The postcranial remains of Allalmeia atalaensis (Mammalia, Notoungulata) from the Divisadero Largo Formation, Mendoza, Argentina

LORENTE, M. ; GELFO J. N.; LOPEZ G. M.

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Museo de Ciencias Naturales Universidad Nacional de San Juan

We redescribe and interpret the postcranial remains of Allalmeia atalaensis Rusconi, 1946, found in Divisadero Largo Formation, Mendoza, Argentina. It is one of the few basal notoungulates found with dental and postcranial remains directly associated. The skull, several vertebras, and part of the apendicular skeleton were preliminarily described by Rusconi (1946) but later, most of these remains were lost. Recently, part of the holotype, composed by the distal parts of two humeri, a proximal portion of the right femur, several broken diafisis and most of the two feet (PV 507), was recovered and prepared. In contrast to the original description (Rusconi, 1946) in the right humerus the suprathroclear foramen is present, and the entepicondylar foramen absent, and only a smooth epicondylar fossa is present. Similar morphology is present in the distal humerus of Colbertia lumbrerensis Bond, 1981. Due to the preparation, some details of the plantar side of the feet are available for the first time: (1) The cuboid has a L-shape tuberosity with a marked groove for the peroneus longus ligament; (2) in the left foot, a sesamoid is present over the lateral cuneiform; (3) the navicular has an anterior W outline, with a lateral projecting rim. In addition, the feet are pentadactyl, being the metatarsal of the hallux less than half in length of the second metatarsal. The 3rd and 4th metatarsals are parallel, being the 4th metatarsal slightly larger than the 3rd. The intermediate phalanx of the 4th finger of the right foot has a prism like shape, with the proximal side wider than the distal one. This wider base articulates with the plantar side of the proximal phalanx. In an isolated proximal phalanx of the left foot, the articulation is also mostly plantar. So, the intermediate phalageal row is oblique to the proximal one. In contrast to most known notoungulates, this morphology is comparable to the one observed among extant felines, as for example, Leopardus geoffroyi d'Orbigny and Gervais, 1844, Leopardus colocolo Molina, 1782, and Panthera leo Linneo, 1758. These traits could suggest a similar posture and locomotion movements of the feet.