Notoungulata: Henricosborniidae da “Fenda 1968”, Paleógeno da Bacia de Itaboraí, Estado do Rio de Janeiro: estudo taxonômico dos elementos dentários

Abstract

A new basal notoungulate is described here. This is represented by maxillary and dental fragments, and by isolated teeth. The holotype and referred material were recovered from the “1968 Fissure” of the Itaboraí Basin, Rio de Janeiro State, Brazil. This basin, of Itaboraian age, has been regarded as early Eocene in recent contributions. The generalized appearance and brachydont dentition of the studied specimens, together with the presence of some typical traits (poorly developed entolophid, well-developed metacone column, etc.) indicate that it represents a Gen. et sp. nov. of Henricosborniidae. It is distinct from all other henricosborniids by a combination of characters, such as the presence of a long crochet, the development of two small cristae at the ectoloph, the large accessory trigonid cusp, among others. It is also easily distinguishable from typotherians by the absence of crista 1 and from toxodontians by the absence of crista intermedia. The phylogenetic analysis including all henricosbornid genera does not allow us to reach solid conclusions about the relationship of the new taxon with the other members of this group. It did not present conclusive evidence for the synonymy between Itaboraitherium atavum and Othnielmarshia pristina, previously suggested. Moreover, the reference of these forms as henricosborniids, based on the complex occlusal dental pattern observed in both cases, is questioned. Finally, based on the observations made in the present study, we consider that the accessory trigonid cuspid, referred in some contributions as a paraconid, may be associated with some cusps located mesially to the metaconid and identified as pseudoparaconids in past studies.