Not long after the extinction of the dinosaurs, a now-diverse group of animals known as carnivorans split into two large groups: caniforms (dog-like animals) and feliforms (cat-like animals) says Will Newton.
This split happened roughly 50 million years ago, and just 10 million years later the first identifiable ‘dog’ appeared in North America.
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These early dogs look very different to today’s dogs, but they do share a number of similarities - adaptations that sets this group apart from other furry, four-legged mammals. Like today’s dogs, many early dogs had long muzzles, upright ears, long, slender legs, bushy tails, and specialised sets of teeth designed for cracking bones and slicing through flesh.
Together, dogs, wolves, coyotes, foxes, and their many extinct relatives belong to a family known as Canidae. There are many deadly canids alive today (e.g. grey wolves and painted dogs) but the largest and most terrifying members of this group lived during prehistory. Let’s take a look at these deadly dogs…
10 deadly prehistoric dogs
Epicyon
At 2.5m in length, 1m in height, and 125kg in weight, Epicyon is widely regarded as the largest dog that has ever lived. This bear-sized canid lived from the Late Miocene (12 million years ago) to the Early Pliocene (5 million years ago). It was native to North America and is known from fossils found across the US, as well as in Alberta, Canada.
Epicyon belongs to a subfamily of extinct dogs known as the borophagines, or the bone-crushing dogs. These dogs are known for having stout but powerfully built skulls and jaws lined with large carnassials that worked like grindstones. These specialised teeth allowed Epicyon and other borophagines to crack, crush, and chew bones, just like today’s hyenas do.
However, Epicyon was not just a bone-eating scavenger. A series of studies on the skeleton of Epicyon have revealed that it was likely an active predator that may have practiced pounce predation, relying on bursts of speed to surprise and catch its prey.
Some researchers also think Epicyon may have hunted in packs and pursued giant prey, such as the 3m-tall camel Aepycamelus.
Hesperocyon
Looking like a cross between a dog, a cat, and a raccoon, Hesperocyon has traits associated with a wide range of different carnivorans. This is because it lived just a few million years after carnivorans split into two main groups: caniforms and feliforms.
Hesperocyon belongs to the former and is widely regarded as the first dog. It may have been similar in size to today’s house cats and possessed several feline features, such as a low-slung body and a long, flexible tail, but it was unequivocally a canid based on its doggy dentition.
Hesperocyon gives its name to an extinct subfamily of dogs known as the hesperocyonines. These are considered the most primitive group of dogs and the group from which borophagines and canines (the group that includes all living dogs) emerged.
It may have been a lot smaller than many of its descendants, but Hesperocyon was still a formidable predator. Unlike later canids, it had five toes and an enlarged ‘dew claw’ that may have helped it to climb trees in pursuit of small, fast-moving prey, such as arboreal rodents. It’s also thought that Hesperocyon may have had a particular taste for plants.
Borophagus
Though it wasn’t quite as large as its close cousin Epicyon, Borophagus was better at crushing bones.
Borophagus, whose name translates to ‘gluttonous eater’, had an even more compact skull than Epicyon, with a bulging forehead and deep-set jaws. The combination of its mountain-shaped carnassials and powerful jaw muscles allowed it to crush some of the strongest bones, perhaps even femurs.
Based on the fact that fossils of Borophagus are so abundant and found across North America, it’s believed they were amongst the most successful borophagines. They also survived for a lot longer than Epicyon, facing extinction 1.8 million years ago in the Early Pleistocene. The cause of their disappearance is debated, but it's thought that competition with big cats and dire wolves may have slowly driven them to extinction.
Borophagus likely hunted a variety of different prey in much the same way that Epicyon did, and may have also hunted in packs. There weren’t many animals that were off the menu for this coyote-sized dog; their diets may have included anything from pronghorn antelopes like Cosoryx, to hippo-sized rhinos like Teleoceras.
Leptocyon
The family canidae is split into three distinct subfamilies: Hesperocyoninae, Borophaginae, and Caninae. The latter group is the only group alive today and includes everything from domestic dogs to dholes. It also includes lots of extinct relatives, such as Leptocyon - the first canine.
There were many different species of Leptocyon, as many as 11 according to some sources. Most were roughly fox-sized, but one - Leptocyon delicatus - may be the smallest canid that has ever lived, weighing less than 2kg.
While small in stature, Leptocyon was an incredibly successful predator and survived for nearly 20 million years, living from the Oligocene (30 million years ago) to the Miocene (10 million years ago). It was native to North America, like many other early dogs, and is thought to have lived in open woodlands.
Leptocyon had a long, narrow jaw and delicate teeth - the opposite of its distant cousins Borophagus and Epicyon. Instead of crushing bones, Leptocyon’s jaws were designed for catching small, fast-moving animals, such as rodents, lizards, birds, and even insects. It may have also eaten fruit.
Aelurodon
Its name may mean ‘cat tooth’, but Aelurodon was most certainly a dog. Like Borophagus and Epicyon, Aelurodon is another North American dog whose jaws were specially designed to crush bones, and pretty much anything else it could fit in its mouth.
Aelurodon’s skull resembles that of a lion’s. It had a short face, enlarged jaw muscles, and canine teeth that were rounded in cross-section, rather than elliptical like those of modern canids.
Such teeth suggest Aelurodon was better at holding on to struggling prey than other dogs. This interpretation is backed up by the fact that Aelurodon had a muscular neck, an adaptation shared with big cats. Studies of Aelurodon’s forelimbs also suggest they were adept grapplers and capable of restraining prey, much in the same way that today’s lions, tigers, and jaguars do.
Aelurodon was similar in size to a modern grey wolf and likely hunted very similar prey to its cousins, Borophagus and Epicyon. It appeared earlier than these two borophagines (around 16 mya), however, and was probably the largest of its kind for the first few million years of its existence.
Amphicyon
While not technically a canid, this list wouldn’t be complete without a mention of Amphicyon - a genus that lends its name to a group of large, predatory carnivorans known as amphicyonids, or ‘bear dogs’.
Amphicyon was discovered way back in the early 19th century but its affinities have long been disputed. It has been historically grouped with dogs (Canidae) and bears (Ursidae) - hence the name ‘bear dogs’ - though it’s now understood that it’s part of its own distinct family. This family appeared in North America in the Middle Eocene (~45 million years ago) and quickly spread to Europe, Asia, and Africa in the following periods.
Amphicyon is estimated to have reached weights of over half-a-ton, making it almost twice as large as a grizzly bear. It looked somewhat like a grizzly bear too, with a wide neck, a robust body, and massive, powerful limbs. However, its skull was more like a dog’s, with a long snout and wide jaws lined with an array of crushing and shearing teeth.
Based on Amphicyon-shaped bite marks on certain fossils, it’s thought this ‘bear dog’ had a particular taste for rhinos. How it hunted is somewhat of a mystery, though it has been suggested it may have doggedly pursued its prey before overpowering it.
Dire Wolf
These extinct wolves have garnered quite a lot of public attention in recent years; not only due to their monstrous depiction in George R.R. Martin’s epic fantasy series A Song of Ice and Fire, but also as a result of Colossal Biosciences’ latest attempt to ‘de-extinct’ them.
It’s a common thought that today’s wolves - grey wolves and their many subspecies - are descended from dire wolf stock. However, a recent study on dire wolf DNA has revealed that this is not the case. Instead of being the closest ancestors of extant grey wolves, as was historically thought, dire wolves are actually evolutionary distant cousins that broke away from the wolf family tree some 5.5 million years ago.
While they may look a lot like living wolves, there are several key differences. For starters, dire wolves were roughly 40% larger than today’s average-sized wolves. They had larger teeth and stronger jaws too - no doubt adaptations for hunting big game, such as horses, bison, camels, and ground sloths. They may have also sport shorter coats of reddish-brown fur.
As a species, dire wolves lived from 125,000 to 10,000 years ago and were native to the Americas, ranging from southern Canada to Central and South America. Their remains have been found across a broad range of habitats, including plains, grasslands, arid savannahs, and forested mountains.
Eucyon
This extinct canid is a descendant of Leptocyon and widely believed to be the progenitor of the genus Canis - the genus that comprises almost all living canids, including wolves, coyotes, and domestic dogs.
Eucyon lived from the Late Miocene (10.3 million years ago) to the Late Pliocene (3.6 million years ago) and, like many of the prehistoric dogs on this list, was native to North America. However, it did explore lands further afield. Based on finds of Eucyon fossils, it’s believed they spread to Asia roughly six million years ago and, across the course of the next few million years, made it as far as western Europe and eastern Africa.
At roughly 15kg, Eucyon was about the same size as a Beagle, though it was slender and built more like a modern jackal. Eucyon also had larger frontal sinuses than its ancestors - a sign that dogs were becoming increasingly more reliant on their sense of smell.
The largest species of Eucyon, Eucyon ferox, is thought to have had a hypercarnivorous diet and preyed on a variety of small to medium-sized mammals. Other species of Eucyon were likely mesocarnivores, meaning they supplemented their meat-based diets with a variety of plants and possibly even fruits.
Armbruster’s Wolf
Discovered in 1913 and described from a series of fossils found in the aptly named Cumberland Bone Cave in Maryland, US, Armbruster’s wolf is an extinct species of wolf that has been proposed as the ancestor of the infamous dire wolf.
The affinities of Armbruster’s wolf have been debated ever since its discovery, but a 2021 study on dire wolf DNA shifted the consensus towards the hypothesis that the two wolves belong to a highly divergent lineage of extinct wolves that last shared a common ancestor with modern wolves more than 5.5 million years ago. This has led some to suggest that Armbruster’s wolf and its supposed descendant, the dire wolf, should be grouped under the distinct genus Aenoncyon, rather than Canis.
Like dire wolves, Armbruster’s wolves were a lot larger than modern wolves, with larger teeth and stronger jaws. These size differences likely allowed them to hunt larger prey, such as ground sloths and maybe even mammoths.
Armbruster’s wolf lived during the Middle Pleistocene, several hundred thousand years before the dire wolf appeared in the Late Pleistocene. Its range was a lot smaller than that of the dire wolf’s and it was largely confined to what is now the US.
Xenocyon
It’s no surprise that an animal whose name means ‘strange dog’ has caused a headache for taxonomists ever since it was discovered in the early 20th century.
Historically, Xenocyon has been considered a subgenus of Canis, or synonymous with Lycaon - the genus that includes painted dogs. This confusion surrounding Xenocyon’s affinity is down to the similarities it shares with several living dogs. The largest species, Xenocyon lycanoides, is estimated to have weighed roughly 40kg, which makes it a similar size to a large painted dog and just a tad smaller than a grey wolf.
Xenocyon looks like a powerfully built, wolf-like painted dog, with long and gracile legs, a rigid spine, and highly digitigrade feet - adaptations for pursuing prey at speed for long distances. To kill its prey, Xenocyon used its blade-like canines and elongated carnassials to slice through large sections of flesh and inflict devastating wounds. On the menu for Xenocyon were a variety of large mammals, including antelope, deer, baboons, and even elephant calves.
Xenocyon lived from the Late Pliocene to the Early Pleistocene (between three and two million years ago) and is the only prehistoric dog on this list not native to North America. Instead, it’s believed Xenocyon first appeared in East Asia before spreading as far south as southern Africa and as far west as the Iberian Peninsula. It also spread to parts of North America during the latter years of its existence.
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