Morphology and function of the jaw joint of traversodontids (Therapsida-Eucynodontia)

CARLOS AGUSTÍN SCANFERLA

Buenos Aires

Simposio; International Symposium on Mesozoic Terrestrial Ecosystems; 1999

Studies on the jaw articulation of cynodonts constitutes a fertile field for phylogenctic and functional interpretations. Among cynodonts, traversodontids exhibit a highly derived condition in both the quadrate and the articular bone of the jaw: in contrast with the uniform morphology present in most non-mammalian cynodonts, in which the quadrate trochlea forms a hemicylindcr transversely oriented in traversodontids the trochlea has a wide, almost flat, articular surface, and its lateral condyle is anteroposteriorly expanded. Correspondingly, the articular bone of the traversodontid jaw has a shallow glenoid cavity. The quadrate and articular morphologies described above offer new information on the masticatory mechanism in traversodontids. This information is congruent with the previously inferred ectental and palinal movements, based on dental morphology. Notably, the articular surfaces involved in the traversodontid jaw joint resembles the convex squamosal glenoid cavity and dentary condyle present in extant ungulates (e.g., Lama, Capra), which have ectental and propalinal movement. Moreover, traversodontids exhibit mechanisms of mandibular contention (e.g., canines- paracanin fossae complex, transversal crests on molariforms, lateral trochlear condyle of the quadrate) that are concordant with such masticatory movements. Remarkably, wide mandibular movements could not be present in all traversodontids, because certain members of the group (e.g., Pascualgnathus. Rusconiodon) posses hypcrtrophied canines, that would had limited transversal and anteroposterior jaw movements.