Humeral distal epiphysis of Cyonasua sp. (Carnivora, Procyonidae) from the upper pliocene from Miramar , Argentina. A 2D Geomethric Morphometric study.

TARQUINI, JULIANA; MORGAN, CECILIA CARLA; SOIBELZON, LEOPOLDO HÉCTOR

Diamante, Entre Rios

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

The extinct procyonid Cyonasua is endemic to South America and its postcranial anatomy is poorly known. We analyzed the shape of the humeral distal epiphysis, an important component of the elbow joint involved in load transference and forelimb movement, to estimate the potential locomotory mode of Cyonasua sp. MLP 35-X-4-4. The sample included 120 specimens belonging to extant carnivorans (18 genera of 7 different families) spanning a wide ecological range, analyzed through 2D geometric morphometrics using eight landmarks and 28 semi-landmarks. Shape variation between genera was explored through principal component analysis (PCA). The first two PC summarized 62.3 % of shape variance. Changes along PC1 involved articular surface depth, entepicondyle development, and length of lateral supracondylar ridge. PC2 reflected mainly changes in trochlear depth, medial projection of entepicondyle and lateral extension of the supracondylar ridge. Extant procyonids tended to be clustered in the morphospace occupying positive values of PC1 (shallow articular surface, well-developed entepicondyle, relatively long lateral supracondylar ridge), and a wide range along PC2 (varied development of trochlea and supracondylar ridge), sharing the morphospace of other scansorial, arboreal and generalized carnivorans, and separated from cursorial and semiaquatic forms. Cyonasua presented negative scores on both PCs, reflecting its deeper distal articular surface and less developed entepicondyle. Thus, it did not share the morphospace of its living relatives but fell near the semi-fossorial mustelid Meles; it presented a relatively robust distal humerus and a deeper, potentially more stabilized elbow joint that suggests terrestrial habits with some digging abilities.