While it may belong to the same family as dogs,\u00a0Epicyon\u00a0wasn\u2019t anything like our beloved golden retrievers<\/a>, french bulldogs, cocker spaniels<\/a>, or border collies<\/a>. It was part of a fearsome subfamily of canids known as the borophagines, or \u2018bone-crushing dogs\u2019, and it was one of the top predators of its time, occupying a similar niche to today\u2019s hyenas.<\/p>\n The\u00a0borophagines\u00a0were an incredibly diverse group, boasting more than 60 species. All of these species were endemic to North America and like\u00a0Epicyon\u00a0they also dominated ecosystems across the continent for millions of years.<\/p>\n Some species of borophagines outlived\u00a0Epicyon\u00a0and survived until the Early Pleistocene, meaning they lived long enough to see the onset of the ice age <\/a>and the arrival of many iconic, cold-adapted megafauna.<\/p>\n How large was Epicyon? There were three different species of\u00a0Epicyon, but it\u2019s the type species –\u00a0Epicyon haydeni\u00a0– that holds the title of \u2018the largest dog that ever lived\u2019.<\/p>\n At 2.5m in length, 1m in height, and\u00a0125kg\u00a0in weight, this particular species of\u00a0Epicyon\u00a0was more comparable in size to a brown bear<\/a> than your average labrador<\/a>. The other two species,\u00a0Epicyon\u00a0aelurodontoides\u00a0and\u00a0Epicyon\u00a0saevus, were smaller, but even they were similar in size to a modern grey wolf.<\/p>\n Not all\u00a0borophagines\u00a0were giants like\u00a0Epicyon. Some of the earliest and most primitive members of this large subfamily, such as\u00a0Archaeocyon,\u00a0Oxetocyon, and\u00a0Rhizocyon, were no larger than today\u2019s foxes. They were also considerably slower than\u00a0Epicyon\u00a0and 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.<\/p>\n 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\u2019s dogs and wolves. However, as a result of its large size, researchers think it wasn\u2019t able to run quite as far as modern canids and instead relied on bursts of speed to catch its dinner.<\/p>\n What did Epicyon eat?<\/p>\n Epicyon\u00a0and other borophagines were hypercarnivores, surviving on diets that consisted of more than 70% meat. They also ate\u00a0a lot\u00a0of bones and are thought to have cracked them open in an attempt to get at the calorie-rich marrow hidden inside.\u00a0<\/p>\n 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\u00a0Epicyon\u00a0have also been found to contain fragments of bone, suggesting they were not only capable of crushing, chewing, and swallowing bone, but digesting it too.<\/p>\n In order to crush bones,\u00a0Epicyon\u00a0relied 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.\u00a0Epicyon\u00a0also had a huge head, similar in shape to a lion\u2019s, and powerful jaws that could deliver a bite stronger than any canid living today.<\/p>\n Based on\u00a0Epicyon\u2019s fondness for bones, it was originally hypothesised that it was a scavenger, but it\u2019s now thought that it was an active predator, and perhaps one that even hunted in packs. If they did hunt in packs,\u00a0Epicyon\u00a0may have been able to bring down prey larger than themselves, such as the 3m-tall camel\u00a0Aepycamelus\u00a0or the hippo-sized rhino\u00a0Teleoceras, which also lived in North America during the Miocene.<\/p>\n Why did Epicyon become extinct?<\/p>\n Epicyon\u00a0faced extinction roughly five million years ago and while some\u00a0borophagines\u00a0held 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\u00a0bone-crushing dogs faced extinction, but the most popular is that the oldest foes of dogs, cats, ultimately contributed to their demise.<\/p>\n 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.\u00a0<\/p>\n
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Skeletal mount of\u00a0Epicyon haydeni\u00a0(LACM 7756\/154454) on display at the Natural History Museum of Los Angeles County. Jonathan Chen, CC BY-SA 4.0 https:\/\/creativecommons.org\/licenses\/by-sa\/4.0, via Wikimedia Commons<\/p>\n