A New Carodnia-like Xenungulata (Mammalia) from the Paleogene from Patagonia, Argentina.

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

Neuquen, Argentina

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

The Xenungulata are only known for scarce taxa from the Paleogene of several South American localities, as Patagonia (Carodnia feruglioi and Notoetayoa gargantuai), the brazilian locality of Itaboraí (Carodnia vierai) and Colombia (Etayoa bacatensis). An unpublished taxa from Rio Loro Formation apparently also indicate their presence at Northwestern Argentina. We preliminary describe a fragmentary right lower jaw with the partially preserved p4 and m1 nearly complete (MLP 90-II-12-121).  This remain came from Cerro Redondo, at the East of the Chubut Province and was collected from the lower fossil horizon identified by Simpson (1935) and considered as probably stratigraphically equivalent or older than the “Carodnia Zone”, despite no common taxa were found between them. The m1 is well preserved, with the trigonid somewhat higher, wider and longer than the talonid. This tooth shows an almost labio-lingually oriented bilophodont structure characteristic of other Xenungulata and Pyrotheria. The protolohid is mesially concave, the cutting plane of the lophid is parallel to the one of the hypolophid, and both are inclined distally. There is no trace of the paraconid. The metaconid could be distinguished from the protolophid by a strong enamel edge that bends at the lingual tip of the lophid. The protoconid is not so clearly distinguished from their outline. A short metacristid descend mesio-labially from the metaconid almost reaching the lingual end of the paracristid. The paracristid abruptly descends mesio-lingually from the labial ends of the protolophid, and progressively bends lingually, to the mesial base of the trigonid. In the hypoconid sector of the hypolophid, a smooth cristid obliqua descends up to the base of the distal wall of the trigonid near to the protoconid area. The entoconid could be identified in the hypolophid by an enlargement at its lingual end. The new taxa here described differ from Etayoidae due to the absence of paraconid and a more bilophodont tooth, being  morphologically close to Carodniidae. But, in contrast to Carodnia, the new specimen presents a more 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 generalized characters seem to highlight Simpson (1935) observation that Cerro Redondo lower level could be older than ‘Carodnia Zone’ at Bajo de La Palangana.