Study On The Squamata And Rhynchocephalia From The Upper Cretaceous Nenjiang Formation In Songliao Basin,Northeast China

The Songliao Basin is located in Northeast China.Its well-preserved lacustrine deposits provide a nearly continuous continental Cretaceous stratigraphic sequence,which is an ideal place for studying the Cretaceous terrestrial biomes and ecosystems in Northeast China.However,we still know very little about the composition of the Cretaceous terrestrial vertebrates in the Songliao Basin,especially about the small reptiles such as squamates and rhynchocephalians,for which there have been no definite research reports in the past.In this paper,new fossil materials of squamate and rhynchocephalian from the Upper Cretaceous Nenjiang Formation in the Songliao Basin were studied.Eleven squamate fossils were involved,four of which were identified as three groups of Scincomorpha(similar to paramacellodid,xantusiid and scincid),and two of which were identified as one group of Laterata(similar to lacertid),the remaining five pieces cannot be further identified.One rhynchocephalian fossil was identified as Sphenodontinae gen.et sp.indet.1)Scincomorpha(RCPS-VJ3011-3013,RCPS-VH3001).The crown of RCPS-VJ3011 and RCPS-VJ3012 are blunt and unicuspid,and the lingual side is concave,with fine lingual striations developed;the cusps labialis and lingualis are connected by the straight ridge of the carina intercuspidalis;the cristae mesialis and distalis are unequal in length;the bases of the teeth are expand labiolingually;which is similar to that of paramacellodids.RCPS-VJ3013 resembles xantusiids by the end of cristae mesialis and distalis extending to the lingual side of the tooth and the lingual side of the tooth crown is convex,etc.RCPS-VH3001 resembles scincids due to the following characteristics: the tooth is conical and unicuspid,the tooth crown is lingually concave,cristae mesialis and distalis gradually transform into culmen lateris and extend to lingual surface.2)Laterata(RCPS-VH3002-3003).RCPS-VH3002 can be classified into Laterata based on its heterodont dentition composed of unicuspid,bicuspid and tricuspid teeth,with the anterior cuspid is larger than the posterior cuspid,which is similar to lacertids.RCPS-VH3003 has slender teeth with tricuspid crowns;the anterior cuspid is larger than the posterior cuspid.It can be arranged into Laterata,similar to lacertids.3)The fossil specimens of RCPS-VJ3014-3018 preserved little information,and their precise classification cannot be determined,they are tentatively referred to Squamata incerti subordinis.4)The fossil material RCPS-VJ3019 of rhynchocephalian is a jaw fragment.Additional teeth have a large square-based,the well-developed anterior flanges and weak posterior flanges produce imbrication,indicating that it belongs to sphenodontines.Based on the characteristics of the morphology and size of the specimens,it can be inferred that the Late Cretaceous squamates in the Songliao Basin were mainly small individuals with carnivorous and omnivorous feeding habits.The Late Cretaceous squamate fauna in the Songliao Basin is similar to that in North America,Mongolia and Inner Mongolia in China,and the related fauna may have interchanged during or before the Late Cretaceous.Both squamate and rhynchocephalian were discovered for the first time in the Late Cretaceous of Northeast China,which are of great importance for understanding the taxonomic diversity,faunal composition and paleogeographic distribution of the Late Cretaceous vertebrates in the Songliao Basin and Northeast China.