Two hundred ten million years ago, two crocodile cousins tragically died side by side, according to Yale paleontologists who discovered this significant moment in time when crocodiles were diversifying before the rise of the dinosaurs.

First author Margulis-Ohnuma described the discovery as a “time slice.” The two new fossils uncovered in New Mexico provided Yale researchers with a rare snapshot of the diversification of proto-crocodiles at the dawn of the “Age of Reptiles.”

The fossils represent two proto-croc cousins who had to compete and interact with each other. They were “quite possibly looking at each other when they died,” likely due to a flash flood.

Although an unforeseen event may have taken their lives, their bones were preserved for over 200 million years. Eventually, they found a home within large blocks of rock at the Peabody Museum of Natural History at Yale, where the authors of a new study discovered them.

The lack of physical evidence presents significant challenges for the field of paleontology in understanding species diversification at specific times and places on Earth. This latest discovery is uniquely thrilling, as the flash flood captured these unsuspecting cousins in a moment of daily life.

Same same but different

During the Triassic period, two reptile dynasties competed for dominance. One lineage would give rise to crocodiles and alligators, while the other would produce dinosaurs and the birds that would eventually conquer the skies. At this time, researchers explained, dinosaurs were slender-legged animals akin to herons, while four-legged crocodiles were the canines of the era.

A press release from Yale described the ecosystem before the Age of Reptiles as “sufficiently rich.” Close relatives developed specialized feeding anatomy to share resources. One can imagine that as species were diversifying during this time, they suddenly found they were different from their own kind, yet still related. To maintain harmony, they learned how to adapt and live with one another, even if they did compete (or bicker).

To investigate their anatomy, Miranda Margulis-Ohnuma, a Ph.D. student in Earth and planetary sciences in Yale’s Graduate School of Arts and Sciences (GSAS), conducted computed tomography (CT) scans of the crocodile, digitally disassembling the fossil bone by bone and revealing several variations of the Hesperosuchus species.

Cousins on the brink of the age of the dinosaurs

About the size of jackals, these cousins once roamed a riverbank in New Mexico. The long-snouted Hesperosuchus agilis hunted for food near rivers and streams using large back legs and smaller, thinner arms. On this fateful day, he was not alone; he was accompanied by his shorter-snouted cousin, identified as a new species named Eosphorosuchus lacrimosa. His robust jaw muscles gave him an advantage at snapping at large prey.

“Eosphorosuchus is one of only a handful of well-preserved early crocodile relatives, and its coexistence with Hesperosuchus represents the ‘dawn’ of functional diversification in the lineage that would give rise to modern crocodiles,” said first author Margulis-Ohnuma in a press release by Yale.

“In addition to its unique anatomy and preservational history, the specimen demonstrates the potential of existing museum collections to continue revealing novel insights into the history of life.”