A new species of compsognathid from the Early Cretaceous Yixian Formation of western Liaoning, China

HU Yuanchao, WANG Xuri, HUANG Jiandong

(1. Geological Museum of Anhui Province, Hefei 230031, Anhui, China; 2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)



A new species of compsognathid from the Early Cretaceous Yixian Formation of western Liaoning, China

HU Yuanchao1, WANG Xuri2, HUANG Jiandong1

(1.GeologicalMuseumofAnhuiProvince,Hefei230031,Anhui,China; 2.InstituteofGeology,ChineseAcademyofGeologicalSciences,Beijing100037,China)

Abstract:The paper reports a new genus and species of compsognathids: Beipiaognathus jii (gen. et sp. nov.). It possesses not only the diagnostic characters of Compsognathidae, such as the fan-shaped dorsal neural spines and robust phalanx Ⅰ-1, but also some unique characteristics different from other compsognathids, including the un-serrated conical-shaped teeth, relatively long ulna, robust and long phalanx Ⅱ-1, and relatively short tail. The discovery further reveals the great diversity of Compsognathidae and provides more information for understanding the anatomical characters of compsognathids.

Keywords:Coelurosauria; Compsognathid; Early Cretaceous; Yixian Formation; Western Liaoning

0Introduction

Compsognathidsareasmallgroupofmoderatelyprimitivetheropods,commonlyplacedatthebasalpositionwithinCoelurosauria(Sereno, 1999;Rauhut, 2003;Holtzetal., 2004;Norelletal., 2005).Compsognathidae,originallynamedbyCope(1871),isdefinedasCompsognathus longipesandalltaxasharingamorerecentcommonancestorwithitthanwithPasser domesticus.CompsognathidsarecurrentlyknownfromEurope,SouthAmericaandChina,rangingfromtheLateJurassictotheEarlyCretaceous(Peyer, 2006).InformationaboutcompsognathidhasbeenknownonlyfromCompsognathusforalongtime.ButthediscoveryofSinosauropteryx (Jietal., 1996;Chenetal., 1998;Currieetal., 2001), Huaxiagnathus (Hwangetal., 2004)andSinocalliopteryx (Jietal., 2007)fromtheEarlyCretaceousYixianFormationofChinahasgreatlyaidedourunderstandingoftheiranatomy.Compsognathidaecurrentlyconsistsof8taxa: Compsognathus longipes, Aristosuchus pusillus (Owen, 1876), Sinosauropteryx prima (Jietal., 1996), Scipionyx samniticus (Daletal., 1998), Huaxiagnathus orientalis (Hwangetal., 2004), Mirischia asymmetrica (Naishetal., 2004), Juravenator starki (Göhlichetal., 2006)andSinocalliopteryx gigas (Jietal., 2007).

Herein,wereportanewcompsognathidspecimenuncoveredfromtheEarlyCretaceousYixianFormationofWesternLiaoning,China.Thenewspecimenwaspreservedalmostcompletelyinrightlateralview.ItcanbeassignedwithinCompsognathidaebypossessingfan-shapeddorsalneuralspines,proximalwidthofphalanxI-1morethanminimalshaftdiameterofradius(Chenetal., 1998;Peyer, 2006).ItismoresimilartoHuaxiagnathusandSinocalliopteryxbypossessinglargeandsub-equalungualsofthefirsttwomanualdigits.Thischaracterhasonlybeenobservedinthesethreespeciesuptodate.Furthermore,thenewspecimenhassomeuniquecharacteristics,suchastheun-serratedconicalteeth,relativelylongforelimbduetothelongerulna,andtherobustlongphalanxⅡ-1.Basedontheanatomicalcharacteristicsandcomparisonswithothercompsognathids,weerectanewgenusandspecies: Beipiaognathus jii (gen.etsp.nov.).

1Systematic descriptions

TheropodaMarsh, 1881

TetanuraeGauthier, 1986

CoelurosauriavonHuene, 1914

CompsognathidaeMarsh, 1882

Beipiaognathus jiigen.etsp.nov.

Etymology:Thegenusnameisderivedfromthefossillocality:BeipiaoCityofWesternLiaoning,China;thespecies′nameisinhonorofProf.JIQiangforhiscontributionstothestudyofcompsognathids.

Holotype:AGB4997 (AnhuiGeologicalMuseum,Hefei,AnhuiProvince),anearlycompleteskeletonpreservedinrightlateralview(Fig.1,Table1).

Fig.1　Photograph of the holotype of Beipiaognathus jii (gen. et sp. nov.)

Localityandhorizon:BeipiaoCityofWesternLiaoning,China;YixianFormationofEarlyCretaceous.

Diagnosis:Arelativelylargercompsognathid(1.6mlong)isdistinguishedfromothercompsognathidsbythefollowinguniquecharacteristics:teethareconical-likeandun-serrated;theforelimbisrelativelylong(forelimb/hindlimb=0.55)owingtotherelativelylongulna(femur/ulna=1.09);metacarpalIisshortandrectangular-shaped,about24%thelengthofmetacarpalⅡ;phalanxⅡ-1isthemostrobustandthelongest;pedaldigitⅢisthelongest,followedbydigitⅣandthendigitⅡ;tailisrelativelyshort,withnomorethan40caudalvertebrae.

Table 1　Measurements of main bones of

2Descriptions and discussions

TheskullofBeipiaognathus jii (gen.etsp.nov.)ispreservedinlateralview(Fig.2).Twopremaxillaryteethandtwodentaryteethcanbeobservedattheanteriorportion.Severalteethweremovedtotheposteriorportionoftheskullduetothepreservation.Allteethareconical-likeinshapeandun-serrated.ThemorphologiesoftheteetharetotallydifferentfromthoseofSinosauropteryx, HuaxiagnathusandSinocalliopteryx,whicharesharplybentposteriorlyandbearserrationsontheposteriorcarinae.

Fig.2　Detailed photograph of skull (a) and detailed photograph of un-serrated teeth (b) of Beipiaognathus jii (gen. et sp. nov.)d-dentary; fr-frontal; mx-maxilla; n-nasal; p-parietal; pm-premaxilla; t-tooth

Thevertebralcolumniscomposedof11cervical, 13dorsal,unknownnumbersofsacralandabout39caudalvertebrae.Numbersofthecervicalanddorsalcolumnsaresimilartothoseofothercompsognathids(Currieetal., 2001;Jietal., 2007),butthenumberofcaudalcolumnsislessthanthoseofSinosauropteryxandSinocalliopterxy (64and49,respectively) (Currieetal., 2001;Jietal., 2007).Theposteriorcervicalsbearshortandlowneuralspines,whichprominentlyareinclinedposteriorly.Thecervicalribsarerelativelylongandthread-likewithwidenedproximalends.Theneuralspinesofthedorsalsareanteroposteriorlyexpandeddistallysothattheyappearfan-shapedinlateralview,whichisoneofthesynapomorphiesofcompsognathids(Currieetal., 2001;Rauhut, 2003;Hwangetal., 2004;Naishetal., 2004;Jietal., 2007).Theiliumoverlappedtheproximaltailandthesacrum,soitishardtodeterminetheexactnumberofsacralcolumn.Presentlyabout39caudalvertebraecanbeobserved.Theanteriorcaudalshaveneuralspines,whichbecomeshorterandmoreinclinedposteriorly,buttheposteriorcaudalshavenoneuralspines.Thecentreoftheanteriorcaudalsarerobustandequalinheightandlength.Thecentraoftheposteriorcaudalsareslender,andtheirlengthislargerthantheheight.The21posteriorcaudalshavenoneuralspines.Chevronsprogressivelybecomeshorterandmoreinclinedposteriorly.

Fig.3　Detailed photograph of forelimbs of Beipiaognathus jii (gen. et sp. nov.)mcⅠ, Ⅱ-metacarpalⅠ, Ⅱ; phⅠ, Ⅱ, Ⅲ-phalanx Ⅰ, Ⅱ, Ⅲ

Theforelimbspreservedarealmostarticulated(Fig.3).Theyarerelativelylongandstout,withtheratioofforelimbtohindlimbis55%,whichisthehighestamongthecompsognithids.TheratioofforelimbstohindlimbsinCompsognathus, Sinosauropteryx, Huaxiagnathus, JuravenatorandSinocalliopteryxisabout39%, 36%, 48%, 50%and50%respectively(Bidaretal., 1972;Chenetal., 1998;Currieetal., 2001;Hwangetal., 2004;Göhlichetal., 2006;Jietal., 2007). Beipiaognathus jii (gen.etsp.nov.)hasrelativelylongforelimbs,becauseoftherelativelylargelengthoftheulna,whereasHuaxiagnathushasrelativelylongforelimbs,mainlyduetoitslongerhands.TheratioofhumerustoulnainBeipiaognathus jii (gen.etsp.nov.)isabout109%,buttheratioinHuaxiagnathusisabout160%.Thehumerusbearsadevelopeddeltopectoralcrestthatisdorsoventrallytwiceofthehumeralmidshaftdinameter.Thedistalendsofbothhumeriarerelativelyexpanded.Theulnaismorerobustandrelativelylongerthantheradius.ThisisdifferentfromthecharactersofHuaxiagnathusandSinocalliopteryx,inwhichtheulnaandradiusareslenderandsub-equalindiameter.

MetacarpalⅠisshortandnarrow,withthelengthalmosttwiceofthewidth.Itisrectangular-shaped,about24%thelengthofmetacarpalⅡ.ThemorphologyandratioofmetacarpalⅠtoⅡareverydifferentfromthoseofSinosauropteryx, HuaxiagnathusandSinocalliopteryx.ThefirstmetacarpalofSinosauropteryxisshortandbroad,extending

proximomediallyinanextensive

flange,andmorethan40%ofthelengthofthesecondmetacarpal(Currieetal., 2001).ThefirstmetacarpalofHuaxiagnathusisshortandstout,justunderhalfthelengthofthesecondmetacarpal(Hwangetal., 2004).ThefirstmetacarpalofSinocalliopteryxisstoutwithtransverselynarrowproximalend,anditisabout45%thelengthofthesecondmetacarpal(Jietal., 2007).MetacarpalⅡislongandrobust,whichisrelativelylongerthanmetacarpalⅢandmorethan4timesthelengthofmetacarpalⅠ.MetacarpalⅢislongerandslender.PhalanxⅠ-1isshorterandnarrowerthanphalanxⅡ-1andphalanxⅡ-2.ThisisdifferentfromcharactersofSinosauropteryx, HuaxiagnathusandSinocalliopteryx,inwhichPhalanxⅠ-1isthemostrobustandthelongestphalanx(Currieetal., 2001;Hwangetal., 2004;Jietal., 2007).Thefirsttwoungualsaresub-equalinsizeandmuchlargerthanthethirdungual.ThisissimilartothoseofHuaxiagnathusandSinocalliopteryx,butdifferentfromthatofSinosauropteryx,inwhichthefirstungualisthelargest.ManualdigitⅡisthemostrobustandthelongest,whichisverycommonamongtheropods.PhalanxⅡ-1isthemostrobustandthelongestphalanx,whichiswiderthantheradius.Thisisauniquecharacteristicamongthereportedcompsognathids.

ThehindlimbsofBeipiaognathus jii (gen.etsp.nov.)arewellpreservedandarticulated(Fig.4).Thefemurisrobustandrelativelystraight,onlyalittleboweddistally,whichis80%thelengthoftibia.Thestraighttibiaisthelongestboneofthisanimal,andthefibulaisslim,reachingtheankledistally.Amongthethreemainmetatarsals,metatarsalⅢisthelongest.Thefirstmetacarpalisshortandhighlypositioned.ThepedaldigitⅠendsabovethedistalendofmetatarsalⅢ.MetatarsalⅡandⅣarealmostonthesamelevelandsub-equalinlength.PedaldigitⅡisshorterthandigitⅣ.ThisisdifferentfromthatofHuaxiagnathusandSinocalliopteryx,inwhichdigitⅡandⅣaresub-equalinlength(Table2).

Fig.4　Detailed photograph of hindlimbs of

mtⅠ, Ⅱ, Ⅲ, Ⅳ-metatarsalⅠ, Ⅱ, Ⅲ, Ⅳ; Ⅰ, Ⅱ, Ⅲ, Ⅳ-pedaldigitⅠ, Ⅱ, Ⅲ, Ⅳ

3Conclusion

Onthebasisofthedescriptionsanddiscussionsabove,weconcludethatthecurrentspecimencanberecognizedasanewgenusandnewspecies: Beipiaognathus jii (gen.etsp.nov.),whichisthefourthcompsognathidtaxonfromtheEarlyCretaceousYixianFormationofWesternLiaoning,China.Thenewdiscoveryfurtherrevealthediversityofcompsognathidsandaidsmoreinformationforunderstandingtheanatomicalcharacteristicsofcompsognathids.

Acknowledgements

ThisworkwassupportedbythegrantsfromChinaGeologicalSurvey,intheformsof″PinasourianFauna,BiostratumanditsClassicalSectionsinNortheastChina″Project(12120114026801),and″DivisionandCorrelationoftheLateMesozicStratainWellSongke-Z″Project(121201102000150008-8).

Table 2　Comparisons of compsognathids uncovered in China

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Corresponding author:WANG Xuri. E-mail: wang198109@163.com

ManuscriptreceivedMar. 25, 2016;EditedbyCHENLu

Aboutthefirstauthor:HUYuanchao,male,seniorengineer,interestedincomprehensivestudyoffundamentalgeology.E-mail:yuanchaohu@163.com