Persistence of a lineage of Gondwanan mammals in Mid-Paleogene levels of western Patagonia

TEJEDOR, M.F.; GOIN, F.J.; CHORNOGUBSKY, L.; LOPEZ, G.; GELFO, J.N.; BOND, M.; WOODBURNE, M.O.; GUROVICH, Y.; REGUERO, M.A.

San Juan, Argentina

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Museo de Ciencias Naturales, San Juan

Recently, Tejedor et al. (2009) described a new Paleogene mammalian fauna from levels of the Volcanic-Pyroclastic Complex of the Middle Chubut River. All specimens were exhumated from two localities in the vicinity of Paso del Sapo (Chubut Province, Argentina). The specimens described here (LIEB-PV 2000 and LIEB-PV 2001) come from the locality known as La Barda (“26 de Mayo” Farm), with an estimated age ranging between 47-45 Ma (middle Eocene; early Lutetian). They consist of two, probably upper molariform teeth referable to the same taxon of Gondwanatheria (Mammalia, ?Allotheria). The Gondwanatheria include two families: first, the Sudamericidae Scillato-Yané and Pascual, 1985, of hypsodont dentitions, that have been recorded from the Late Cretaceous of Patagonia, Madagascar, India, and possibly Africa, as well as from the medial Paleocene of Patagonia and the Eocene of Antarctica. Second, the more generalized, brachydont Ferugliotheriidae Bonaparte, 1986, which are only known from the Late Cretaceous of Patagonia (Los Alamitos, La Colonia, and Cerro Tortuga localities). The new molariform specimens are characterized by: (1) size larger than other Gondwanatheria; (2) molariforms are probably protohypsodont, comparable to the earliest Sudamericidae; (3) there are strong transversal crests that alternate with labial furrows; (4) each tooth has a single root, very short and rounded; (5) the teeth are strongly worn at their occlusal surfaces, and the labial edge is less worn than the lingual one. The protohypsodont aspect of the teeth, as well as the strong, transverse crests, suggest affinities with the Sudamericidae; on the other hand, the occlusal pattern performed by the crests and furrows shows more similarities with the Ferugliotheriidae. If the allocation of the new taxon to this latter family is confirmed, this would extend its biochron approximately 20 Ma, up to the middle Eocene. The new finding agrees with the known distribution of other gondwanatherians in the southernmost portion of South America (but see Goin et al., 2004). Therefore, it needs to be confirmed if the distribution of this group in South America included other (Neotropical) areas of this continent or, to the contrary, if it was an endemic radiation of the Andean Region (Patagonian Subregion) of the Austral Kingdom.