The alleged astragalar remains of Didolodus Ameghino, 1897 (Mammalia, Panameriungulata) and a critic of isolated bone association models

Bulletin of geosciences

Gelfo JN¹  Lorente M¹ 

关键词: South America;    Paleogene;    Didolodontidae;    astragali;    regression equation models;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

PostcranialcharactersofSouthAmericannativeungulatesareimportantinordertoanalyzetheirrelationshipsintheactualtheriantaxonomy,particularlytotesttheirallegedafrotherianaffinities.Inthissense,themostprimitiveandoldestSouthAmericaneutheriansarerepresentedbytwoendemicgroupsof“condylarths”,theKollpaniinaeandDidolodontidae.Theseforms,characterizedbylowercrownedbunodontdentition,haveneverbeenfoundindirectassociationwiththeirpostcranialremains.Eventhough,severalskeletalelementshavebeenassignedtosomeofforms,followingdifferentassumptionsandcriteria.Twodistinctastragalarremains(MACN-CA10737andAMNH117457)havebeenreferredtothegenusDidolodus,oneofthemostcommondidolodontidsfromearlyandmiddleEocenePatagonianoutcrops.Herewedescribeindetailandillustratethesematerials.Acriticalanalysisismadeofseveralregressionequationmodelswhichhavebeenusedinothercasestoassociatebysizeisolatedpostcranialelementstotaxadefinedbyteeth.Anewmodelwasformulatedbasedon19modernbunodontmammalswithdirectlyassociatedskeletonsinordertotesttheaccuracyoftheregressionequations.AlthoughtheresultsoftheequationmodelsfailedtoaccuratlyassignedtheisolatedastragalitoanyoftheDidolodusspecies,theycanbeusedasagoodtooltodisprovetheassociationhypothesis.AbroadcomparisonwithastragalarremainsofSouthAmericannativeungulatesindicatesthatMACN-CA10737hasnotoungulateaffinities,incontrastAMNH117457resemblestheastragaliassignedtodidolodontidsfromSaoJosédeItaboraí,Brazil,accordingtothemodelscriticizedhere.Thesimilitudeisparticularlyduetothebroaddevelopmentofthecotylarfossa,acharacterproposedasanafrotheriansynapomorphy,butprobablydevelopedindependentlyindifferentgroups.ImprovementinknowledgeregardingpostcranialcharactersoftheearliestSouthAmericannativeungulatesisnecessarynotonlyduetoitsimportanceinimprovingaccuracyofphylogeneticrelationships,butalsofortheinferencesmadeonpaleobiologicalfeatures.

【 授权许可】

Unknown