云南东部中三叠世始鳍龙类—新属种(英文)

根据一保存完整的骨骼(包括头骨、下颌和全部头后骨骼)建立了鳍龙类的一新属新种——利齿滇东龙(Diandongosaurus acutidentatus gen.et sp.nov.)。标本采自云南省罗平县中三叠世安尼期关岭组上段。新属种既具有肿肋龙类(包括Dactylosaurus,Anarosaurus,Serpianosaurus和Neusticosaurus)吻部两侧不收缩、眶前区域长于眶后区域、眼眶大于上颞孔等典型特征,同时又具有幻龙类(包括Simosaurus和nothosaurians)前颌和下颌前部犬齿型齿发育、上颌具1或2个犬齿型齿等典型特征。新种的额骨和顶骨均愈合,额骨两后外侧支的末端后延超过上颞孔前缘,轭骨和鳞骨相交将眶后骨排除于下颞孔之外,方轭骨发育,锁骨前外侧缘具一突起,3对荐肋以及最前部尾肋的外侧端均未见明显收缩。这些特征也多表现出肿肋龙类和幻龙类的混合特征。此外,新种还具有一些较为独特的特征,包括前额骨和后额骨沿眼眶背缘相交,第3至第8对尾肋的长度超过荐肋,后肢末端发育异常膨大的爪趾骨。系统关系分析表明,滇东龙既不是肿肋龙类也不是幻龙类;它可能与由乌蒙龙、幻龙类和传统的肿肋龙类所构成的分支亲缘关系最近,为始鳍龙类基干类群。

A NEW EOSAUROPTERYGIAN FROM MIDDLE TRIASSIC OF EASTERN YUNNAN PROVINCE, SOUTHWESTERN CHINA

A new eosauropterygian,Diandongosaurus acutidentatus gen.et sp.nov.,is described based on a skeleton from the Upper Member of Guanling Formation (Middle Anisian) of Luoping County,Yunnan Province,southwestern China.This new species displays a combination of traits seen in nothosauroids (Sirnosaurus and nothosaurians) and pachypleurosaurs (Dactylosaurus,Anarosaurus,Serpianosaurus,and Neusticosaurus).It has an unconstricted snout,preorbital region longer than the postorbital region.and a supratemporal fenestra smaller than the orbit,as in the pachypleurosaurs.On the other hand,it hears enlarged and procumbent teeth in the premaxilla and the anterior dentary,and one or two fang-like maxillary teeth,as in the nothosaurs.In this new species,the frontals and the parietals are fused,the posterolateral process of the frontal extends posteriorly over the anterior margin of the supratemporal fenestra,the postorbital is excluded from the infratemporal fenestra by the jugal-squamosal contact,the quadratojugal is present,the clavicle has an anterolateral projection,and the three sacral and anterior caudal ribs are distally pinched off but not constricted.Unlike in most of other stem eosauropterygians,the prefrontal and the postfrontal meets each other along the dorsal margin of the orbit,the descending ramus of the squamosal reaches the articular condyle of the quadrate,caudal ribs 3 to 8 are elongate and longer than sacral ribs,and the ungual phalanxes of the pes are extremely dorsoventrally expanded.Our phylogenetic analysis suggests that Diandongosaurus is neither a pachypleurosaur nor a nothosauroid;it might be the sister group of the clade consisting of Wumengosaurus,the nothosauroids and those taxa traditionally considered as pachypleurosaurs.