Skull Anatomy of Dakosaurus andiniensis (Thalattosuchia: Crocodylomorpha) and the phylogentic position of Thalattosuchia

POL, D.; GASPARINI, Z.

Journal of Systematic Palaeontology

Cambridge Journals

Lugar: London; Año: 2009 vol. 7 p. 163 - 197

1477-2019

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, such as a remarkably short, high snout with ziphodont dentition.The new information allows testing 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, Dakosaurus andiniensis is inferred to be the sister taxon of Dakosaurus 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 depict Thalattosuchia nested within Neosuchia and the strength and character evidence supporting this position is discussed. Additionally, several characters traditionally postulated as dependent with the longirostrine morphology are critically examined upon 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.