16-18 million years ago, a fierce predator roamed the North American landscape. It had a long snout and a long tail like a modern day wolf, but it also had a stocky build, powerful forelimbs, plantigrade feet (i.e. it walked with its paws flat on the ground) and grew up to 2.5 metres long and 1.5 metres tall. These latter characteristics are much more like a modern bear. This was a weird mix of features. Anybody seeing this animal today, not knowing what it was, would think to themselves; “Is that a mutated bear?” “Or is it a new dog breed?”. This animal has the scientific name Amphicyon, meaning “Ambiguous dog”, however its common nickname is “Bear-Dog”. This is fitting because Amphicyon looks like an animal that would be the result of bizarre genetic cross-breeding of a Labrador and a Grizzly Bear! So the question that I will ask in this blog is, what in the world was it?
The genus Amphicyon (genus being a group of species, i.e. like the big cat group) was a very successful animal in its time, with multiple species stretching across the globe from North America to Europe to Africa. These species included Amphicyon longirams, which stalked what is now Florida, and Amphicyon Ingens; which reached a size comparable to the largest terrestrial carnivore alive today – the Polar Bear. In 2016 there was even a Chinese species discovered which was named Amphicyon zhanxiangi. Amphicyon first evolved in Europe and Asia, before migrating into North America during the mid-Miocene period 18 Million years ago. From this period they out-competed the resident mammalian carnivores such as the Hyaenodonts (large mammalian predators with shearing teeth), the Entelodonts (who have the awesome nickname of “Terminator Pigs”) and other Bear-Dogs to become the top dog (pun intended) of the Miocene landscape.
Bear-Dogs as a whole are thought to have had a variety of hunting strategies that varied between species. Amphicyon, being larger and more stocky in build, would have hunted somewhat like a bear; surprising their prey and pursuing it for a short distance before using their muscular forelimbs and large body size to pin it down before biting at the neck and body to finish it off. Being an ambush hunter it wouldn’t have regularly partaken in long chases, though it was able to pursue prey for longer than other ambush predators. Their size would have allowed them to hunt larger mammalian herbivores, which would have included early rhinos. We know this from a fossil unearthed from Portugal of the lower jaw of the extinct rhino Iberotherium. This jaw has clear puncture marks in it made by the teeth of a large carnivore. A study, conducted by Antunes, Balbino and Ginsberg in 2006, concluded that the culprit was Amphicyon giganteus as it was the only known carnivore from the same time and place large enough to inflict these type of wounds (though whether it did so when hunting or scavenging this Iberotherium is unknown). Meanwhile other species of Bear-Dogs, such as Borocyon, had longer legs and more slender bodies. This suggests that they hunted more like modern day wolves; pursuing their prey over long distances. While Amphicyons diet would have mostly consisted of meat it is thought that other Bear-Dogs might also have been omnivorous to a degree, eating plant matter and berries to supplement their diet. It is also thought that they, along with other Bear-Dogs, exhibited denning behaviour, digging out burrows in which they could raise their young and take shelter. Like all mammals they would have exhibited high levels of parental care, raising pups until they were old enough to fend for themselves. Amphicyon also exhibited sexual dimorphism, just like bears, with the males being substantially larger than the females.
So to answer the question posed at the beginning of this blog, what exactly was Amphicyon? A bear or a dog? Well the answer is in fact neither. Amphicyon belonged to a family known as the Amphicyonidae, which included it and all other species of Bear-Dogs. This family belonged to an order known as the Caniformia, which also contains the dog and bear families as well as foxes and sea lions. As a result Amphicyon and its kin were actually close cousins of bears and dogs, separating from them in the evolutionary tree around 40 million years ago during the Eocene period. The Bear-Dogs evolved into a wide range of shapes and sizes, filling a variety of niches. However, despite its success, Amphicyon and its kin would sadly go extinct around 7.2 million years ago. The main cause of this was the changing environment at the end of the Miocene. The climate became dryer, which resulted in the emergence of more open plains. This meant that the slower, bulkier Amphicyon could not find the cover it needed to ambush its prey. This meant that they struggled to find enough food to support their large size. Also (rather ironically) another factor was the emergence and success of the dogs and bears. Dogs were more specialised in the endurance hunting style that is effective on open plains, and some had jaws that could crush bone, something Amphicyon couldn’t do despite its impressive appearance! (In fact one group of dogs, named the Borophaginae, are commonly referred to as the “bone-crushing dogs”!) Bears meanwhile had a more omnivorous diet than Amphicyon, giving them access to a wider range of food. Dogs and Bears were also generally smaller, so didn’t require as much food to keep them alive. In addition at about this time the first Sabre-Tooth Cats were evolving, bringing yet more competition. These three groups together took over all the niches that had previously been occupied by Amphicyon and its relatives. As a result this magnificent group of animals were squeezed out and confined to the pages of pre-history.
It’s a shame too, as a pet Amphicyon would have been not only a cute puppy but also grown to be an effective “guard dog”. It would certainly draw more than a few glances when you took it for a walk!
Antunes, Miguel. Telles, Balbino, Ausenda C., Ginsberg, Léonard. Ichnological evidence of a Miocene rhinoceros bitten by a bear-dog (Amphicyon giganteus), Annales de Paléontologie, Volume 92, Issue 1, 2006, Pages 31-39,
Morse, Paul E. “Amphicyon longiramus” Florida Museum, Oct. 5, 2012, floridamuseum.ufl.edu/florida-vertebrate-fossils/species/amphicyon-longiramus/
Sorkin, Boris. (2006). Ecomorphology of the giant bear-dogs Amphicyon and Ischyrocyon. Historical Biology. 18. 10.1080/08912960600618073.
Qigao Jiangzuo, Chunxiao Li, Shiqi Wang & Danhui Sun (2018) Amphicyon zhanxiangi, sp. nov., a new amphicyonid (Mammalia, Carnivora) from northern China, Journal of Vertebrate Paleontology, 38:6, DOI: 10.1080/02724634.2018.1539857