The evolution of extreme hypercarnivory in Metriorhynchidae (Mesoeucrocodylia: Thalattosuchia): evidence from microscopic denticle morphology and a new tri-faceted Kimmeridgian tooth from Germany

ANDRADE, M.; YOUNG, M.; DESOJO, J.B.; BRUSATTE, S.

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Lugar: Illinois, USA; Año: 2010

0272-4634

Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs.The derived genera Dakosaurus and Geosaurus exhibit a macroevolutionary trendtowards hypercarnivory, underpinned by a diverse array of craniodental adaptations,including denticulate serrated (ziphodont) dentition. A new Geosaurus tooth from theNusplingen Plattenkalk of Germany provides evidence for a previously unknownlarge species and extends the range of ziphodonty in Geosaurus into theKimmeridgian. A comparative analysis of serrations in Metriorhynchidae shows thatknown Dakosaurus species had conspicuous denticles, which contrast with themicroscopic denticles of Geosaurus. Metriorhynchid specimens from the upperKimmeridgian-lower Tithonian of Bayern and Baden-Württemberg, Germany, showthat ziphodont species of Dakosaurus and Geosaurus co-occurred in the Nusplingenand Solnhofen Seas. Although these genera converge on denticulate dentition, theydiverge on overall crown morphology. As such, resource/niche partitioning viacraniodental differentiation is posited as maintaining two contemporaneous genera ofhypercarnivorous metriorhynchids. Additionally, the new generic name Torvoneustesis proposed for “Geosaurus” carpenteri, the only known metriorhynchid with falseziphodontdentition. A cladistic analysis shows that ziphodont dentition may haveevolved independently in Dakosaurus and Geosaurus, or acquired earlier by theircommon ancestor and secondarily lost in Torvoneustes and related taxa.