Body mass estimation in Triassic Cynognathia (Therapsida, Cynodontia) from South America based on 3d craniomandibular landmarks

Abstract

Body size is one of the main proxies for understanding the biological aspects of fossil vertebrates. Body masses of five species of Cynognathia were obtained from 3D configurations of cranial and mandibular landmarks from 29 specimens. Equations based on centroid size from the literature of ungulates and calculated from carnivorous mammal database were used. In addition, the maximum size per species was obtained by geometric similarity and compared with estimates based on postcranial elements from recent literature. The values of body mass obtained from the centroid size do not present major discrepancies with those obtained from the postcranium, except in the larger specimens of Massetognathus and Exaeretodon. Geometric similarity is useful as a comparative method and for detecting over- or underestimates. Larger size ranges than previously reported were recorded for each cynognathian species. Among the small species, Andescynodon ranged from 1 to 6.5 kg and Pascualgnathus, 2.5 to 6 kg; medium-sized Massetognathus, 10 to 30 kg; and the large species, Cynognathus ranged 100 to 150 kg and Exaeretodon, 100 to 280 kg. The relationship between diet and body mass observed in extant mammals was used as a comparison to determine the possible ecological niche of cynognathians.