Dinosaur precursors and early dinosaurs from Argentina

EZCURRA, M. D.; MARTÍNEZ, R. N.

Contribuciones Científicas del Museo Argentino de Ciencias Naturales ?Bernardino Rivadavia?

Museo Argentino de Ciencias Naturales

Lugar: Capital Federal; Año: 2016 vol. 6 p. 97 - 107

Dinosaurs include two main branches, Ornithischia and Saurischia, with a minimum divergence time of approximately 231 Ma (late Carnian) based on the age of the oldest known members of the group. Argentinean non-dinosaurian dinosauromorphs are known from the Upper Triassic Chañares, Ischigualasto and Quebrada del Barro formations, including five or six nominal species and an unnamed form. The non-dinosaurian dinosauromorph assemblage of Chañares is the most diverse worldwide and has been crucial to understand the origin of the group. The Ischigualasto Formation preserves a formidable fossil record and has provided the most comprehensive source of information about the oldest known dinosaurs. Eight valid dinosaur species are known from this unit and represent the three principal dinosaurian subgroups-Ornithischia, Sauropodomorpha, and Theropoda. The anatomical knowledge or understanding of the evolution of character-states in some of these early dinosaurs (e.g. Pisanosaurus, Herrerasaurus) still prompts considerable debate about their phylogenetic position.