Oldest associated notoungulate skeleton from South America.

CARRILLO, J.; CARLINI A. A.; LORENTE, M.; CIANCIO MR; GELFO, J.; GOIN, F; ASHER, RJ

Berlin

Congreso; 74th Annual Meeting of the Society of Vertebrate Paleontology.; 2014

SVP

While fossil remains of endemic South American mammals are abundant in the SouthAmerican Paleogene, relatively complete and associated remains of a single individualare extremely rare. Previous estimates of isotemnid anatomy have been based on multipleindividuals, species, and/or genera to infer diversity in this cladistically basalnotoungulate group. Here, we report the discovery of a single individual ofThomashuxleya externa (Isotemnidae) from the Vacan subage of the CasamayoranSALMA (likely within the Lutetian Stage and close to the Bridgerian NALMA in age),from Cañadón Vaca, a locality east of Lago Colhué Huapi in Chubut Province,Argentina. Parts of nearly all elements of the skeleton are represented, including theskull, jaws, vertebrae, fore- and hind limbs, shoulder and pelvic girdles, and pes.Associated skeletal remains of other individuals, found at the same locality, include apartial articulated manus and contribute additional cranial material with which variationin Thomashuxleya can be assessed. Data from our single individual skeleton areconsistent with recent reconstructions of forelimb and pedal anatomy in Thomashuxleya,in particular regarding the previously uncertain association of an astragalus with otherskeletal elements. The associated astragalus is consistent with a plantigrade posturewithout significant running adaptations and lacks a cotylar fossa. Forelimb anatomy iscongruent with an erect posture for Thomashuxleya, as opposed to a crouching postureinferred for other Vacan isotemnids. This discovery provides an unusually completeanatomical basis for further studies of the long-ambiguous phylogenetic position ofendemic South American Mammals.