Brief disscussion of Henricosborniidae (Mammalia, Notoungulata) dental characters and their possible implication

BAUZA, NICOLAS; GELFO J.N.; LOPEZ G. M.

Congreso; VI Congreso Latinoamericano de Paleontología de Vertebrados; 2018

Henricosborniids are a group of South American native ungulates mainly found in Brazil(São José de Itaboraí) and Argentina (Mendoza, Jujuy and several Patagonian localities)and are suspected to be also present in the early Paleocene of Bolivia (Tiupampa). Thefamily used to be part of the most basal notoungulate suborder, Notioprogonia, togetherwith the Arctostylopidae and Notostylopidae. More recently, most authors have agreedthat arctostylopids should be excluded from notoungulates and argued in favor of theparaphyly of notioprogonians; henricosborniids and notostylopids have been regarded asprimitive groups and given little attention. Henricosborniidae includes the generaHenricosbornia, Peripantostylops, Othnielmarshia and Simpsonotus, although other taxaare commonly associated, like Paginula and Itaboraitherium. Acamana is a highly dubiousspecimen originally described as a Notoungulata indet. but later associated withSimpsonotus. Due to its fragmentary record, principally consisting of isolated teeth, thegroup is not very useful beyond dental characters; consequently, it has not been taken intoconsideration in most phylogenetic analysis, or only few taxa have been included (i.e.Henricosbornia, Simpsonotus). Even though there is consensus about the basal position ofthe group within the order, the family is recovered as polyphyletic or, more commonly,paraphyletic. The study of specimens from the early Eocene of Las Violetas, Paso delSapo, and Las Flores, the oldest known Patagonian localities where notoungulates havebeen found, allows preliminary aspects of the dental morphology of Henricosborniidae tobe discussed. Here we recognize the following characters, shared by the mentioned taxa:1) ectoloph with well-marked paracone and metacone columns; 2) crochet present, obliqueto the ectoloph, with variable development; 3) third upper molar triangular in its shape,with poorly developed hypocone; 4) reduced trigonid with very short paralophid; 5)entoconid more like an isolated cusp and not completely crested. These features seem toshow a retention of primitive characters for the family, contrasting with other Eocenegroups present in the same temporal and geographic distribution. In contrast tohenricosborniids, notostylopids present an ectoloph with only a paracone column and astrong crochet. Primitive typotheres (e.g. Oldfieldthomasiidae, Archaeopithecidae,Interatheriidae) also have a distinct metacone column in the ectoloph but differ fromhenricosborniids in having a complex crown pattern that suggests the presence of acrochet. The triangular shape of the third upper molar seems to be unique toHenricosborniidae but can also be considered as a primitive state for notoungulates, sincethe scarce hypocone development is a feature also present in Arctostylopidae as well asother Paleocene taxa. Although the configuration mentioned above is highly informativefor henricosborniid identification, these characters need to be evaluated in a phylogeneticcontext in order to determinate if they are good for defining Henricosborniidae as anatural group.