Depicting the evolutionary history of Xenungulata (Mammalia)

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

Mendoza

Congreso; 4th International Paleontological Congress; 2014

International Palaeontological Association

he South American native ungulates were very diverse and include at least five extinct orders; in two of these orders, all members have low-crowned cheek teeth and a bilophodont pattern: Pyrotheria (middle Eocene-late Oligocene) and Xenungulata (late Paleocene-early Eocene). Xenungulates were neither so diverse nor abundant as Notoungulata, Litopterna or even Astrapotheria. Their cheek teeth show an exclusive specialization comparable to extant Tapiridae (Perissodactyla), and their ecological niche was probably very different than that of other South American ungulates. Only the families Etayoidae and Carodniidae are recognized among xenungulates, and their relationships remain uncertain and need further discussion. Etayoidae are represented by Etayoa bacatensis from the late Paleocene of Colombia and Notoetayoa gargantuai from middle Paleocene of Patagonia, Argentina. Both are known from fragmentary jaws. E. bacatensis has an alveolus of a large and procumbent canine and a long diastema mesial to the p2, suggesting the absence of p1. Thesefeatures, not present in Carodniidae, resemble the morphology of Trigonostylopidae Astrapotheria, but in contrast to them, the symphysis in E. bacatensis is not fused. Carodniidae include Carodnia feruglioi and a gen. et. sp. nov., both from the middle Paleocene, Patagonia and Carodnia vierai from the early Eocene of Itaboraí, Brazil. The afore mentioned new taxon from the lower levels of Cerro Redondo presents a primitive pattern with remnants of the trigonid structure mesial to the protolophid (metacristid and paracristid), a well-marked cristid obliqua and the development of a short entocristid. These characters agree with an older age of the bearing levels with respect to those of the classic ?Carodnia Zone.? Other new specimens found in Patagonian outcrops of the Peñas Coloradas Formation indicate the presence of two jaw morphologies for remains that couldbe assigned prima facie to C. feruglioi. One is characterized by its robustness and the height of the mandibular body below the m3, whereas the other type has a more slender and gracile jaw. These morphological differences could be interpreted as sexual dimorphism, but there is no dental evidence to corroborate that the morphotypes belong to the same species. Summarizing, the monophyly of Xenungulata is here questioned on the basis of the exposed arguments.