Foot posture of Colbertia magellanica (Mammalia, Notoungulata) from São José de Itaboraí Basin (Upper Paleocene), Rio de Janeiro

Abstract

FOOT POSTURE OF COLBERTIA MAGELLANICA (MAMMALIA. NOTOUNGULATA) FROM SAO JOSE DE ITABORAI BASIN (UPPER PALEOCENE), RIO DE JANEIRO. Colbertia magellanica is one of the most common species of the Itaborai Basin, upper Paleocene of Rio de Janeiro State. Some Studies demonstrated that it is possible to determine the resting foot posture of a fossil mammal as plantigrade or digitigrade employing measurements of extant mammals and statistical analysis. Following this methodology, 11 measurements were taken from six metatarsals III. 22 astragali and 22 calcanea of C. magellanica. Principal Components Analysis and Discriminat Function Analysis were performed. The Principal Components Analysis was not Successful in separating plantigrade and digitigrades forms, but the Discriminat Function Analysis classified 92,5%, of known cases correctly and C. magellanica as a plantigrade mammal. Colbertia magellanica tarsal morphology was compared with Protolipterna ellipsodontoides. a litoptern from Itaborai Basin with digitigrades foot Posture. The main differences are: (i) the astragalus of P. ellipsodontoides has a deep astragalar trochlea while in C. magellanica the trochlea is wide and shallow; (ii) in the calcanecum of P. ellipsodontoides the portion anterior to astragalar facets is longer than in C. magellanica. but the shaft is longer in this species; and (iii) metatarsal III is proportionately longer in P. ellipsodontoides. The locomotor habit of C. magellanica call not be confidently suggested based solely on the analyzed bones.