GRAY, Tenn. (WJHL) — The extinct genus is called Borophagus, meaning “gluttonous eater” — and now researchers have learned the giant bone-crushing dog was present at the Pliocene-era Gray Fossil site.

The confirmation of a humerus (upper arm) bone of the species means the site is now confirmed to have had two species of “terrestrial apex predators,” or land animals atop the food chain, as well as alligators, another apex predator. The remains of at least one sabertooth cat also have been discovered at Gray.

ETSU paleontologist Joshua Samuels with the humerus bone of what has now been confirmed to be a bone-crushing dog of the genus Borophagus. (WJHL photo)

“When you come to a site like this … what was living here, what was eating what, that idea of what’s at the top of the food chain is something people really want to know and so this dog is exactly filling that role,” East Tennessee State University (ETSU) Associate Paleontology Professor Joshua Samuels told News Channel 11 Monday. “So the idea of things like bone crushing dogs, sabertooth cats – they get people excited.”

Samuels called Borophagus “a dog unlike anything alive today.” He said it had powerful forelegs and was probably an ambush hunter as evidenced by the presence of large areas where muscles were once attached.

“It had these teeth adapted to cracking bones like a hyena does and it was probably well suited to the forest here – jumping on prey from cover.”

Other than the rhinoceroses and mastodons that existed at the site 4.5 to 5 million years ago, most of the other inhabitants couldn’t have repelled the fierce predator.

“The tapirs, horses, things like that, they didn’t have much of a chance.”

Samuels and ETSU masters paleontology graduate Emily Bōgner worked to confirm what animal the bone belonged to. It was actually discovered about a decade ago. Samuels said.

“It was recognized that it was from some kind of a predator but people weren’t sure exactly what it was,” Samuels said.

But Samuels, who began working at ETSU in 2016, has researched the limbs of extinct carnivores to help understand how they lived.

Artist’s illustration of the ancient bone-crushing dog which was likely very similar to the Gray Fossil Site dog. Artwork by Mauricio Antón.

“I had seen things like this before and I said, ‘we can figure this out.’ And (Bōgner) … worked really hard, did a lot of work figuring out and comparing this to lots of different kinds of dogs and helped reveal, ‘yeah, we’re sure it’s this dog.’”

The pair published a study on their findings in a recent Journal of Paleontology issue. According to a Cambridge University Press article published July 25, the discovery marks “the first occurrence of this genus in a heavily forested ecosystem.”

Samuels said researchers hope to find additional evidence to tell them more about the species’ behavior and lifestyle at the site, which has different characteristics than most places in North America that Borophagus has been discovered. The 50 or so other sites where Borophagus has been discovered in the U.S. are typically grassland-dominated.

The species has been found all around North America, “but it hadn’t been found in this kind of forest mountain environment before.”

Samuels said the discovery lends to the theory that Borophagus was a very common top predator, much like wolves are in places where humanity hasn’t diminished them.

Samuels said this specimen weighed in at between 115 and 160 pounds, a similar size to the largest wolves living today.

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. The presence of just one bone, so far at least, leaves many questions unanswered.

Emily Bōgner (left) and fellow student Julia Schap (right) during their time as graduate students in ETSU’s Paleontology Program. Photo from Josh Samuels.

“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.”

According to the Cambridge article, the specimen was estimated to be between 8 and 12 months old based on characteristics of the bone. It is located at ETSU’s Museum of Natural History.

The article also states that because of the Gray Fossil Site’s age “the conspicuous absence of Borophagus from the (site) was previously noted by multiple researchers.”

“There’s a lot of things where until someone sees them who has an idea what it is it can be hard to figure out,” Samuels said.

A closeup of the Borophagus upper arm bone found at the Gray Fossil Site. (WJHL photo)

“Unless you’ve got things like teeth, a lot of times it’s really hard to say, ‘I’m sure it’s this – I’m sure it’s this kind of dog and not another,'” he said. “It just so happens this one is really distinctive, and so it’s something where comparing it to skeletons found other places we can say, ‘yeah, it’s this dog.’”

What ETSU doesn’t yet know is what specific species of Borophagus they unearthed. There are several.

“We could say ‘it’s this species or it’s this species,’ but we can’t quite nail it down. If we had teeth, we could do that.”

Samuels is hopeful more specimens of this dog will be unearthed. When the red panda and badger that were discovered at the site were first dug up, it was just a tooth or a few teeth. Now ETSU has multiple complete skulls of those animals and can say much more about what they were doing at the site and how they lived.

Borophagus is one of about 100 animal species discovered so far at the site.

“We’ve just scratched the surface of the site, and so just a few percent of what’s here to be dug up has been dug up yet,” Samuels said. “So there’s lots more new species that will be found here as time goes on we’re certain to find new things and maybe we’ll find more of these dogs.”