Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America

Abstract

Hypotheses of feeding behaviors and community structure are testable with rare direct evidence of trophic interactions in the fossil record (e.g., bite marks). We present evidence of four predation, scavenging, and/or interspecific fighting events involving two large paracrocodylomorphs (='rauisuchians') from the Upper Triassic Chinle Formation (∼220-210 Ma). The larger femur preserves a rare history of interactions with multiple actors prior to and after death of this ∼8-9-m individual. A large embedded tooth crown and punctures, all of which display reaction tissue formed through healing, record evidence of a failed attack on this individual. The second paracrocodylomorph femur exhibits four unhealed bite marks, indicating the animal either did not survive the attack or was scavenged soon after death. The combination of character states observed (e.g., morphology of the embedded tooth, 'D'-shaped punctures, evidence of bicarination of the marking teeth, spacing of potentially serial marks) indicates that large phytosaurs were actors in both cases. Our analysis of these specimens demonstrates phytosaurs targeted large paracrocodylomorphs in these Late Triassic ecosystems. Previous distinctions between 'aquatic' and 'terrestrial' Late Triassic trophic structures were overly simplistic and built upon mistaken paleoecological assumptions; we show they were intimately connected at the highest trophic levels. Our data also support that size cannot be the sole factor in determining trophic status. Furthermore, these marks provide an opportunity to start exploring the seemingly unbalanced terrestrial ecosystems from the Late Triassic of North America, in which large carnivores far outnumber herbivores in terms of both abundance and diversity.

A Short-Snouted, Middle Triassic Phytosaur and its Implications for the Morphological Evolution and Biogeography of Phytosauria

“…Furthermore, the premaxilla-maxilla suture is interdigitated, in contrast to the much looser connection between these elements in most other archosauriforms. All these features appeared early in the evolution of Phytosauria prior to the splitting of the Diandongosuchus lineage from other phytosaurs, recalling the trend observed in crocodyliform evolution42 of later rostrum elongation and dorsal expression of the external nares, as well as increases in body mass and changes in orientation of the temporal musculature, potentially serving to increase bite force and prey capture in a near-shore predator3743.…”

Early crocodylomorph increases top tier predator diversity during rise of dinosaurs

“…These ecological factors were taken from the published literature. We followed multiple authors in considering taxa of the following clades to represent the diversity of carnivorous, terrestrial, Triassic pseudosuchians: loricatans (Rauisuchidae + Crocodylomorpha) 6 10 , gracilisuchids 7 , poposauroids 50 , & ornithosuchids 9 ; and in assigning early theropods to this guild 5 . Dietary inferences for some Triassic pseudosuchians are ambiguous (e.g., Effigia 51 ); however, without quantitative analyses testing analogous ecomorphological traits in these taxa 45 47 , we include them as carnivores in keeping with the apparent dominant trophic habit of their clade, considering this a conservative approach.…”

“…Currently known diversity places Carnufex and Redondavenator as the largest, terrestrial carnivores within their respective assemblages 11 , which generally denotes apex predator status 30 . However, given the potential of sampling biases (e.g., no rauishuchids recovered from the Pekin Formation) and the nuances of extant predator interaction 6 30 , we refrain from restricting these taxa to apex predator roles. Rather, we adopt a more conservative approach that allows for incomplete sampling of large-bodied carnivores, by considering Carnufex and Redondavenator to be minimally, components of top-tier predator guilds within Triassic faunas.…”

“…The composition of modern ecosystems can be traced to the dynamic recovery of life in the aftermath of the catastrophic end-Permian mass extinction 1 . During the Triassic Period, unstable biotic communities 2 and morphing ecospace 3 gave rise to extant vertebrate clades such as frogs, lizards, mammals, turtles, and dinosaurs 1 4 5 and spurred seemingly unbalanced trophic assemblages dominated by an excess of predatory taxa 6 . In the Middle Triassic, terrestrial predator assemblages included the small-bodied mesopredators Gracilisuchidae 7 and top tier predator guilds dominated by poposauroids and basal loricatans (“rauisuchians”) 8 .…”

Osteology of Carnufex carolinensis (Archosauria: Psuedosuchia) from the Pekin Formation of North Carolina and Its Implications for Early Crocodylomorph Evolution

“…If correctly interpreted as a top terrestrial predator in the Pekin assemblage, Carnufex marks a rare and early instance of crocodylomorphs as top tier predators, a role more typically filled by other large basal archosaurs and later filled by theropod dinosaurs [ 69 , 70 ]. Indeed, ecosystems seem to have been in a state of flux for much of the Triassic, with an abundance of diverse predators available to fill vacated top predator roles [ 71 – 73 ]. Carnivorous pseudosuchians were significantly morphologically disparate at this time, and a variety of them were able to successfully invade top predator niches [ 1 , 7 , 74 ].…”