A long time before they were domesticated into our best friends, dogs ran wild across North America, and the largest amongst them was Epicyon. This giant hound belongs to the family Canidae, the group that includes wolves and dogs, as well as foxes, coyotes, and jackals.
What was Epicyon?
However, unlike these modern canids, which are all part of the Caninae subfamily, Epicyon was a member of a now extinct subfamily known as Borophaginae.
The borophagines are commonly known as the ‘bone-crushing dogs’, a name that sums up exactly what this group evolved to do: crush bones and slurp up the calorie-rich marrow hidden inside. They were an incredibly diverse group, with more than 60 species currently known to science.
A lot of these species, including Epicyon, lived during the Miocene (around 15 million years ago) and dominated ecosystems across North America, occupying a similar niche to today’s hyenas.
How big was Epicyon?
There were three different species of Epicyon. The type species, known as Epicyon haydeni, was the largest of the three; measuring 2.5m in length, standing 1m tall, and weighing in at about 125kg, it was more than five times the size of an average labrador. The other two species, Epicyon aelurodontoides and Epicyon saevus, weren’t quite as large, but even they were similar in size to a modern grey wolf.
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Epicyon was by far the largest borophagine, dwarfing some of the earlier, more primitive fox-sized species such as Archaeocyon, Oxetocyon, and Rhizocyon. On average, most borophagineswere similar in size to a modern coyote, although they were a lot more stockily built. They’re also known for having huge heads, similar in shape to a lion’s, and powerful jaws that could deliver a bite stronger than any canid living today.
It’s unclear exactly why Epicyon grew so large, but it was likely in response to the evolutionary arms race that bone-crushing dogs were embroiled in with cats during the Miocene.
As a group, cats (i.e. Felidae) migrated into North America from Eurasia roughly 20 million years ago, running into the canids that had evolved on the continent some 10 million years beforehand. It was here, in Miocene North America, where the age-old rivalry between cats and dogs properly began.
Why did Epicyon become extinct?
It’s widely believed that cats - big cats, in particular - contributed towards the demise and subsequent extinction of the bone-crushing dogs. Both groups were ambush predators that relied on bursts of explosive speed to catch their prey. They had a similar taste in prey too, so almost as soon as cats arrived in North America they started competing with bone-crushing dogs.
To compete with big cats for 3m-tall camels, hippo-sized rhinos, and proto-horses - some of the most sought after prey animals of the time - bone-crushing dogs grew larger, evolving from dwarfs such as Archaeocyon to giants such as Epicyon in a little over eight million years. They also evolved stronger and stronger jaws through time, further specialising into their specific niche of bone eating.
However, they were ultimately no match for the big cats who, thanks to their retractable claws and long, powerful forelimbs, had the competitive edge when it came to grappling and killing large prey. This competition with big cats is thought to have driven Epicyon to extinction ~around 4.9 million years ago. Some borophagines survived a little longer than Epicyon, but as a group they eventually succumbed to extinction 2.5 million years ago.
What’s the biggest ever canid from the UK?
There is only one species of canid currently native to the UK, the red fox, but less than 350 years ago our islands were home to another, much larger species, the grey wolf.
The grey wolf is the largest living canid and while not nearly as large as Epicyon, nor several domesticated and selectively bred giant dog breeds, such as the English Mastiff, the Great Dane, or the Irish Wolfhound, it’s still incredibly large by canid standards. On average, wolves are 1.6m-long, 85cm tall, and weigh in at just over 40kg - although the largest ever recorded weighed double that!
The ancestors of wolves (and dogs) evolved in North America during the Miocene, alongside Epicyon and many other borophagines. Unlike their bone-crushing cousins, they successfully left North America and - across the course of roughly eight million years - spread themselves across every continent except Antarctica. They thrived in the expansive wildernesses of Eurasia and, by the Middle Pleistocene (around 400,000 years ago), had evolved into the wolves we recognise today.
The earliest known remains of wolves in the UK are found at Pontnewydd Cave in Wales and date all the way back to 225,000 years ago - a time when Homo sapiens had only just emerged in Africa and neanderthals were the only humans known in this remote part of Europe.
From other finds dated to later periods, plus written Roman and Saxon accounts, we know that wolves lived in the UK in high numbers from the Middle Pleistocene right up until the 11th century. However, their numbers dwindled during the Middle Ages as they were mercilessly hunted and by 1680 they had been entirely driven out of the country.
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