The Taxonomic Status of Notocaiman stromeri (Crocodylia, Alligatoroidea) and the Early Diversity of South American Caimanines

Abstract

The early diversification of caimanines is one of the least understood aspects of the evolutionary history of Crocodylia. The Palaeogene Argentinian caimanine record is extremely relevant because it provides key information on the early history of the clade. Most of the Palaeocene South American species are only or mainly known from partial lower jaws. Among the oldest Argentinian caimanines, Notocaiman stromeri (middle Palaeocene, Las Violetas Formation, Chubut Province) and Eocaiman palaeocenicus (lower Palaeocene, Salamanca Formation, Chubut Province) are represented by a partial left dentary and a fairly complete lower jaw, respectively. Notocaiman stromeri, has been phylogenetically interpreted from an alligatorid closely related to Eocaiman to an indeterminate eusuchian, but a modern anatomical revision of this species is lacking. Here, we redescribe in detail the only known specimen of Notocaiman stromeri (PVL 752) to revise its taxonomy and phylogenetic relationships. We concluded that Notocaiman and Notocaiman stromeri are nomina dubia and we refer PVL 752 to Eocaiman cf. E. palaeocenicus. Our phylogenetic analysis found Eocaiman palaeocenicus as the sister taxon to the Eocaiman cavernensis + Eocaiman itaboraiensis clade. Thus, here we reduce the alpha taxonomic diversity of alligatorids in the Palaeogene of South America but reinforce a geographically broad diversification of the genus Eocaiman, from the Palaeocene to the Eocene/Miocene in this continent.