On the Occurrence of a Nemolestes (Metatheria, Sparassodonta) in the Guabirotuba Formation (Curitiba Basin), Middle Eocene, Southern Brazil

Nemolestes is a poorly known Eocene sparassodont, as it is known only by very fragmentary, isolated, and damaged fragments of lower molars. This fragmentary condition restricts comparisons with other sparassodonts. Here, the specimen MCN.P.1326 is presented, an isolated trigonid of a right m1, from the Guabirotuba Formation, Curitiba Basin, middle Eocene of Southern Brazil. This tooth has a metaconid and paraconid subequal in size, a condition only observed for the m1 of early lineages of sparassodonts. Its size is proportionally larger than most of Eocene early taxa, ruling out associations with most of them. Its width by length ratio (RW/L) lower than 0.70 and talonid by trigonid length proportions (RLtal/Ltri) suggests its association with Nemolestes. Its inclusion in the concept of a phylogenetic analysis recovered it as an early sparassodont. When assigned to Nemolestes, this taxon is recovered as the sister taxon of Chlorocyon, Borhyaenoidea and the unnamed clade A. The presence of Nemolestes in the Guabirotuba local fauna extends the paleogeographic range of this genus to Southern Brazil and supports the middle Eocene dating for this unit.