INVESTIGADORES
EZCURRA Martin Daniel
congresos y reuniones científicas
Título:
The evolutionary radiation of Triassic dinosauriforms
Autor/es:
NOVAS, F.E.; EZCURRA, M. D.
Lugar:
Puerto Madryn
Reunión:
Encuentro; Reunión Anual de Comunicaciones de la Asociación Paleontologica Argentina; 2005
Institución organizadora:
CENPAT
Resumen:
Until recently, sister taxa of Dinosauria were restricted to Ladinian forms (e.g., Lagerpeton, Marasuchus, Pseudolagosuchus), thus evolution of Dinosauriformes depicted a step-wise pattern in which the dinosaurian diversification occurred after the appearance of non-dinosaurian dinosauriforms, without recording a temporal overlapping between them. However, recent discoveries and re-study of previously known dinosauriforms allow to change the understanding of the early evolution of Dinosauriformes. Discovery of the gracile archosaur Silesaurus opolensis (Late Carnian, Poland) demonstrates that non-dinosaurian Dinosauriformes survived into the Late Triassic, being co-eval with the oldest known dinosaurs (e.g., herrerasaurids, Eoraptor, Saturnalia). Moreover, Silesaurus exhibits notable cranial and dental apomorphies (e.g., leaf-shaped teeth, beaked-jaw), suggesting that an important, hidden morphological disparity among basal dinosauriforms remains to be discovered. In the same line of evidence is the systematic reassessment of Eucoelophysisbaldwini (Early Norian, United States), originally thought as a coelophysoid theropod. Contrarily to this interpretation, Eucoelophysis lacks neotheropod and dinosaurian features (e.g., femoral head strongly inturned, ligament sulcus on femoral head, fibular crest on proximal tibia) indicating that Eucoelophysis is not a theropod dinosaur but a basal dinosauriform. This means that non-dinosaurian dinosauriforms survived into the Norian. In this regard, the currently available fossil record shows that non-dinosaurian dinosauriforms and herrerasaurids (e.g., Chindesaurus) survived into the early Norian, thus tends to blur the impact of the Carnian-Norian extinction event, as far as for dinosauriforms is regarded. In sum, a better understanding of early dinosauriform diversification emerges from recent discoveries and re-studies, which show that the early evolutionary radiation of dinosauriforms was more complex than it was thought. In fact, the numerical dominance of dinosaurs at the end of the Triassic (Norian) was preceded by an stage (Carnian-early Norian, at least) in which non-dinosaurian dinosauriforms co-habited with the flourishing basal saurischian forms.