“The identification of a bone-crushing dog adds to the list of terrestrial apex predators at the Gray Fossil Site, the other being a sabertooth cat,” Bōgner said. “With two large predators on land and alligators in the water, herbivores at the site would have had to be on high alert.” 

Comparing this single limb bone with those of a wide range of modern and fossil dogs allowed the researchers to estimate the size of this extinct dog. Estimated to have weighed between 115-160 pounds, the Borophagus was similar in size to the largest living wolves.

The humerus (upper arm bone) is stout and has large areas where muscles once attached, suggesting this ancient carnivore was a powerful ambush hunter rather than a pursuit predator like wolves, researchers said.  

The Gray Fossil Site also represents a new habitat for these bone-crushing dogs.

Borophagus is known from dozens of fossil sites across the United States and Mexico but is usually found alongside plants and animals from open environments like grasslands.

Fossils at Gray paint a picture of a densely forested habitat with lots of forest plants and tree-dwelling animals. The ambush hunting strategy of bone-crushing dogs might have been particularly well-suited for hunting large herbivores in the ancient forests of the Appalachian Mountains, researchers said.

Many questions remain about the lifestyle of these extinct dogs, and the researchers are hopeful to find more Borophagus fossils at Gray.  

“The limb proportions of Borophagus are a conundrum to researchers,” Bōgner said. “Having more limb bones would be a big help in understanding how these bone-crushing dogs moved.” 

“Since the lifestyle of these dogs is thought to be similar to hyenas, I would also like to see bones that had been cracked open by Borophagus at the site,” Samuels said. “That could help us to understand what they were actually eating in the ancient Appalachian forests.”