On the enigmatic eusuchian Dolichochampsa minima: is the first cretaceous gavialoid from Gondwana?

PAULA BONA; JUAN ALEJANDRO ESCOBAR; MARTÍN DANIEL EZCURRA; FRANCISCO BARRIOS; ZULMA GASPARINI

Puerto Madryn

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2018

Asociación Paleontológica Argentina

Fossil crocodylomorphs have been outstandingly diverse worldwide, but Mesozoic members of Eusuchia are mostly restricted to a bunch of Laurasian Cretaceous species, with only a few occurrences in the Cretaceous of Africa (e.g., Aegyptosuchidae, Ocepesuchus). The only putative record of a South American eusuchian is the enigmatic Dolichochampsa minima from the uppermost Cretaceous Yacoraite (northern Argentina) and El Molino Formations (southern Bolivia). This species has been originally interpreted as a eusuchian because it presents posteriorly placed choana and procoelous vertebrae. However, Dolichochampsa have been rarely mentioned in discussion about the early evolutionary history of Eusuchia. Thus, we revisited the anatomy and analyze the phylogenetic relationships of this taxon based on the holotype (dentary: MLP 73-II-28-16) and referred cranial specimens (premaxilla, maxilla, braincase). Dolichochampsa minima is a valid species characterized by an extremely low snout and lower jaw, huge incisive foramen, dentary symphysis restricted to the first four alveoli, choana completely enclosed by pterygoids and robust and vertical basal tubera. It was recovered as a gavialoid crocodylian in two independent cladistics analyses as a result of multiple apomorphies: dorsally projected naris, maxilla with festooned lateral edge and equally-sized alveoli, straight dentary between fourth and tenth alveoli, maxillary and dentary teeth occluding in line, basioccipital without median crest, and basisphenoid with smooth depression posterior to the median Eustachian foramen. Dolichochampsa represents the first evidence of a Cretaceous crocodylian in South America, offering key information about the early history of Gondwanan eusuchians.