Ptychotherates

MEANING: Fold hunter

PERIOD: Late Triassic

CONTINENT: North America

Ptychotherates is a basal saurischian that lived during the alate Triassic period in what is now North America.

Abstract from paper: The most complete record of the earliest dinosaur lineages is from the Carnian from the higher latitudes of Pangea (e.g. present-day Brazil, Argentina), but dinosaurian assemblages from the upper stages of the Upper Triassic are better known from the low latitudes of Pangea (present day southwestern USA). How early carnivorous dinosaurian diversity matches or mismatches at various latitudes remains to be documented because of uncertainty around the spatio-temporal ranges and phylogenetic relationships of early dinosaur lineages. We examine low-latitude diversity patterns through the lens of the saurischian dinosaur Tawa hallae and close relatives, including a new species, Ptychotherates bucculentus gen. et sp. nov. The new taxon is known from an incomplete but well-preserved skull (CM 31368) from the uppermost Triassic Coelophysis Quarry in northern New Mexico. The new taxon clearly shares synapomorphies with Tawa hallae, such as distinctive fossae on the quadrate and otoccipital and a dorsoventrally tall and laterally flat jugal. However, the new taxon is distinguishable from all other coeval ornithodirans by a combination of many character states, including the proportionally dorsoventrally deepest jugal known for any Triassic-aged dinosaur. Higher-palaeolatitude ecosystems across Pangea show a complete turnover of carnivorous dinosaurs by neotheropods in the Norian and Rhaetian, but the ‘Chindesaurus–Tawa’ clade (Morphoraptora clade nov.) coexisted with neotheropods possibly until the End-Triassic Extinction Event. This suggests a low-latitude ‘museum’ where early-diverging lineages survived much longer than at higher latitudes, and that the End-Triassic Extinction Event affected dinosaur diversity more than previously hypothesized.

Ptychotherates is from the Late Triassic. The Triassic is the first geologic period of the Mesozoic, spanning from the end of the Permian Period 252 million years ago to the beginning of the Jurassic 201 million years ago. Both the start and end of the Triassic were marked by major extinction events. In the aftermath of the devastating Permian-Triassic extinction, life gradually rebounded, giving rise to new groups that would shape the Mesozoic Era. The global climate during the Triassic was mostly hot and dry, with vast deserts dominating the interior of the supercontinent Pangea. Over time, as Pangea began to rift apart, the climate slowly became more humid, creating new environments and opportunities for ecological diversification.

For much of the Triassic, dinosaurs were not yet the dominant terrestrial animals. Instead, the land was populated by a variety of other reptiles, including sprawling archosaurs. Early synapsids, the lineage that would eventually lead to mammals, were also still present but declining. Vegetation was dominated by drought-tolerant plants such as seed ferns, cycads, ginkgoes, and early conifers. These hardy plants formed the base of recovering ecosystems during this volatile time.

It wasn't until the Late Triassic, around 230 million years ago, that the first true dinosaurs appeared. Early forms were small, bipedal, and lightly built, likely preying on insects and small vertebrates. While they remained minor players compared to other reptilian groups, their agility, upright stance, and efficient breathing gave them advantages that would prove crucial in the long run. As the Triassic drew to a close, another mass extinction event reshaped life on Earth once again, wiping out many of the dominant reptile groups and clearing the way for dinosaurs to rise to prominence in the Jurassic.

Tawa is a basal saurischian. Saurischia is one of the two major clades of dinosaurs, sister to the ornithischia. It includes two of the theropods, which gave rise to birds, and the sauropodomorphs, which include the long-necked giants. Saurischians are united by a number of anatomical traits, most notably their “lizard-hipped” pelvic structure, where the pubis points forward. Early members of the group were generally small to medium-sized, lightly built animals, often bipedal, with grasping hands and relatively long hind limbs. Their teeth and skull shapes varied, reflecting a range of diets from carnivory to omnivory, and their overall body plans represent the foundation from which some of the most extreme dinosaur forms would later evolve.

Basal saurischians, representing the early stages of this lineage before the clear split into theropods and sauropodomorphs, are primarily known from the Late Triassic. These animals tend to exhibit a mosaic of traits that would later become more specialized in their descendants. They were typically bipedal, with relatively simple, lightly constructed skeletons and generalized limb proportions. Some show features associated with predation, such as recurved teeth and grasping hands, while others hint at more omnivorous or herbivorous tendencies. This combination of characteristics has made their relationships difficult to resolve, and their exact placement within early dinosaur evolution remains an area of active research. Despite this uncertainty, basal saurischians provide critical insight into the early diversification of dinosaurs, capturing a transitional phase before the emergence of the distinct theropod and sauropodomorph body plans that would come to dominate the Mesozoic.