Produced by the Population Genetics and Evolution class, Furman University

The Triassic: Marasuchas and the Ornithodirans
Ornithodira is a subsection of the Archosauromorphs clade that contains the superorders Dinosauromorpha and Pterosauromorpha. The defining features are an upright gait and an S-curved neck, although the pterosauromorphs had neither of these; they are nonetheless included because of Ornithodira’s definition as being the last common ancestor of the dinosaurs and pterosaurs. The latter of these are possibly the very first flying vertebrates, although it is the former that is considered the progenitor of modern birds (Gauthier 1986). Marasuchus lilloensis, formerly Lagosuchus lilloensis, is a single species in a genus created to differentiate between different forelimb proportions of fossils. Both genera are the most likely ancestors of the dinosaurs. Originally discovered in Argentina, M. lilloensis measures approximately 40 cm in length. The morphology of its spine suggests bipedal locomotion, a horizontal back, and an arched neck, and the long tibiae and metatarsals may be adaptive to aid in running (Sereno and Arcucci 1994).

Page by Will Towler
Artist’s rendering of Marasuchus. Available from: blogspot.com

Gauthier J. 1986. Saurischian monophyly and the origin of birds. Memoirs California Academy of Sciences 8:1-55.

Sereno PC, Arcucci AB. 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. Journal of Vertebrate Paleontology 14:53-73.