Skull anatomy of Dakosaurus andiniensis (Thalattosuchia: Crocodylomorpha) and the phylogenetic position of Thalattosuchia

Abstract

Synopsis New information on Dakosaurus andiniensis from the Latest Jurassic and Early Cretaceous is reported here. One of the specimens described herein consists of an almost complete skull and lower jaw found in the uppermost levels of the Vaca Muerta Formation (Tithonian) of Neuquén Province, Argentina. The new material allows a more complete understanding and diagnosis of this form, previously known only from the fragmentary type specimen. The new remains show that D. andiniensis had an unusual morphology for a marine crocodyliform,namely a remarkably short, high snout with ziphodont dentition. This new information allows testing of the phylogenetic relationships of this taxon, which is depicted as deeply nested within Metriorhynchidae, a clade of marine crocodyliforms with derived adaptations to the marine environment (e.g. paddle‐like forelimbs, hypertrophied nasal salt glands). In particular, D. andiniensis is inferred to be the sister taxon of D. maximus from the Jurassic of Europe. This relationship repeats the phylogenetic pattern seen in other Jurassic marine crocodyliforms from South America and Europe (e.g. Geosaurus), demonstrating the close faunal relationship between these two distant marine basins. The phylogenetic analysis reported here results in a most parsimonious hypothesis that depicts Thalattosuchia nested within Neosuchia and the strength and character evidence supporting this position is presented. In addition, several characters traditionally postulated as dependent upon the longirostrine morphology are critically examined under the light of new evidence. Most of them show a character state distribution that is not strictly compatible with that of the longirostrine condition and, therefore, are interpreted as independent units of phylogenetic evidence.