云南中三叠世一恐头龙科小型主龙型类OACSTPCD

Among numerous marine reptiles discovered in the Triassic eastern Tethys,today's Southern China,Dinocephalosaurus is a bizarre animal comparable to European Tanystropheus in developing a prominently long neck.These two taxa are respectively assigned to Dinocephalosauridae and Tanystropheidae,and the two families and other basal members collectively form an early-diverging clade of Archosauromorpha.Here we report a new archosauromorph specimen,IVPP V18579,excavated from the lower Middle Triassic(Anisian),from Luoping,Yunnan in southwestern China.Compared with all the hitherto known dinocephalosaurids and tanystropheids,this skeletally mature individual is exclusively similar to Dinocephalosaurus in a number of characteristics,particularly with the long posterodorsal process of the premaxilla extending posteriorly beyond the level of the external nares,the concave posterior margin of the anteroposteriorly broad quadrate,and the strongly expanded distal end of the chevron in most of the caudal vertebrae.However,this reptile is much smaller than Dinocephalosaurus and different from Dinocephalosaurus and the other dinocephalosaurid,Pectodens,in many aspects,such as an anteriorly tapering long rostrum,the dentition composed of short conical teeth with less heterodonty,relatively but obviously tall neural spines of the axis and the anterior cervical vertebrae.Our phylogenetic analysis suggests that the new archosauromorph is a dinocephalosaurid,and then we erect Austronaga minuta gen.et sp.nov.based on this specimen.Detailed comparisons in osteological anatomy and the discussion about its potential aquatic adaptation of this new taxon are also provided.