Phylogenetic relationships of south american aetosaurs (Archosauria: Crurotarsi)

DESOJO, J. B.; BÁEZ, A. M.

Rio de Janeiro, Brasil

Congreso; II Congreso Latino-Americano de Paleontología de Vertebrados; 2005

Museo Nacional/UFRJ

The armoured aetosaurs are known from Late Triassic continental rocks of all continents, except Australia and Antarctica. In South America aetosaurs are represented by Aetosauroides Casamiquela from Brazil and Argentina, Chilenosuchus Casamiquela from Chile, and Neoaetosauroides Bonaparte from Argentina. Unfortunately, only the latter taxon was included in most recent phylogenetic analyses because the aetosaurian nature of Chilenosuchus was denied and Aetosauroides was considered a junior synonym of Stagonolepis Agassiz, a genus of the northern hemisphere. A revision of the South American materials rejected both hypotheses and a parsimony analysis including the three taxa was performed in an attempt to better understand their relationships within Aetosauria. A matrix of 17 taxa, including Chanaresuchus, Saurosuchus, and Sphenosuchus as outgroup taxa, and 39 characters, of which 8 are new, was analyzed in PAUP 4.0b for MacIntosh. An exact search (Branch and Bound) produced 3 shortest trees 83 steps long, CI=0.63, and RI=0.71. The strict consensus tree obtained with the data set is (Chanaresuchus, (((Aetosauroides, ((Aetosaurus, S. robertsoni), ((Neoaetosauroides, Coahomasuchus), (S. wellesi, ((Longosuchus, Lucasuchus), (((Chilenosuchus, Redondasuchus, Typothorax) Paratypothorax), (Acaenosuchus, Desmatosuchus))))))), (Saurosuchus, Sphenosuchus)). The genus Stagonolepis was found to be paraphyletic and Aetosauroides the sister taxon of the remaining aetosaurs. The results also suggest that South American taxa do not form a monophyletic group; this implies a moderate biotic interchange between both hemispheres in the early and middle Carnian.