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

BONA, P.; ESCOBAR, J.A.; EZCURRA, M. D.; BARRIOS, F.; GASPARINI, Z.

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina, Puerto Madryn, 2018; 2018

Fossil crocodylomorphs have been outstandingly diverse worldwide, but Mesozoic members of Eusuchia are mostly restricted to a bunch ofLaurasian Cretaceous species, with only a few occurrences in the Cretaceous of Africa (e.g., Aegyptosuchidae, Ocepesuchus). The onlyputative record of a South American eusuchian is the enigmatic Dolichochampsa minima from the uppermost Cretaceous Yacoraite (northernArgentina) and El Molino Formations (southern Bolivia). This species has been originally interpreted as a eusuchian because it presents posteriorlyplaced choana and procoelous vertebrae. However, Dolichochampsa have been rarely mentioned in discussion about the early evolutionaryhistory 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 byan extremely low snout and lower jaw, huge incisive foramen, dentary symphysis restricted to the first four alveoli, choana completely enclosedby pterygoids and robust and vertical basal tubera. It was recovered as a gavialoid crocodylian in two independent cladistics analyses as a result ofmultiple apomorphies: dorsally projected naris, maxilla with festooned lateral edge and equally-sized alveoli, straight dentary between fourth andtenth alveoli, maxillary and dentary teeth occluding in line, basioccipital without median crest, and basisphenoid with smooth depression posteriorto the median Eustachian foramen. Dolichochampsa represents the first evidence of a Cretaceous crocodylian in South America, offering keyinformation about the early history of Gondwanan eusuchians.