A Snapshot of Late Triassic Field Work in Southern Utah

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.

A 200 million year old Eubrontes track from the St. George Dinosaur Discovery Site.

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.

An artist’s rendition of a late Triassic environment, featuring phytosaurs. Art credit to Julie Crowell.

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.

A phytosaur skeleton at the New Mexico Museum of Natural History and Science.

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.

Three paleontologists excavating a phytosaur skull. Notice how tight the quarry is, the woman’s knees are resting on the plaster jacket that contains the skull.
Four men carefully transporting the phytosaur skull down the debris slope below the quarry.

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.

An up-to-date image of the phytosaur skull from above.
The same image but with features shown for emphasis. The two elongate holes are the nose and the two holes to the right of the nose are the eyes.

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.

A photo of the volunteer that has done the bulk of the preparation on this skull, Jim Williams.

Southern Parkway Fossils

Many people travel along the Southern Parkway from I-15 exit 2 along to Hurricane. Travelers pass by new housing developments, the St. George Airport, and Sand Hollow Reservoir. The knowledgeable traveler might be aware of fossil sites in Warner Valley when they pass that exit. However, many are completely unaware of fossil sites beneath the road itself. These sites, known as the Southern Parkway Project (SPP) were discovered in 2011 during surveys conducted before the road’s construction. Our Curator, Andrew Milner, was the lead investigator for this project and discovered many fossil localities in the area including plants, dinosaur and other tracks, and teeth.

One of the prominent fossil-bearing rock formations along the Southern Parkway (SR-7) is called the Kayenta Formation (~190-195 million years old). It represents one of the red rock geologic units that southwestern Utah is famous for. This Early Jurassic formation was deposited by river systems that flowed across flat terrain in a very arid environment. Even though the climate was extreme, plants and animals flourished. 

Two men breaking apart rocks looking for fossils.
Fred Overkamp (SGDS volunteer, left) and Andrew Milner (SGDS paleontologist, right) excavating the Ws538 locality in March 2013.

Two important sites were discovered in 2011 and excavated prior to, and during construction of the Southern Parkway. One of these localities, called Ws538, is very unique because it preserved fossils rarely seen in the Kayenta Formation. It produced hundreds of well-preserved plant fossils, including cycads, ferns, horsetails, and conifers. Additionally, fossil teeth from a variety of animals were discovered such as large and small meat-eating dinosaurs, plant-eating dinosaurs (Scelidosaurus-like), three kinds of crocodylians, fishes, and a possible flying reptile and synapsid. Many of these teeth are too small to easily see without a microscope, and were discovered upon closer inspection of plant samples from this site. These teeth are all on the scale of a few millimeters but their perfect preservation is enough to identify different animals and different tooth types. A variety of dinosaur tracks such as Eubrontes, Grallator, Kayentapus, and Anomoepus were also found, along with swim traces of fishes, and meating-eating and plant-eating dinosaurs. 

A plant-eating dinosaur tooth on the scale of millimeters.
Ornithischian tooth (plant-eating dinosaur) similar to those of Scelidosaurus. Scale = 1 mm.

The second locality, called the Hamblin Tracksite, produced more than 600 footprints. It is by far the richest occurrence of Anomoepus tracks (produced by plant-eating dinosaurs) known from western North America. This site also preserved a running trackway made by a large theropod dinosaur. This tracksite was mapped and photographed in detail, and many fossils were collected and/or replicated. 

People on a hillside cleaning a fossilized track surface with a mountain in the background.
SGDS team excavating the Hamblin Tracksite in September 2011.

Hundreds of specimens were collected from both of these sites and are now housed at the St. George Dinosaur Discovery Site (SGDS) and the Natural History Museum of Utah (UMNH). Today, the Southern Parkway (SR-7) rests on top of these fossil localities, and the majority of these sites were removed for highway construction. Some examples of the amazing fossils from this area are currently on display in the lobby at the SGDS until January 2025, come and see it!

Some Anomoepus tracks from the Hamblin Tracksite. Many of these specimens are now in collections at UMNH, however SGDS has replicas of some in their collections.