The Quantitative Phylogenetic Analysis Of Mamenchisaurus Anyuensis

Sauropods are the most important dinosaur category for their extensivedistributing both geological and geographcal distribution,and they are the biggestterricolous vertebrate among the history of the earth.And Sichuan Basin is one of thearea that has most abundant sauropod fossils.Mamenchisaurus,as a famous member ofsauropod, was particularly exist in Jurassic of East Asia.Most of its fossils werediscovered in Sichuan Basin and have great significance.Through the research ofMamenchisaurus,we can reappear the organic sphere looks of Jurassic and thepaleoenvironment,and discuss the evolution law of dinosaurs.The material which this text is research about is the fossils of Mamenchisaurusanyuensis,a kind of sauropod from Late Jurassic of Anyue,Sichuan.The fossils ofMamenchisaurus anyuensis include many individuals from two points,and theirgeological horizon are Suining Formation and Penglaizhen Formation.These are thehighest geological horizon of Late Jurassic dinosaur fossils.It fill up the blank ofstratum with dinosaur fossils in Sichuan Basin,and is of great importance.It provideprecious information about paleoenvironment and paleogeography of Jurassic.Mamenchisaurus anyuensis has high geological horizon and some uniquefeatures,so we can not rule out the possiblility that it can found a new genus.This textmake comparison of Mamenchisaurus anyuensis and other species ofMamenchisaurus,and other kinds of sauropod.It was found that Mamenchisaurusanyuensis and other species of Mamenchisaurus are similarly in many basicfeatures:posterior cervical and anterior dorsal neural spines are bifid,presacral centraare opisthocoelous,anterior caudal centra are procoelous,and so on.And the mostimportant unique features of Mamenchisaurus anyuensis are:First,some of its toothabsent marginal denticles on posterior edge while other tooth absent marginal denticles on both anterior and posterior edges.Second,its posterior cervical andanterior dorsal bifid neural spines have median tubercle,this feature are absent in allother sauropods of Sichuan Basin but present in Diplodocus and Euhelopus.And thethird,its presacral centra are quite spongy,pleurocoels developed well.It may representbetter ability of movement.In order to certain the phylogenetic position of Mamenchisaurus anyuensis,thistext do the Quantitative phylogentic analysis of it.The software in use is NONA,andthe character library includes234characters.29kinds of sauropod and an outgroupwere put in analysis.The result of analysis show that Mamenchisaurusanyuensis,Mamenchisaurus youngi and Mamenchisaurus hochuanensis consist of amonophyletic group.And compared to Mamenchisaurus hochuanensis,Mamenchisaurus anyuensis is more close to Mamenchisaurus youngi.We can say thatMamenchisaurus anyuensis is the most advanced species of Mamenchisaurus genus.We can also found in the analysis result that the so-called "Mamenchisauridae" or"Euhelopodidae" are not monophyletic group,and the means that divide the sauropodin two kinds by teeth morphology is not been suppport.This is similar with theanalysis result of most foreign researchers by recent years.