Abstract
Triassic predatory guild evolution reflects a period of ecological flux spurred by the catastrophic end-Permian mass extinction and terminating with the global ecological dominance of dinosaurs in the early Jurassic. In responding to this dynamic ecospace, terrestrial predator diversity attained new levels, prompting unique trophic webs with a seeming overabundance of carnivorous taxa and the evolution of entirely new predatory clades. Key among these was Crocodylomorpha, the largest living reptiles and only one of two archosaurian lineages that survive to the present day. In contrast to their existing role as top, semi-aquatic predators, the earliest crocodylomorphs were generally small-bodied, terrestrial faunivores, occupying subsidiary (meso) predator roles. Here we describe Carnufex carolinensis a new, unexpectedly large-bodied taxon with a slender and ornamented skull from the Carnian Pekin Formation (~231 Ma), representing one of the oldest and earliest diverging crocodylomorphs described to date. Carnufex bridges a problematic gap in the early evolution of pseudosuchians by spanning key transitions in bauplan evolution and body mass near the origin of Crocodylomorpha. With a skull length of >50 cm, the new taxon documents a rare instance of crocodylomorphs ascending to top-tier predator guilds in the equatorial regions of Pangea prior to the dominance of dinosaurs.
Highlights
Crocodylomorph increases top tier predator diversity during rise of dinosaurs Lindsay E
Carnufex and Redondavenator expand the diversity of top tier terrestrial predator guilds in the Late Triassic to at least five distinct archosaur clades and document vast overlap in body size between contemporary dinosaurs and crocodylomorphs (Fig. 2b)
The Triassic-Jurassic transition marks a shift to dichotomous body mass distributions between terrestrial members of these two clades, and a loss of top tier crocodylomorph diversity after the end-Triassic extinction (ETE) (Fig. 2b)
Summary
The maxilla of Carnufex is transitional in possessing a straplike, elongate ascending process at least 2/3rds the length of the antorbital fenestra. This is an intermediate condition between the. Craniocaudally reduced ascending process of other early diverging crocodylomorphs (e.g., Dromicosuchus[14], Sphenosuchus16), and the relatively elongate, yet caudally expanded, ascending process of rauisuchids (e.g., Polonosuchus[17]). A well-defined, rugose lateral ridge on the jugal process of the maxilla rises sharply to terminate at the ventral margin of the rostral antorbital fenestra (Fig. 1c), a condition otherwise undocumented in loricatans. The descending process of the lacrimal widens rostrocaudally to contact the expanded rostral process of the jugal near the ventral orbital margin (Fig. 1a) as in crocodylomorphs. An ectepicondylar groove and a supinator process are present, as in aetosaurs, other loricatans, yet in contrast to other crocodylomorphs
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