Boionautilus gen. nov. from the Silurian of Europe and North Africa (Nautiloidea, Tarphycerida)

Bulletin of geosciences

Turek V¹ 

关键词: Cephalopoda;    Nautiloidea;    Tarphycerida;    new taxon;    Silurian;    Europe;    North Africa;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

TarphyceridsofthesuborderBarrandeocerinaarestrikingowingtothelargesizeoftheshellandsimilaritywiththerecentAllonautilusWardSaunders,1997.TheyarewidelydistributedintheSilurianrocksofEurope.TheywereoriginallyclassifiedwithinthegenusNautilusLinnaeus,1758butgenericassignmentremainedquestionabledespitethedetaileddescriptionandexcellentillustrationprovidedbyBarrandein1865.SpeciesbelongingtothisgrouphavebeenassignedtothegeneraBarrandeocerasHyatt,1884,HeraclocerasTeichert,1940,orCumingsocerasFlower,1950butnoneofthemisappropriateconsideringtheirmorphology,phylogenetictrendsandstratigraphicrange.Therefore,anewgenusBoionautilusisestablishedhere.Anevolutionarytrendisdiscerned,expressedespeciallyinthetightercoilingoftheshell-atransitionfromanevoluteshell(gyroceraconeatthebeginningofthesecondwhorl)withsubellipticcrosssection,toaslightlyinvoluteshellwithasubtrapezoidalcrosssection.Thedorsoventraldiameterofthewhorlincreasedmorerapidly,andseptabecamemoredenselyspaced.Boionautilustyrannus(Barrande,1865)isnowknowntooccurinNorthAfrica(Algeria,theOugartaRange).Previously-mentionedfindsinperi-GondwanansedimentsoftheCarnicAlpsarehererejected.Differencesinthecolourofseptaandconnectingringsinoneexceptionallywell-preservedspecimenofthistaxonfromAlgeriaandoneBohemianspecimenofB.sternbergi(Barrande,1865)areremarkableandindicatehighprimarycontentoforganicmatterwithintheconnectingrings.

【 授权许可】

Unknown