New Proterochampsid Specimens Expand the Morphological Diversity of the Rhadinosuchines of the Chañares Formation (Lower Carnian, Northwestern Argentina)

EZCURRA, MARTÍN D.; VON BACZKO, M. BELÉN; TROTTEYN, M. JIMENA; DESOJO, JULIA B.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Año: 2019 vol. 56 p. 79 - 115

0002-7014

The proterochampsids are crocodile-like, small- to medium-sized, quadrupedal and predatory stem-archosaurs. The rhadinosuchinesare a clade of deeply nested proterochampsids that are the most abundant diapsids of the Massetognathus-Chanaresuchus Assemblage Zoneof the Chañares Formation (lower Carnian) of north-western Argentina. Here, we describe two new rhadinosuchine proterochampsid specimensrecently collected from the Massetognathus-Chanaresuchus Assemblage Zone of the Chañares Formation. These specimens are represented byan articulated partial skeleton and disarticulated cranial and postcranial bones, respectively. One of them is less complete, but its well-preserveddisarticulated bones considerably expand the anatomical knowledge of certain regions of the rhadinosuchine skeleton. The combination ofcharacter-states present in both specimens and shared with other known rhadinosuchine species (e.g., Chanaresuchus bonapartei, Gualosuchusreigi, Rhadinosuchus gracilis) results in an unexpected increase of the morphological diversity of the group (e.g., antorbital fossa on the horizontalprocess of maxilla, well-exposed antorbital fossa on lacrimal, X-shaped osteoderms). We conclude that the taxonomy of the currently knownrhadinosuchine specimens should be revisited, including a careful reappraisal of the intraspecific variation and the post-mortem deformationthat affected the specimens in different ways.