A geometric morphometric approach to the analysis of skull shape in Triassic dicynodonts (Therapsida, Anomodontia) from South America

ORDOÑEZ, MARIA DE LOS ANGELES; CASSINI, G.; VIZCAINO, SERGIO; MARSICANO, CLAUDIA

JOURNAL OF MORPHOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Lugar: New York; Año: 2019

0362-2525

Dicynodont therapsids were a major component of the Permo-Triassic terrestrial 27 ecosystems across Pangea and have been regarded as specialized herbivores. In South 28 America, the group is well represented by several taxa of the clade Kannemeyeriiformes 29 spanning from the Middle to the Late Triassic. 30In order to evaluate if cranial differences among taxa are potentially related to 31 differences in feeding function, we performed a geometric morphometric analysis on 28 32 South American dicynodont crania. We digitized 19 cranial landmarks and conducted 33 generalized Procrustes analysis, principal components analysis (PCA), principal 34 components analysis between groups (bg-PCA), and a branch weighted squared-change 35 parsimony approach. Phylogenetic inertia was not a significant driver of cranial shape 36 evolution in the group, whereas PCA and bg-PCA support that major morphological 37 changes are concentrated in the preorbital region (relative length of the snout and width 38 of the caniniform process), in the position of quadrate condyle in relation to the 39 caniniform process, and in the increase in the intertemporal surface area. In this context, 40 tusked Dinodontosaurus, ?Kannemeyeria? and Vinceria have relatively smaller 41 adductor attachment areas and input moment arm than younger taxa lacking tusks, such 42 as Ischigualastia, Stahleckeria and Jachaleria. Differences in cranial morphology in 43 later dicynodonts reflect modification in feeding mechanics, probably due to changes in 44 food resources (vegetation) in their habitats towards the end of the Triassic.