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A UT paleontologist is helping uncover a treasure trove of fossils from the age of dinosaurs in a seemingly unlikely place: the heart of the Dallas-Fort Worth metroplex.

Discovered in 2003 in Arlington, Texas, by amateur fossil hunters Art Sahlstein, Bill Walker, and Phil Kirchoff, the fossil site—now known as the Arlington Archosaur Site (AAS)—preserves a nearly complete ancient ecosystem ninety-five million to 100 million years old in an area undergoing rapid residential development.

A volunteer holding a piece of tibia (shin bone) from a Protohadros, a type duck-billed dinosaur.
A volunteer holding a piece of tibia (shin bone) from a Protohadros, a type duck-billed dinosaur.

While most of Texas was covered by a shallow sea at this time, the Dallas-Fort Worth area formed a large peninsula that jutted out into this sea, creating a lush environment of river deltas and swamps that teemed with wildlife, including dinosaurs, crocodiles, turtles, mammals, amphibians, fish, invertebrates, and plants. Many of the fossils found on the site represent species previously unknown to the world.

Stephanie Drumheller-Horton, an assistant adjunct professor in UT’s Department of Earth and Planetary Sciences, is a member of a team of paleontologists working to excavate and research the AAS. She is joined by Chris Noto, assistant professor of biology at the University of Wisconsin–Parkside; Thomas Adams, curator of paleontology and geology at the Witte Museum in San Antonio; and Anthony Fiorillo, chief curator of earth sciences and vice president of research and collections at the Perot Museum of Nature and Science in Dallas.

The team recently received a grant from the National Geographic Society to continue excavation and study of this unique fossil site. The funding will support excavation at the site through summer 2017. Teams of scientists and trained volunteers will work to recover as many fossils as possible before completion of a nearby residential development.

A typical dig, with a group of volunteers working on the fossil layer (dark layer) from summer 2015.
A typical dig, with a group of volunteers working on the fossil layer (dark layer) from summer 2015.

“These conservation efforts are important for supporting the ongoing work at the AAS, but the rapid pace of development in the area means the long-term future of the site and its fossil resources is less certain,” said Noto. “Therefore it is critical that we collect as many fossils and other data as possible now while continuing to demonstrate the scientific, educational, and cultural value of this site to the community.”

Adams said the site provides a unique look at dinosaur life.

“Research has traditionally been focused on either the Early or Late Cretaceous, which have proven to be incredibly fossil-rich,” said Adams, “But the diversity of fossils and the number of species being discovered at the AAS are providing a true picture of an ancient coastal ecosystem that existed ninety-five million years ago.”

The sponsored research will expand the group’s scientific study of the site, allowing new analyses of the rocks enclosing the fossils, including techniques such as palynology (the study of fossil pollen and spores), stable isotope, X-ray diffraction, and X-ray fluorescence, which will reveal important details about the ancient climate and environment that existed at this time during the Cretaceous Period.

Field work 2015 dino jacket - 1
Volunteers making a plaster jacket around a dinosaur bone during the summer 2015 dig.

Working with these fossils will help us understand how Texas fits into the larger picture of animal life change that was happening through the middle of the Cretaceous Period, around ninety million to 115 million years ago. Very little is known about this turnover in North America, and the AAS preserves one of the best fossil records for this time, providing a critical window into this important transitional period.

As the name suggests, archosaurs—the group that includes dinosaurs, birds, and crocodylians—are the most common fossils at the AAS. Bite marks and skeletal material from a large fossil crocodile indicate crocs were actually the top predators in the rivers and swamps of this part of Cretaceous Texas.

“We call the Mesozoic [a span of180 million years, divided into the Triassic, Jurassic, and Cretaceous periods] the Age of Dinosaurs for a reason,” said Drumheller-Horton, “But people sometimes forget that other kinds of animals lived in these environments too. Fossils from the Arlington Archosaur Site preserve evidence that the crocs were major predators in this ecosystem, even eating the dinosaurs that lived there.”

Plans are underway to perform detailed computed tomography scans on a selection of turtle and dinosaur fossils that exhibit pathologies such as injuries or infections, to better understand what formed these structures and what they can tell us about how the animals lived and died.

From its first discovery, the AAS has been an important tool for science education and outreach. Trained volunteers from the community, who are passionate about preserving this important resource, perform the majority of the fossil excavation. This is an unprecedented opportunity for the public to be involved in a scientific excavation, sharing their experiences directly with the community.

Research stemming from the National Geographic grant, bolstered by public donations through the crowdfunding site, will help extend the educational reach of the project beyond the Dallas-Fort Worth area through the creation of materials such as 3-D models, teaching materials, public lectures, and website articles.


Stephanie Drumheller-Horton, (865-974-2366,

Amy Blakely (865-974-5034,