While phytosaur fossils are not found at the St. George Dinosaur Discovery Site (SGDS), they represent a unique time in geological history that eventually gave way to the rise of dinosaur-dominated fossil sites such as SGDS. Researching phytosaurs provides important context to Earth’s history before an event that would set the stage for life in the Early Jurassic.
The Triassic-Jurassic boundary is defined by a mass extinction event that occurred around 201 million years ago. The dinosaur tracks at SGDS are from the Jurassic side of this boundary. To understand what happened during this mass extinction event, paleontologists need to study the animals that came both before and after.
The Triassic period (252 to 201 million years ago) began in the wake of the end-Permian mass extinction, the most devastating extinction event in Earth’s history. Many ecological niches were left empty by this extinction, and Triassic life had a lot of room to grow. New groups of plants and animals diversified rapidly to fill these spaces. By the end of the Triassic, a variety of marine and flying reptiles, early dinosaurs, and crocodile-like archosaurs–including phytosaurs–had emerged and proliferated all over the world.
However, as the Triassic came to a close, the planet underwent a dramatic shift. Much like the extinction event that began the Triassic, the end-Triassic extinction event led to the loss of a significant portion of Earth’s species. The causes of this mass extinction are complex and debated, but most geological evidence points to volcanic activity and associated climate change as major drivers. The massive release of greenhouse gases like carbon dioxide likely led to global warming, ocean acidification, and disrupted ecosystems. Many groups of organisms died off as a consequence, including the phytosaurs which had become one of the dominant reptiles of the Triassic.
Phytosaurs were large, crocodile-like reptiles that roamed the land and waters during the Late Triassic. Despite their resemblance to modern crocodiles, phytosaurs are not closely related to them. Phytosaurs branched off of a group called Archosauria, which also includes dinosaurs and the ancestors of modern crocodiles on different branches. They were primarily semi-aquatic creatures, with long, slender bodies, sharp teeth, and long, crocodile-like snouts useful for hunting fish and other small prey. Their long tails enabled them to navigate through water with ease, and their eyes were positioned atop their heads, allowing them to keep a watchful eye on their surroundings while remaining mostly submerged. Despite their success, the phytosaurs did not survive the mass extinction at the Triassic-Jurassic boundary. The extinction of phytosaurs and other groups of animals paved the way for the dominance of dinosaurs during the Jurassic and Cretaceous periods.
In March 2020, paleontologists were enjoying an early field season and discovered a Late Triassic phytosaur skull south of Moab, Utah. In 2022, after two return trips, the SGDS field crew finally managed to collect this skull in a large plaster jacket and bring it back to SGDS for preparation. It took five days with three people constantly digging with hand tools, hammers, chisels, crow bars, and a rock saw to fully excavate this skull. This block weighed about 300 pounds and took the strength of four men to transport down a rocky slope. It took about an hour and a half to get the skull from the quarry down to a pick up truck for transport to St. George, Utah.
Since 2022, volunteers have spent hundreds of hours preparing this phytosaur skull. Today, many elements are now recognizable. Fossils like the phytosaur skull provide invaluable insight into life during this transitional time. These fossils not only help us understand the physical characteristics and lifestyles of these ancient creatures but also offer a glimpse into the changes that shaped the evolution of life on Earth. This important fossil is being prepared in the lab window at SGDS. If you have not seen it yet, come see the amazing progress being made.
As scientists continue to explore and uncover new fossils from this critical time in Earth’s history, we learn more about the resilience of life in the face of mass extinctions. We can see the lasting impact of those events on the biodiversity we see in the fossil record and today. The discovery of this phytosaur skull is another piece in the puzzle of life’s long history on Earth, and a reminder that life has evolved and adapted through countless changes in the planet’s history.
