The endemic and morphologically remarkable nautilid genus Deltocymatoceras Kummel, 1956 from the Late Cretaceous of Central Europe

Bulletin of geosciences

Wilmsen M¹  Frank J¹  Košťák M¹ 

关键词: Nautilida;    taxonomy;    phylogeny;    ontogeny;    palaeogeography;    functional morphology;    biostratigraphy;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

TheendemicLateCretaceousnautilidgenusDeltocymatocerasKummel,1956isrepresentedbyDeltocymatocerasleiotropis(Schlüter,1876)andD.rugatum(Fritschnbsp;Schlönbach,1872).Characteristicforthisgenusisabulbousinvoluteshellwithstrongradialribbingandaventralkeel,whichappearsinpost-juvenileontogeneticstages.Thecombinationofthesemorphologicalfeaturesisuniqueamongpost-Palaeozoicnautiloids.BothspeciesarerestrictedtotheLateTuronian–MiddleConiacianofCentralEuropeandEngland.Untilnow,thetypespeciesD.leiotropiswasknownbasedonlyontheholotypespecimen.Thisspecimenisre-describedwithrevisedoccurrenceandforthefirsttimephotographicallyillustrated.TheonlypreservedsyntypefromthetypespecimensofD.rugatumwasre-discoveredduringthisrevisionandmorethanthirtyotherspecimenswerestudied.RepresentativesofDeltocymatocerasshowclearmorphologicalchangesduringtheirontogenyandacquisitionofmaturity,mostnotablytheappearanceofaventralkeelinprematurestagesanditsdisappearanceatmaturity.ThehypothesisofaclosephylogeneticaffinityofDeltocymatocerastothegenusCymatocerasHyatt,1884isbasedonsimilarmorphologicalfeaturessuchasthesuture,ribbing,shellshapeandearlyontogeneticdevelopment.Theventralkeelisquiteanexceptionalfeatureofmorphologyinpost-Palaeozoicnautiloids.InparticularthecombinationwithaninvolutedepressedshellisonlysharedwithrepresentativesofthegenusAngulithesMontfort,1808(Cretaceous–Palaeogene)andGryponautilusMojsisovic,1902(Triassic).ThecombinationwithacompressedandevoluteplanispiralshellismorecommoninPalaeozoicandsomepost-Palaeozoicnautiloids.Theventralkeelisdiscussedhereinrelationtoitsfunctionalaspects(hydrodynamicstability)incombinationwiththestrongradialribbing(protectionoftheshellagainstmechanicaldamage).TheappearanceofthegenusconcurredwiththelateTuronianshallowing/coolingassociatedwiththe“HyphantocerasEvent”andtheavailabilityofanecologicniche(i.e.,absenceofmedium-sized,keeledammonitesatthattime).Lowabundance,anendemicoccurrence,andtheveryshortstratigraphicrangeofthegenus(~3.5Ma)reflectthelimitedevolutionarysuccessoftheDeltocymatoceraslineage.

【 授权许可】

Unknown