology and paleoanthropology(IVPP).Conclusions are as follows:(1)All of these fossils are belongs to Hipparion chiai;(2)Still there are some differences between them and the H.chiai which from Lantian;(3)A direction and polars were given by the comparison among the members of Hippotherium(Hipparion)subgenus.The link had also been shown between Hippotherium(Hipparion)and Hipparion(Hipparion)subgenus,the H.chiai from the Lamagou Fauna may be the transitional type between Bahean and Baodean age.A key problem in taxonomy of hipparionine horses is the high intraspecific variations and the less obvious species differences,and the occlusal structural change with dental wear is one of the great causes of these.A collection of 28 hipparionine skull and mandible fossils from the Lamagou Fauna shows an age distribution in a successive development sequence.By observing the dentitions in these fossil materials,knowledge of dental ontogeny has been gained,such as the opening time of the posterior wall of post-fossettes,the displacement of the plis hypostyle,the morphologic changes of the protocone and hypocone,etc.Additionally,CT technology and traditional sectioned cheek teeth were used for authentication.These discoveries indicate that the hipparionine species in the Lamagou fauna is only H.chiai exactly and offer further insight into the morphologic changes that occur during dental wear,which may greatly promote the morphological and taxonomic study.In further experiments,the paleoecology and the paleoclimate of Fugu area in-7.4 Ma were reconstructed by kinesiology of horse and fossil tooth enamel stable isotope:(1)The paleoecologic setting of the Fugu region were open steppe and dominated by C3 plants;(2)It had distinct seasons and affected by the end of what was then the Asian monsoon system.