EVOLUTION PATTERNS AND MORPHOLOGICAL DISPARITY ON SAUROPODOMORPHA DURING TRIASSIC-JURASSIC BOUNDARY

APALDETTI, CECILIA; POL, DIEGO; MARTÍNEZ, RICARDO N.

Los Angeles

Encuentro; Meeting of the Society of Vertebrate Paleontology; 2013

Sauropodomorpha was a diverse and abundant group of herbivorous dinosaurs that dominated most continental ecosystems of the Mesozoic era. The sauropodomorph fossil record reveals the Late Triassic- Early Jurassic was a key period of time in the evolution and diversification of this group, including the origin of Sauropoda. Here we present a morphological disparity study to evaluate the regions of the morphospace occupied by Sauropodomorpha from the Late Triassic to the Early Jurassic. Morphological disparity was approximated using multivariate analyses applied to different versions of a recently published phylogenetic matrix, in which the taxon and character sampling was altered in different ways. The results show the most basal and oldest sauropodomorphs (Carnian) forming a group that occupies a small and well-differentiated region of the morphospace. During the Norian this group diversified notably both taxonomically and ecologically, which is reflected in that they occupy a different and much broader region of the morphospace. The boundaries of this region of the morphospace are mostly determined by robust basal sauropodomorphs from the Southern Hemispheres. During the Lower Jurassic the region of the morphospace occupied by Sauropodomorpha is markedly expanded with respect to that of the Norian. This is expanded toward two news regions where some of the most conspicuous sauropodomorphs of that period are positioned: the gracile forms known as massospondylids and the derived and giant forms of basal sauropods. This result evidences that the increase in taxonomic diversity was paralleled by a rise in the morphological disparity of Sauropodomorpha during the Late Triassic. After the Triassic-Jurassic boundary the disparity increases notably, but the taxonomic diversity is not altered significantly. These marked steps in the changes and expansions of the morphospace regions occupied by basal sauropodomorphs is to a large degree dominated by the signal coming form taxa known from the southern hemisphere.