This ancient giant dog wasn’t anything like our beloved pooches today, it was more comparable in size to a brown bear .
What was Epicyon?
Epicyon belongs to the family Canidae, the group that includes wolves and dogs, as well as foxes, coyotes, and jackals. It lived from the Early Miocene (around 16.3 million years ago) right up until the Early Pliocene (about 4.9 million years ago), ranging across North America from Alberta, Canada, to Florida, US.
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While it may belong to the same family as dogs, Epicyon wasn’t anything like our beloved golden retrievers, french bulldogs, cocker spaniels, or border collies. It was part of a fearsome subfamily of canids known as the borophagines, or ‘bone-crushing dogs’, and it was one of the top predators of its time, occupying a similar niche to today’s hyenas.
The borophagines were an incredibly diverse group, boasting more than 60 species. All of these species were endemic to North America and like Epicyon they also dominated ecosystems across the continent for millions of years.
Some species of borophagines outlived Epicyon and survived until the Early Pleistocene, meaning they lived long enough to see the onset of the ice age and the arrival of many iconic, cold-adapted megafauna.
How large was Epicyon?
There were three different species of Epicyon, but it’s the type species - Epicyon haydeni - that holds the title of ‘the largest dog that ever lived’.
At 2.5m in length, 1m in height, and 125kg in weight, this particular species of Epicyon was more comparable in size to a brown bear than your average labrador. The other two species, Epicyon aelurodontoides and Epicyon saevus, were smaller, but even they were similar in size to a modern grey wolf.
Not all borophagines were giants like Epicyon. Some of the earliest and most primitive members of this large subfamily, such as Archaeocyon, Oxetocyon, and Rhizocyon, were no larger than today’s foxes. They were also considerably slower than Epicyon and later borophagines, retaining the same primitive, plantigrade posture (i.e. flat footed) that their ancestors from the Early Oligocene (~34 to 28 million years ago) had.
Epicyon, on the other hand, had a digitigrade posture, meaning it walked (and ran) on its toes while the rest of its foot was lifted. It also had small collarbones and a flexible back - two more adaptations that suggest it was built for running and chasing down prey, just like today’s dogs and wolves. However, as a result of its large size, researchers think it wasn’t able to run quite as far as modern canids and instead relied on bursts of speed to catch its dinner.
What did Epicyon eat?
Epicyon and other borophagines were hypercarnivores, surviving on diets that consisted of more than 70% meat. They also ate a lot of bones and are thought to have cracked them open in an attempt to get at the calorie-rich marrow hidden inside.
This bone-eating behaviour is evidenced by the patterns of wear on their teeth, which closely resemble those observed on the teeth of hyenas - another bone-crushing hypercarnivore. Some samples of fossilised faces from Epicyon have also been found to contain fragments of bone, suggesting they were not only capable of crushing, chewing, and swallowing bone, but digesting it too.
In order to crush bones, Epicyon relied on a set of robust, specially designed cheek teeth known as carnassials. These mountain-shaped gnashers locked together to create a powerful crushing surface that was capable of cracking anything from large leg bones to small skull fragments. Epicyon also had a huge head, similar in shape to a lion’s, and powerful jaws that could deliver a bite stronger than any canid living today.
Based on Epicyon’s fondness for bones, it was originally hypothesised that it was a scavenger, but it’s now thought that it was an active predator, and perhaps one that even hunted in packs. If they did hunt in packs, Epicyon may have been able to bring down prey larger than themselves, such as the 3m-tall camel Aepycamelus or the hippo-sized rhino Teleoceras, which also lived in North America during the Miocene.
Why did Epicyon become extinct?
Epicyon faced extinction roughly five million years ago and while some borophagines held on for another few million years, the group eventually met their end 2.5 million years ago. There are several theories as to why the bone-crushing dogs faced extinction, but the most popular is that the oldest foes of dogs, cats, ultimately contributed to their demise.
As a group, cats (i.e. Felidae) emerged in Eurasia 33 million years ago. Some 14 million years later, they migrated into North America via the land bridge that once connected Russia and Alaska, running into the canids that had lived there for more than 10 million years. It took cats a few million years to gain an ecological foothold in North America, but once they did they began to take over niches once occupied by canids, specifically borophagines.
Like the bone-crushing dogs, the cats that migrated into North America from Eurasia were also ambush predators and had a similar taste in prey. However, with retractable claws, powerful forelimbs, and - in the case of the sabre-tooth cats - throat-puncturing canines, these prehistoric cats were much better equipped for grappling and killing large herbivores.
As Epicyon and other borophagines were outcompeted by cats, the ancestors of today’s dogs and wolves specialised even further into their specific niche of long distance pursuit hunting. This served them well and by roughly eight million years ago they had entered Eurasia and spread themselves across the continent. From there they prospered, evolving into the 37 species that live amongst us today - including the furry friend that may be lying next to you now, snoring as you read this article.
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