INVESTIGADORES
LECUONA Agustina
congresos y reuniones científicas
Título:
New anatomical information of the suchian Gracilisuchus brings new insights on the phylogeny of basal crocodylomorphs
Autor/es:
LECUONA, A.
Lugar:
Neuquén
Reunión:
Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008
Institución organizadora:
Universidad Nacional del Comahue
Resumen:
Gracilisuchus stipanicicorum is a small suchian archosaur considered as related to different lineages of archosaurs by various authors in the past (Romer, 1972; Bonaparte, 1975; Benton and Clark, 1988; Sereno, 1991), although recently other authors allied this taxon as closely related to Crocodylomorpha (Parrish, 1993; Juul, 1994; Clark et al., 2004). Despite its importance for understanding the origin of the latter clade, the anatomical knowledge on Gracilisuchus is poor and has not been significantly revised since its original description (Romer, 1972). A re-study of its hind limb morphology was carried out, adding 48 new phylogenetically informative characters. In order to evaluate the impact of these new characters in the early evolution of Crocodylomorpha, as well as, test more thoroughly the affinities of Gracilisuchus, the new characters were added to a recent cladistic analysis of Crocodylomorpha (Clark et al., 2004). Additionally, five suchian archosaurs were added to the dataset, comprising aetosaurs and rauisuchians. Ten most parsimonious trees were obtained in the cladistic analysis providing different topological results from the original analysis and showing Gracilisuchus in two alternative positions. One of these depict it as the closest sister taxon to Crocodylomorpha (supported by a brevis shelf on ventral margin of postacetabular ilium), being more derived than the clade composed of Erpetosuchus and Postosuchus. The alternative topology shows Erpetosuchus, Postosuchus and Gracilisuchus as successive sister taxa of Crocodylomorpha. The new characters added provide a better resolution of the large basal polytomy of Crocodylomporpha present in the original analysis (Clark et al., 2004), allowing the recognition of a clade comprising Kayentasuchus and Hesperosuchus (sharing the presence of lesser trochanter on femur), which is depicted as the sister group of (Dromicosuchus + (Sphenosuchus + more derived crocodylomorphs)). Furthermore, those trees in which Gracilisuchus is the sister taxon of Crocodylomorpha, have a unique resolution for basal crocodylomorphs, whereas when Gracilisuchus is depicted in the alternative position, three alternative resolutions of the base of Crocodylomorpha are found as equally parsimonious. This shows that determining the most closely related crocodylomorph sister taxa, has a large impact on the resolution of the basal relationships of Crocodylomorpha.