One was Hesperosuchus agilis, a fast land predator with a long snout, powerful hind legs, and smaller, more slender front limbs. It likely searched for prey along rivers and streams.

The second animal had a noticeably different head. Its snout was shorter, its skull was more strongly reinforced, and its enlarged jaw muscles would have helped it snap down on larger prey.

Neither animal escaped the sudden event that followed. Researchers believe both died at the same time, possibly during a flash flood or mudslide. Their remains were buried together, and favorable chemical conditions preserved their bones through the "Age of Reptiles," the later rise of mammals, and their eventual excavation in large blocks of rock now housed at the Peabody Museum of Natural History at Yale.

A New Species Emerges From an Old Fossil

After closely examining the short-snouted animal, Yale paleontologists determined that it belonged to a previously unknown species. They named it Eosphorosuchus lacrimosa in a new study.

"This speaks to the diversification of proto-crocs toward the beginning of the 'Age of Reptiles,'" said Bhart-Anjan Bhullar, associate professor of Earth and planetary sciences in Yale's Faculty of Arts and Sciences (FAS), associate curator of vertebrate paleontology and vertebrate zoology at the Peabody Museum, and senior author of the new study published in the journal Proceedings of the Royal Society B.

"During this period, the late Triassic, there were two reptile dynasties vying for dominance: the line that would produce crocodiles and alligators on one side, and that which would produce birds, which of course are dinosaurs, on the other," Bhullar added. "The dinosaurs at this time were slim, delicate animals that walked on two slender legs almost like herons, and the crocodiles were fast-running, four-legged predators, low-slung and more heavily built -- analogous to a jackal, a big fox, or a dog."

During the late Triassic, the ancestors of crocodiles and the lineage that produced dinosaurs were both beginning to expand into new ecological roles. Unlike today's mostly aquatic crocodilians, many early crocodile relatives were agile predators that ran across land.

A Rare Window Into the Late Triassic

Reconstructing the diversity of life in a particular place and time can be difficult for paleontologists. Fossils are often incomplete, and researchers cannot always determine whether animals found in the same rock layer actually lived together.

Exceptionally preserved fossil sites can provide much clearer evidence. Ghost Ranch in New Mexico is one such location.

For about a century, scientists have studied fossils from Ghost Ranch that include near-crocodiles, lizard relatives, fish, and dinosaurs (most prominently, the carnivorous Coelophysis bauri). The Yale Peabody Museum holds two large sections of rock from the "Ghost Ranch Bone Bed." Together, the blocks are roughly the size of a car.

The fossil containing the two crocodile relatives was excavated in 1948. Although it had been available to scientists for about 75 years, it had never been fully analyzed or formally identified.

"I had been staring at this fossil for a while," Bhullar said. "For years, both Ghost Ranch crocs were thought to be examples of Hesperosuchus, but it looked like the Yale animal had a different facial structure."

CT Scans Reveal Hidden Anatomy

To investigate those differences, Miranda Margulis-Ohnuma, a Ph.D. student in Earth and planetary sciences in Yale's Graduate School of Arts and Sciences (GSAS), studied a computed tomography (CT) scan of the animal. The scan was performed at the Yale Chemical and Biophysical Imaging Center by former Peabody Museum senior preparator Marilyn Fox.

CT imaging allowed Margulis-Ohnuma to examine structures that remained embedded in the rock. She digitally "disassembled" the fossil one bone at a time and uncovered several anatomical features that differed from known Hesperosuchus specimens.

Those differences supported the identification of Eosphorosuchus as a separate genus and species.

The name combines Eosphorus, the Greek god known as the "dawn-bringer," with the Greek word "soukhos," meaning crocodile.

"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 Margulis-Ohnuma, who is first author of the new study. "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."

Early Crocodile Relatives Hunted Differently

The discovery is especially valuable because the two animals appear to have lived in the same ecosystem at the same time. Their contrasting skulls and jaws suggest that closely related predators were already dividing up available food resources by developing different feeding strategies.

Hesperosuchus had a longer, narrower snout, while Eosphorosuchus had a shorter and more heavily reinforced skull with stronger jaw muscles. These differences may have reduced direct competition by allowing the animals to pursue different kinds of prey.

"It's a time-slice of a single moment 210 million years ago," Bhullar said. "These two individuals had to compete and interact with each other. They were quite possibly looking at each other when they died."

Co-authors of the study are Alexander Ruebenstahl, a current student at Yale GSAS, and recent Yale graduate Dalton Meyer '25 Ph.D., who is now a lecturer at Roanoke College.

What Is Eosphorosuchus lacrimosa?

Eosphorosuchus lacrimosa was an extinct proto-crocodile identified by Yale University researchers. It was a fast-running land predator that lived near rivers and lakes about 210 million years ago.

Why Is Eosphorosuchus lacrimosa Important?

Eosphorosuchus lacrimosa offers evidence that early crocodile relatives were already developing different feeding adaptations near the beginning of the "Age of Reptiles," during the late Triassic Period, 252 to 201 million years ago.

Its presence beside Hesperosuchus gives researchers a rare view of two related predators occupying different ecological roles within the same ancient environment.

What Did Eosphorosuchus lacrimosa Look Like?

According to Yale paleontologists, Eosphorosuchus lacrimosa had a short snout, a heavily reinforced skull, and enlarged jaw muscles suited for snapping shut on large prey. It also had large hind legs and smaller, thinner front limbs.