A Silurian oncocerid with preserved colour pattern and muscle scars (Nautiloidea)

Bulletin of geosciences

Turek V¹  Manda Å ¹ 

关键词: Nautiloidea;    Oncocerida;    colour pattern;    muscle scars;    Silurian;    Prague Basin;    new taxa;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

AnewgenusEuryrizocerina(Nautiloidea,Oncocerida,Oonoceratidae)fromthelateSilurianstrataofBohemia(PragueBasin)isestablished.Twospeciesareincludedwithinthegenus:thetypespeciesE.normata(Barrande,1877)andE.pulchrasp.nov.Thegenusisstrikingfortwofeatures–thepreservationofshellcolourationandmuscleattachmentscarsinthetypespecies.Thesefeaturesarereliablefortaxonomicandpalaeoecologicalanalysisofnautiloids,butduetotheironlyoccasionalpreservationinfossils,theevolutionarytrendsofthesecharactersremainpoorlyunderstood.ThecolourpatternofEuryrizocerinaconsistsofirregularpulsedtransversebandsthatclearlydifferfromthecolourpatternsknowninotheroncoceridswhereratherregularwave-likeorzig-zagbandshavebeenobserved.Itisquestionablewhetherthenewtypeofcolourationrepresentsataxonomicormorphotypicfeature,asEuryrizocerinaisthefirstoncoceridtoberecognisedwithahighlycurvedshellthatretainscolouration.Oncoceridsexhibitmultiplepairedmusclescarsandthereisuncertaintywhethertheserepresentanoriginalmetamery,inheritedfromacephalopodancestor,oraderivedfeature.Euryrizocerinapossessesfourpairsofretractormusclescars,butitsancestor“Oonoceras”fraternumandalliedforms,possessmultiplepairsofmusclescarsaroundthebaseofthebody-chamber,asdothemajorityofoncocerids.AsimilarreductioninthenumberofmusclescarpairshasbeendocumentedinDevonianrutoceratoids.Thehighevolutionaryplasticityofmuscleattachmentspatterns,asindicatedbytheseexamples,suggeststhatthemusclecomplexanditsattachmenttotheshellwasunderadaptivecontrolandismorelikelytoreflecttheformoftheshellandthemodeoflifeoftheorganism.Itseemslikelythatshellcolourationandthepatternofattachmentoftheretractormuscleshaveamuchmorecomplexevolutionaryhistory(includingseveralconvergences)thanwaspreviouslysupposed.

【 授权许可】

Unknown