The forelimb of Cyonasua sp. (Procyonidae, Carnivora): substrate preference and locomotory mode inference

TARQUINI, JULIANA; TOLEDO, NÉSTOR; MORGAN, CECILIA CLARA; SOIBELZON, LEOPOLDO HÉCTOR

Mendoza

Congreso; 4th international palaeontological congress. the history of life: a view from the Southern Hemisphere; 2014

International Palaeontological Association-CONICET Mendoza

The family Procyonidae is represented in South America by two extinct genera: ?Cyonasua and ?Chapalmalania, and five extant ones: Bassaricyon, Nasuella, Potos, Procyon and Nasua. The living forms have adapted to a wide variety of arboreal and terrestrial habitats, preferably near water bodies. In this work we draw inferences about the substrate preference and locomotory mode of ?Cyonasua, being the first quantitative approach to this question. Twenty-two linear measurements from the forelimb stylopodium and zeugopodium were taken; for each individual, the raw values were divided by the geometric mean of all measurements to minimize the effect of size. The transformed values were analyzed by Principal Component Analysis (PCA) to explore variation. The sample included 11 taxa of Carnivora with different substrate preference and locomotory modes: tree-dwellers (Potos, Arctictis), semi-aquatic (Lontra), scansorial (Nasua, Eira), terrestrial-climbers (Procyon, Leopardus, Tremarctos), terrestrial-non-cursorial (Galictis, Conepatus), and terrestrial-cursorial (Lycalopex). The first two principal components (PC) summarized 42.8% of the total variation of the sample. PC-1 explained 23.7% of the variation; the taxa with semi-aquatic, terrestrial-cursorial and terrestrial-non cursorial habits occupied the positive extreme of this axis, associated to narrower ulnar diaphyses, elongated humeral heads and distally projected humeral trochleas. The tree-dwellers, scansorials and terrestrial-climbers, located on negative values of PC-1, showed wider ulnar diaphyses, shorter humeral heads, and less distally projected humeral trochleas. PC-2 explained 19.08% of the total variation; the semi-aquatic, tree-dwelling, scansorial and terrestrial-non cursorial taxa occupied the positive extreme, showing a wide distal humeral articular facet, well protruding entepicondyle and shorter ulna. Toward the negative values of PC-2, the terrestrial-limbers and terrestrial-cursorials presented longer ulnae, narrow distal humeral articular facet and less protruding entepicondyle. In this context, the location of ?Cyonasua sp. in the morphospace was unique, with near-zero values on PC-1 and negative values on PC-2, reflected in a relatively long ulna with somewhat narrow distal humeral articular surface, and entepicondyle slightly more protruding than in terrestrial-climbers and cursorials; this would be associated to greater development of hand flexor muscles, and elbow movements restricted to sagittal plane. Accordingly, in terms of the ecologic groups separated along PC-1, the forelimb of ?Cyonasua can be characterized as intermediate, while regarding PC-2 it was most similar to that of Procyon. Thus, for ?Cyonasua sp. we infer terrestrial habits with potential climbing abilities. In-progress studies about hind limb will provide additional information about substrate preference and locomotory mode.