CONICET | Buscador de Institutos y Recursos Humanos

Two individuals assigned to Carodnia feruglioi were found in the basal levels of the Río Chico Group, Bajo de La Palangana locality, Chubut Province, Argentina. The specimens (Museo Paleontológico Egidio Feruglio) correspond to two partially preserved skulls and isolated dental elements, associated with Crocodylia bones. All were recovered in a flat area of approximately 1,000 m2, 34 m above sea. The fossil matrix consists of gray to greenish clays, with ochre, red and chestnut mottling. These levels of red sandstones, originally mentioned by Simpson as the Carodnia Faunal zone were identified in the Peñas Coloradas Formation (Danian), but recently interpreted as the basal section of Las Flores Formation. These remains recovered in situ make it possible to identify the level defined by Simpson in their type locality and enable a more detailed definition of the lithostratigraphic unit. Paleovegetational context inferred from phytoliths in the sediment suggests dominantly forest elements with extremely rare or no evidence of grasses from Peñas Coloradas up to the upper part of Las Flores Formation. However, whereas the sample from Peñas Coloradas consists largely of palm phytoliths, the samples closer to the Carodnia level, and from Las Flores, contain a highly diverse set of phytoliths from primarily woody angiosperms, with only relatively rare palm morphotypes. This suggests either a shift from more palm-dominated habitats to mixed, angiosperm-dominated forests, or spatial heterogeneity in this region during the Paleocene?early Eocene. The cranial elements were found mainly within the sediment, with the outcropping portions presenting a high degree of erosion at the bone level, and with several exposed teeth broken or with fresh fractures. Preliminary results from the preparedspecimens provide, for the first time, new details of the dental morphology of Carodnia feruglioi. The right M3 has a long, thick, and very low mesial cingulum close to the neck of the tooth. The protoloph is the highest structure, slightly concave distally, and with a clear facet of mesial wear along its entire length. It corresponds to the longest labiolingual section ofthe tooth and joins together the para- and protocone. The protocone is the most voluminous cusp and occupies the entire lingual side of the tooth. There is no true lingual cingulum, but a very faint crenulation is present at the base of the protocone, joining the precingulum and the postcingulum. The paracone is smaller than the protocone but larger than the metacone, which is located more lingually than the paracone, generating the distal transverse shortening of the last uppermolar. A short lophid is projected from the apex of the metacone to a weak metaconule (?) and from there, the lophid continues at an angle of 90° towards a low and short postcingulum, which runs from the distolingual face of the protocone to the distolabial side of the metacone. The qualitative differences with the M3 of Carodnia vierai are greater than in the caseof other, more conservative loci, suggesting the presence valuable phylogenetic characters.

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