A reassessment of Nemolestes (Mammalia, Metatheria): Systematics and evolutionary implications for Sparassodonta

RANGEL, C.C.; CARNEIRO, L.M.; TEJEDOR, M.F.; BERGQVIST, L.P.; OLIVEIRA, E.V.

JOURNAL OF MAMMALIAN EVOLUTION

SPRINGER

Lugar: Berlin; Año: 2023

1064-7554

Nemolestes and Procladosictis are Eocene sparassodonts of controversial affinities. Nevertheless, despite the poor preservationof their holotypes, several other specimens have been tentatively assigned to these genera, as exemplified by someisolated teeth from the Itaboraí and Laguna Fría faunas. Here, we revise specimens referred to Nemolestes and Procladosictisfrom Itaboraí, Laguna Fría and Ameghino’s collection. Nemolestes differs from Patene in its more reduced metaconid, and“carnassialized” m4 (with reduced talonid and talonid cuspids, except the hypoconulid), features that make it possible to identifyspecimens from Itaboraí and Laguna Fría as Nemolestes. This taxon occurred from the early Eocene (Itaboraian SALMA)to the middle Eocene (Casamayoran SALMA). Nemolestes represents the oldest known hypercarnivorous sparassodont. Theinclusion of Nemolestes and Procladosictis in a comprehensive phylogenetic analysis recovered them in a polytomy as thesister taxa of Borhyaenoidea and a new unnamed clade that includes Lycopsis, Dukecynus, Hathliacynidae, Hondadelphysand Stylocynus. Nemolestes shares with these taxa, but not Patene, the presence of a “carnassialized” m4. Nemolestes differsfrom known borhyaenoids in the absence of a medially positioned protoconid and short anterolabial cingulid. Therefore,Nemolestes is an early lineage of Sparassodonta. “Procladosictis erecta” is a lower premolar of the unnamed clade, as itshows symmetric walls and a small precingulid. "Procladosictis erecta" should be, in fact, referred to Procladosictis. Ourphylogenetic analysis indicates that during the early middle Eocene (Laguna Fría and La Barda faunas), the unnamed cladeand Borhyaenoidea had already diverged. Therefore, the evolutionary history of these groups is older than previously thought.