Meeting Abstract
The fossil record rarely preserves direct evidence of ecology (e.g., gut contents), but it does preserve many cases of convergent morphology, which suggests similar ecologies. A beak, which is an edentulous dietary modification present in vertebrates and invertebrates convergently evolves repeatedly throughout the Phanerozoic. Here, we focus on the earliest evolution of beaks in the reptile fossil record during the Triassic Period (252 – 201.5 million years ago). We divide Triassic beaks into three morphotypes: 1) triangular, beak tapers to a point anteriorly, thin lateral walls, sharp occlusally; 2) square, a beak squared off anteriorly, thin lateral walls; 3) predentary, triangular beak, rounded lateral walls, concave midline shelf. With this subdivision, we analyze the phylogenetic distribution of Triassic beaks and a unique fossil beak (PVSJ 427) from the Ischigualasto Formation, San Juan, Argentina. PVSJ 427 is a small hematite-encased fossil that is triangular with a concave midline shelf, rounded lateral walls, and an anterior point. No bone is currently recognizable on the surface of PVSJ 427, indicating that it could be a natural cast of a beak or it could be a rhamphotheca encased in hematite. The rounded walls and midline shelf most closely matches the predentary morphotype, which is restricted to ornithischian dinosaurs, though this specimen is ~3 times larger than the earliest known Jurassic ornithischian beak. Regardless of phylogenetic position, PVSJ 427 reflects the earliest-known evolution of the predentary-like morphotype in vertebrates and indicates that this animal was likely exploring similar feeding ecologies to later-known ornithischian dinosaurs.
