Courtesy of Kelsey Jenkins

Much remains unknown about how Earth’s species bounced back from the Permian-Triassic extinction event, also known as “the Great Dying.” This was the planet’s most severe extinction event, responsible for killing around 90 percent of species 252 million years ago. 

A new Yale study of a 250-million-year-old reptile fossil may provide insights into the event’s aftermath.

The study was a product of a collaboration between researchers from three universities: Yale, Sam Houston State University and the University of the Witwatersrand. Kelsey Jenkins GRD ’23, a doctoral student in the Department of Earth & Planetary Sciences, was the lead author on the paper. The study’s analysis of a 250-million-year-old reptile fossil, a Palacrodon specimen, from Antarctica may begin to fill in some of the evolutionary gaps.

The team of scientists used computed tomographic scanning technology, also known as CT scanning, as well as microscopy to create 3D renderings of the Palacrodon specimen. 

The study was co-authored by Bhart-Anjan S. Bhullar, assistant professor of earth and planetary science at Yale, whose lab specializes in novel applications of the technology. Bhullar used his expertise to help the team leverage the CT scans to provide new insights into the specimen’s physical features. 

“What we learned from its bones is that this reptile exhibits a transitional version of hearing,” Jenkins told the News. “Older reptiles have a really cruddy ear that they inherited from their ancestors that didn’t need to be able to hear on land. Meanwhile, modern reptiles are mostly capable of hearing high-frequency sounds. Palacrodon fills in the anatomical gap when it comes to hearing.”

Jenkins explained that this anatomical observation is useful for understanding how the Permian-Triassic extinction event changed how reptiles needed to hear and has broader implications for how the event changed life on earth hundreds of millions of years ago. She also noted that despite the Permian-Triassic event killing many plant species, the Palacrodon fossil shows early adaptations for eating plants. Jenkins pointed out that this challenges conventional wisdom on the ecosystems in which the recovery from the extinction event took place. Indeed, the researchers concluded in the study that their findings “support the  presence of some robust vegetation during the end-Permian mass extinction recovery phase.”

Dalton Meyer GRD ’23, a co-author on the study and doctoral student in the Department of Earth and Planetary Sciences, credits the study’s success to the use of CT imaging. Meyer told the News that the way the specimen was treated when it was found in the 1990s would have prohibited the researchers from properly examining the fossil.

“The latex peel [from the 90s] has been lost, and with it much of the information about the surface of the specimen,” Meyer said. “So CT imaging allowed us to look at something that was otherwise lost and hidden from the naked eye. … It also allowed us for the first time to peer inside of the rock matrix that holds the specimen, where we found bones that weren’t even exposed at the surface, and that had never been seen before.”

The Palacrodon fossil is housed in the collections of the University of the Witwatersrand, and the inspiration for the study was Jenkins’ master’s thesis project on South African Palacrodon specimens at Sam Houston State University.

Jenkins said that having the chance to study the fossil from Antarctica, the most complete known Palacrodon, was very exciting to her after having analyzed Palacrodons that were “mostly broken teeth” for her graduate studies. She was especially intrigued by the breakthroughs in understanding other early reptile specimens could offer in the fields of paleoecology and evolutionary biology.

“Palacrodon is just one of many early reptiles that can inform our science about paleoecology and major anatomical transitions in the history of their evolution,” Jenkins said. “I’m currently untangling the anatomy of several other early weird little critters to understand how different sensory systems like hearing and vision have evolved hundreds of millions of years ago.”

Likewise, Meyer told the News that “in an ideal world” his next steps would be to return to Antarctica to look for more fossils that could provide new information about the post-Permian world. In the meantime, he hopes the study has spotlighted the power of examining fossils with new technological methods. 

The study was published in the Journal of Anatomy in early September.