Relationships and Implications of a New Didolodontidae (Mammalia) from the early Paleogene of Laguna Umayo, Perú.

GELFO J. N.; SIGÉ, B.

Neuquén

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

In the present work we preliminarily analyze a new ungulate from one of lowest pellet levels (LU-3 local fauna) of the Muñani Formation red mudstone unit outcrops at Laguna Umayo, southern Perú (Sigé et al., 2004). Besides various lower vertebrates, the LU-3 local fauna comprises an assemblage of peradectid and didelphimorphian marsupials plus the Notoungulata Perutherium altiplanense. The specimen (LU3-801) is a right m3, with a minimum size of 5.4 mm mesio-labially and 8.95 mm labio-lingually. The tooth is partially broken on the lingual side of the trigonid and distally to the hypoconulid. The crown is low and has bunodont cusps. The enamel seems to be creased over the talonid due to the presence of very small nodes. The metaconid is the highest cusp followed by a low and rounded protoconid. The paraconid is small, placed mesiolabially in respect to the metaconid. The distal wall of the trigonid is vertical, in contrast to the distal slope of the trigonid in Mioclaenidae Kollpaniinae. The hypoconid is the largest cusp of the talonid, from which the cristid obliqua runs first mesially then bends lingually but without contacting the trigonid. The trajectory of the cristid obliqua is comparable to that of Simoclaenus sylvaticus. The hypoconulid is centrally placed and connected to the large and bulbous entoconid by the postcristid. As in the didolodontid Raulcaccia peligrensis the postcristid is low and associated with two supplementary cusps, the first one placed lingual to the base of the hypoconulid, and the other distal to the entoconid. LU3-801 clearly differs from others South American Paleogene bunodont ungulates. It could be distinguished from all the primitive Mioclaenidae Kollpaniinae, found at the Tiupampa early Paleocene locality, Bolivia, because of its greater size, distally expanded talonid, much broader talonid basin and well developed talonid cusps and cristids. In contrast to the Litopterna Protolipterna ellipsodontoides from Itaborai, Brazil, the paraconid is still present, the distal outline of the talonid is not V-shaped but U-shaped, the entoconid is not close to the hypoconulid and the cristid obliqua bends lingually without contacting the protocristid. In comparizon to known Didolodontidae, LU3-801 is more closely related to the Peligran (middle Paleocene) Raulcaccia peligrensis, whereas it differs from those from the Eocene of Patagonia such as Didolodus multicuspis or Ernestokokenia nitida because of the position and size of the paraconid, usually absent, and the location of the main talonid cusps. In sum, LU3-801 is more derived than the early Paleocene Kollpaniinae, but less than the Eocene (Lutetian – Bartonian) patagonian didolodontids. Based on this, some biochronologic inferences are added as regards the age of the Laguna Umayo LU-3 local fauna. As previously suggested for this exposed part of the Muñani Formation (Sigé et al. 2004),  these inferences sustain: (1) either a middle Paleocene (Selandian) age like the Peligran SALMA, or (2) a late Paleocene – early Eocene (Thanetian – Ypresian) age, while they disfavor a latest Cretaceous – earliest Paleocene age.