Frog Fossil

Virginia Tech Assistant Professor Michelle Stocker holds a rock with an enbedded Chinle frog hipbone fossil.

This past summer a paleontological team led by Virginia Tech professors Sterling Nesbitt and Michelle Stocker discovered an extremely rare frog fossil in the Chinle formation near Petrified Forest National Park in Arizona. The fossil is from the hipbone of an ancient amphibian in the total group or “clade” Salientia which includes the orders of frogs and toads both living and extinct.

According to Nesbitt and Stocker, this fossil is the first of its kind because it comes from an area that was equatorial during the Triassic. Only two other examples of Triassic frog fossils were found in locations that were not near the equator during this period, making the finding especially rare and valuable.

The fossil helps scientists fill in some of the gaps in the paleontological record. The fossil is dated between the two other Triassic frog fossils and leads the researchers to believe that frog species were widespread and existed throughout the Triassic. The existence of the fossil also helps fill out the ancient biome of Petrified Forest National Park and the surrounding areas.

The frog fossil, the bones of several other ancient aquatic animals, such as lungfish, and the type of rocks found at the site lead the researchers to believe that the area was once part of a gentle river containing large horsetail-like plants and giant trees.

“The environment at the time was very different from how you or I would think of a river,” Nesbitt said. “There were no angiosperms (flowering plants) at the time.”

The fossil is only about the size of an eyelash. According to Nesbitt, the fossil was mostly discovered on accident as the team was looking through a section of rock that the team knew small fossils were present in. This section was part of an ancient fluvial deposit which is composed of layers of sediment slowly piled up over millions of years and hardened by pressure from the buildup of these layers as well as other factors.

The section of the deposit the fossil was found in is an old section composed of light green and white layers, which contained teeth of various prehistoric river animals. Tooth fossils are the most common small animal fossils as teeth are relatively harder than many other bones, especially in small creatures. The teeth gave the researchers clues to where they might find interesting fossils. This led them to discover the frog fossil due to its proximity to these other fossils.

“When you’re splitting rocks, you don’t know what you’re going to find,” Stocker said. “It’s a lot like turning a page in a book; you don’t know what’s inside until you turn the page.”

The researchers believe that they have discovered a new species, but are hesitant to name it. The small size of the fossil gives little information about what the animal actually looked like, so they would like to gather more samples, hopefully from different body parts. They do know, however, that the bone is from a frog due to its shape and texture.

“We don’t want to give the frog a name just yet,” Nesbitt said. “We would like to get a better sample for the official species picture.”

The team plans to go back to the formation this summer to try to find more samples of this frog species and perhaps find skeletons from other amphibians as well.

Students interested in participating in these digs and paleontology in general can attend the department’s Paleo Lab Night, held every Tuesday during the school year from 6:30 p.m. to 8:30 p.m.

In these labs, which are open to Hokies of all majors, students can help clean and prepare real fossils that the team has excavated from various sites. Students do not need any prior knowledge to attend these meetings and can work their way up to working more in depth with paleontology. To attend the digs, undergraduate students can apply for an internship with the team. However, spots are usually limited to three interns per semester. Applications for this year’s dig are over. However, applications for next year’s internship begin in January.