Functional morphology of the Triassic apex predator Saurosuchus galilei (Pseudosuchia: Loricata) and convergence with a post-Triassic theropod dinosaur

Assessing the adductor musculature and jaw mechanics of Proterochampsa nodosa (Archosauriformes: Proterochampsidae) through finite element analysis

Proterochampsids are a group of South American nonarchosaurian archosauromorphs whose general morphology has been historically likened to that of the extant Crocodylia, which purportedly exhibited similar habits by convergence. Taxa from the genus Proterochampsa, for example, show platyrostral skulls with dorsally faced orbits and external nares and elongated snouts that might indicate a feeding habit similar to that of crocodilians. Nonetheless, some aspects of their craniomandibular anatomy are distinct. Proterochampsa has comparatively larger skull temporal fenestrae, and a unique morphology of the mandibular adductor chamber, with a remarkably large surangular shelf and a fainter retroarticular region in the mandible. In light of this, we conducted biomechanical tests on a 3-dimensional model of Proterochampsa nodosa including the first Finite Element Analysis for proterochampsians and compared it with models of the extant crocodylians Tomistoma schlegelii and Alligator mississippiensis. Our analyses suggested that, despite the differences in adductor chamber, Proterochampsa was able to perform bite forces comparable to those modeled for Alligator and significantly higher than Tomistoma. However, the morphology of the surangular shelf and the adductor chamber of Proterochampsa renders it more prone to accumulate stresses resulting from muscle contraction, when compared with both analogs. The elongated lower jaw of Proterochampsa, like that of Tomistoma, is more susceptible to bending, when compared with Alligator. As a result, we suggest that Proterochampsa might employ anteriorly directed bites only when handling small and soft-bodied prey. In addition, Proterochampsa exemplifies the diversity of arrangements that the adductor musculature adopted in different diverging archosauromorph groups.

Paleoneurology and neuroanatomical notes on the South American "rauisuchian" Saurosuchus galilei from the Ischigualasto formation, San Juan, Argentina

Non-crocodylomorph loricatans, traditionally known as "rauisuchians," are considered as the top predators of the Triassic continental faunas that reigned before the emergence of the well-known theropod dinosaurs. In particular, Saurosuchus galilei is a large quadrupedal prestosuchid loricatan found in the Ischigualasto Formation from northwestern Argentina. Here, we reevaluated the braincase of S. galilei and present the first paleoneurological study based on the partial natural casts of the holotype and the digital cranial endocast of the referred specimen PVSJ 32. The braincase of S. galilei was here reinterpreted, identifying the sutures of the supraoccipital, otoccipital, basioccipital, parabasisphenoid, prootic, and laterosphenoid. A unique feature identified in the braincase of S. galilei is the presence of deep paracondylar recesses associated with pharyngotympanic pneumaticity, which has not been identified in any other "rauisuchians" so far. Most of the structures of the encephalon were recognized in the cranial endocast and natural casts including cranial nerves V-XII, olfactory bulbs, main blood vessels and sinuses, and inner ear. These structures allowed us to quantify some of its sensorial capacities and recognize that S. galilei had an enhanced olfactory acuity, with coefficients higher than those expected for its body size, a condition previously observed in living crocodilians and tyrannosaurid dinosaurs. An improved sense of smell might have allowed Saurosuchus to track its prey from long distances and compensate for the poorer development of its other senses like vision and balance.