Phlyogenetic relationships of basal mesoeucrocodylians: new clues to old conflicts

POL, D.

Denver, Colorado, EEUU

Congreso; 59th Meeting of the Society of Vertebrate Paleontology; 1999

Society of Vertebrate Paleontology

Mesoeucrocodylia, the largest crocodyliform clade, is composed of eusuchian crocodiles and a large paraphyletic assemblage of taxa previously called ‘Mesosuchia’.  Basal members of Mesoeucrocodylia show great morphological disparity, including herbivorous, carnivorous, and omnivorous forms.Within traditional taxonomic studies, several groups of these basal mesoeucrocodylian taxa were recognized (e.g., Notosuchia, Sebecosuchia, Atoposauridae).  Notosuchians draw the attention of several researchers because of the presence of several plesiomorphic character states in conjuction with a large amount of autapomorphies.  Current phylogenetic hypotheses depict different relationships between these basal forms and exhibit a conflictive character state distribution pattern. Attempting to address this problem, a phylogenetic analysis was performed involving 211 characters scored for 32 crocodyliform terminal taxa.  The two most parsimonious trees, found with implicit character weighting implemented in PIWE, differ from published evidence on phylogenetic relationships of basal mesoeucrocodylians in one major point: notosuchian monophyly.     Notosuchia was erected in the early seventies as a group of South American terrestrial Cretaceous crocodyliforms, but its monophyly was rejected in current cladistic approaches to crocodyliform phylogeny.  New evidence, from the cranium and the often overlooked postcranium, suggests that these crocodyliforms indeed belong to a monophyletic clade.  Notosuchians share several derived characters, such as the presence of postzygapophyseal laminae on dorsal vertebrae, neurovascular foramina on the lateral surface of the maxilla, dorsal osteoderms lacking anterolateral processes, and an anterolateral facing edge of the postorbital. The analysis also included Baurusuchus within this clade, in contrast with previous hypotheses.  This South American form has all the notosuchian synapomorphies that can be scored and additionally shares several derived characters that define its position nested well within Notosuchia.