Paleontology in Petrified National Forest

Petrified Forest National Park is a remarkable place to learn about fossils and the science of paleontology, and much of what we know about Triassic vertebrate paleontology has been discovered, excavated, and researched at Petrified Forest. Petrified Forest has been a hotspot for Triassic fossils since it was first established as a national monument to protect “the mineralized remains of Mesozoic forests” in 1906. In fact, John Muir and Annie Alexander found some of the first fossils in what is now the park. Located in northeastern Arizona adjacent to the City of Holbrook and the Navajo Nation, Petrified Forest is a true ‘living laboratory’ for Triassic paleontologists from all over the world to come to do research in the park lands protected for preservation and enjoyment by researchers and visitors alike. For the last 20 years, Petrified Forest has been home to a modernized paleontology research program, led by National Park Service paleontologists and interns, including an active field program, archives and museum collections, state-of-the-art fossil preparation labs, and museum programs and exhibits.

Now that much of the 220,000-acre park has been inventoried for fossils, the Petrified Forest paleontology program is focusing more on hypothesis-driven research questions, asking less of “what animals and plants were here?” and more of “how did the plants and animals respond to changing climates during the Triassic Period?”.

Scientists, including park paleontologists and colleagues at partner institutions, are investigating these primary research questions in places such as the Smithsonian National Museum of Natural History, the Burke Museum of Natural History and Culture at the University of Washington, Yale Peabody Museum, and Virginia Tech.

The Triassic Period is often called the Dawn of the Dinosaurs because the earliest members of that evolutionary lineage, which went on to reign over terrestrial ecosystems for the next 150 million years, first appear in the fossil record in Triassic rocks in Europe, South America, southern Africa, and the southwestern United States. However, unlike the relatively diverse groups of meat-eating and long-necked dinosaurs on most of Pangea during the Triassic (for example, Herrerasaurus and Plateosaurus), those of the Triassic of what are now Arizona, Utah, New Mexico, and western Texas were small-bodied and minor members of their ecosystems, unlike other reptile groups more closely related to crocodylians than to birds that were far more common and ecologically important. Coelophysis is found in New Mexico (most notably Ghost Ranch) and Arizona and was a lithe, fast predator that likely lived in large packs. Chindesaurus is named from Petrified Forest and is also found in New Mexico. The Chindesaurus specimen nicknamed ‘Gertie’ was ceremoniously airlifted from the Painted Desert at Petrified Forest in 1985.

Was there an earlier extinction prior to the end-Triassic mass extinction?

The end-Triassic mass extinction is one of the ‘Big Five’ mass extinctions that shaped the evolution of Life on Earth over the last 500 million years. Around 201 million years ago, the end-Triassic extinction resulted in the loss of more than half of the global biodiversity and it was likely caused by volcanic eruptions during the opening of the northern Atlantic Ocean, much like a large zipper opening through the supercontinent Pangea. Petrified Forest preserves sedimentary rocks of the Chinle Formation that are 27 to 7 million years older than the end-Triassic extinction (228 to 208 million years old), and fossil vertebrates, plants, and invertebrates are found throughout the Chinle Formation at the park. A better understanding of the specific rock layers and how old they are (using uranium-lead age dating) discovered over the last 20 years has revealed an earlier potential extinction event at the park ~213 million years ago, with some animal groups found only above or below the rock layer correlating with that event. This has been hypothesized as being the result of a meteor impact in Quebec, Canada.

How do animal communities change over time as viewed through the fossil record?

Factors like where, how, and when an animal died, as well as what happened to it after death, all determine whether something becomes fossilized (to say nothing of being found and excavated by paleontologists), making the fossil record biased towards animals with hard parts (for example, a mollusk shell, shark tooth, or dinosaur bone). In the past, the fossil record at Petrified Forest has been biased towards large-bodied animals like phytosaurs or animals with extra bony pieces of armor along their backs, like aetosaurs. These were relatively easy to find and collect, and we know a lot about the ecology and anatomy of them because of the hard work by past researchers. However, with the advent of new technologies and by reinventing older ones, Petrified Forest paleontologists are leading the field in the study of microvertebrates: animals or parts of animals that are too small to be researched without a microscope. If a modern biologist was able to collect every animal from an acre of any given habitat, the vast majority of things would be small-bodied (think worms, insects, beetles, lizards, birds), and the same is true in the Triassic. Petrified Forest paleontologists are using a combination of screen-washing and CT scanning/3D printing techniques to better visualize the smallest components of Triassic animal communities through time and are learning how those communities responded to the changing climate during the Triassic.

Join Dr. Adam Marsh, lead paleontologist at Petrified Forest National Park, and investigate these questions and more during two events during the 2022 Flagstaff Festival of Science. Saturday, September 24 (2:00 pm) is a guided hike through paleontological sites in the Chinle Formation at Petrified Forest. Monday, September 26 (5:00 pm) is a talk on the Hidden Diversity of the Triassic Period at Petrified Forest at Lowell Observatory.

Adam is a member of the Board of Directors of the Flagstaff Festival of Science and a research associate at the Museum of Northern Arizona and the Vertebrate Paleontology Laboratory at the University of Texas at Austin. More information on paleontology at Petrified Forest can be found at https://www.nps.gov/pefo/learn/paleontology.htm, and a list of scientific publications on paleontology is provided at https://www.nps.gov/pefo/learn/published-research.htm.