Locked in stone for 210 million years, this newly identified crocodile cousin was built to crush larger prey

On a fateful day 210 million years ago, two crocodile cousins about the size of jackals stood side-by-side amid the low ferns of a humid riverbank that would one day become northern New Mexico. One of the crocs, Hesperosuchus agilis, had a long snout, large back legs, and smaller, thinner arms. A land dweller, Hesperosuchus was speedy and liked to hunt for food near rivers and streams.

His companion, though of similar size, cut a different swath through the prehistoric shrubs. He had a shorter snout, a more reinforced skull, and expanded jaw muscles perfect for snapping shut on large prey. Not that any of these physical attributes could forestall his ultimate destiny.

Both crocs died in the same instant, apparently the result of a natural disaster such as a sudden mudslide or flash flood. They remained buried together—their bones preserved thanks to fortuitous geochemical forces—right on through the “Age of Reptiles,” the rise of mammals that followed, and the crocs’ eventual excavation within large blocks of rock that are part of the collections of the Peabody Museum of Natural History at Yale.

That’s how a team of Yale paleontologists came to identify the short-snouted croc as a separate species, which they’ve named 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: Biological Sciences.

“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.”

It can be challenging for paleontologists to fully understand the species diversity of a specific time and place in Earth’s distant past, Bhullar said, primarily due to the lack of physical evidence left behind and the lack of certainty about whether fossils preserved in a mass of rock were actually from the same time and place. But on rare occasions, researchers find a site that is exceptionally well preserved.

Such is the case in Ghost Ranch, New Mexico, where dozens of near-crocodiles, lizard relatives, fish, and dinosaurs (most prominently, the carnivorous Coelophysis bauri) have been discovered and debated for the past century. Two sections of excavated rock from the “Ghost Ranch Bone Bed”—together about the size of a car—are at the Yale Peabody Museum.

Excavated in 1948, the fossil has been known to science for three-quarters of a century, but it was never fully examined or 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.”

For the new research, Miranda Margulis-Ohnuma, a Ph.D. student in Earth and planetary sciences in Yale’s Graduate School of Arts and Sciences (GSAS), began to work on a computed tomography (CT) scan of the crocodile, performed at the Yale Chemical and Biophysical Imaging Center by former Peabody Museum senior preparator Marilyn Fox, who was an undergraduate in Bhullar’s lab.

Using that technology, Margulis-Ohnuma was able to digitally “disassemble” the fossil, bone by bone, revealing several variations from known examples of Hesperosuchus.

Enter Eosphorosuchus, named for the Greek god Eosphorus, the “dawn-bringer,” and the Greek word “soukhos,” which means 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.”

What makes the discovery particularly compelling, researchers say, is the fact that it provides a snapshot of a long-ago ecosystem whose biodiversity was sufficiently rich that close relatives partitioned their ecological roles by specializing their feeding anatomy.

“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.”