Xinpusaurus: Difference between revisions

| fossil_range = [[Late TriassicCarnian]], {{fossil_rangefossil range|Carnian232|228}}

* {{extinct}}''X. xinyiensisxingyiensis'' <small>Li ''et al.'', 2016</small>

'''''Xinpusaurus''''' is an extinct [[genus]] of [[thalattosaur]] from the [[Late Triassic]] of [[Guanling]] in [[Guizhou, China]]. Several species have been named since 2000: the [[type species]] ''X. suni'' along with the species ''X. bamaolinensis'' and ''X. kohi''. A 2013 study proposed that all three species are [[synonym (taxonomy)|synonymous]] with each other, in which case ''X. suni'' would be the only valid species, although a 2014 study argued that ''X. kohi'' was also valid.<ref name=LJ13>{{cite journal |last=Liu |first=J. |year=2013 |title=On the taxonomy of ''Xinpusaurus'' (Reptilia: Thalattosauria) |journal=Vertebrata PalAsiatica |volume=51 |issue=1 |pages=17–23 |url=http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/201301/P020130131404692609056.pdf}}</ref><ref name=":0">{{Cite journal|url=http://www.palaeodiversity.org/pdf/07/04Palaeodiversity_7-14_Maisch_3.pdf|title=On the morphology and taxonomic status of ''Xinpusaurus kohi'' JIANG et al., 2004 (Diapsida: Thalattosauria) from the Upper Triassic of China|last1 = Maisch | first1 = M.W. | journal = Palaeodiversity | volume = 7 | pages = 47–59 | date = 2014}}</ref> A fourth species, ''X. xinyiensisxingyiensis'', was described in 2016.<ref name=":1">{{Cite journal |lastlast1=Li |firstfirst1=Z.-G. |last2=Jiang |first2=D.-Y. |last3=Rieppel |first3=O. |last4=Motani |first4=R. |last5=Tintori |first5=A. |last6=Sun |first6=Z.-Y. |last7=Ji |first7=C. |date=2016-11-01 |title=A new species of Xinpusaurus (Reptilia, Thalattosauria) from the Ladinian (Middle Triassic) of Xingyi, Guizhou, southwestern China |url=https://www.researchgate.net/publication/309411833 |journal=Journal of Vertebrate Paleontology |volume=36 |issue=6 |pages=e1218340 |doi=10.1080/02724634.2016.1218340 |bibcode=2016JVPal..36E8340L |issn=0272-4634 |s2cid=132418823}}</ref>

''Xinpusaurus'' is a thalattosaur, a group of triassic marine reptiles with long, paddle-like tails and short legs with independently movable digits. Specifically, it is a member of the group thalattosauroidea, which are characterized by their downturned [[premaxilla]]e. ''Xinpusaurus'' had a short neck, a massive [[Quadrate bone|quadrate]], and one of the few braincases preserved in thalattosaurs. The lower jaws of this genus show two different forms of [[dentary]]-[[Suprangular|surangular]] sutures, either a v-shaped suture with the surangular cutting into the dentary from the side (type 1) or an oblique suture with the surangular underlying the dentary (type 2). ''X. bamaolinensis'' preserves a type 2 suture while ''X. kohi'' has a type 1 suture. ''X. suni''<nowiki/>'s suture differs between specimens while ''X. xinyiensisxingyiensis'' seems to have a type 2 suture.<ref name="LJ13" /> The dentary is also narrow and shorter than the snout, with robust, pointed teeth in the front of its jaws and broad crushing teeth in the back of its jaws, suggesting that it fed on hard-shelled prey, although these adaptations are not as extreme as those of ''[[Concavispina]]'', which had exclusively short and blunt teeth.<ref name="LZLH13">{{Cite journal|last1=Liu|first1=J.|last2=Zhao|first2=L. J.|last3=Li|first3=C.|last4=He|first4=T.|year=2013|title=Osteology of ''Concavispina biseridens'' (Reptilia, Thalattosauria) from the Xiaowa Formation (Carnian), Guanling, Guizhou, China|journal=Journal of Paleontology|volume=87|issue=2|pages=341|doi=10.1666/12-059R1.1|pmc=|pmid=|bibcode=1974JPal2013JPal...4887..524M341L |s2cid=83684967}}</ref> This genus also has a uniquely upward-curving [[maxilla]], a wide proximal end of the [[humerus]], and a [[Radius (bone)|radius]] with a convex lateral edge and concave medial edge.<ref name=":1" />

''X. bamaolinensis'' and ''X. kohi'' had particularly elongated premaxillae, forming a narrow and pointed [[Rostrum (anatomy)|rostrum]]. However, it should be noted that the specimens with the longest snouts are also the smallest in other proportions, so this may be a juvenile trait and cannot be used to distinguish these species from ''X. suni''.<ref name="LJ13" />

''X. xinyiensisxingyiensis'' is the largest species known and is also probably the least advanced, as it does not have a posterior process of the jugal unlike the other species and shares some similarities with the genus ''Concavispina''.<ref name=":1" />

''Xinpusaurus kohi'' was described in 2004 from GMPKU 2000/05, an incomplete skeleton. This specimen was also found in two slabs, with the rear slab missing most of the hindlimbs and possibly not belonging to the same individual as the first. In addition, there is evidence that some of the bone structure near the break has been tampered with and that most of the pelvic material has been lost. A 2013 analysis showed that many of the traits initially believed to differentiate ''X. kohi'' from ''X. suni'' were inaccurate, either due to incomplete data, misidentification, or poor preservation.<ref name="LJ13" /> However, a redescription in 2014 resurrected the legitimacy of the species. This redescription provided additional diagnostic features and argued that the alterations were relatively minimal and that the posterior slab was almost certainly from the same individual as the anterior one.<ref name=":0" />

''Xinpusaurus xinyiensisxingyiensis'' was described in 2016 from XNGM WS-53-R3, a nearly complete articulated skeleton from the Zhuganpo member of the Falang formation.

{{Thalattosauria|N.}}