AMPHICYON: THE MIOCENE’S ALL-TERRAIN PREDATOR
In 1960, at a time when little was known about the anatomy and body proportions of bear-dogs, American paleontologist Stanley Olsen described a wonderful collection of postcraneal fossils of Amphicyon longiramus, from the Miocene site of Thomas Farm in Florida. Olsen’s paper profiled a kind of predator with no living counterpart. With a body size comparable to that of a modern brown bear, Amphicyon had a longer and more flexible back and a long, heavy tail. Its dentition resembled that of a dog more than that of a bear, and was better suited for consuming meat and bone, while still allowing the animal a varied diet.
In the middle Miocene, when sabertooth cats hadn’t yet attained their full size and dominance, amphicyonine bear-dogs like Amphicyon were the undisputed ruling predators, both in Eurasia and in North America. Although they could not run especially fast or long, they were capable of ambushing large animals using a vaguely cat-like hunting style, and then they could use their great muscular strength and powerful canine teeth to bring down and kill their prey. But with the late Miocene the rule of the bear-dogs was challenged by the appearance of such powerful felid sabertooths as Machairodus. Later relatives of Amphicyon, such as Magericyon, (best known thanks to the fossil sample from Batallones in Spain)adapted to the new times by becoming somewhat smaller and developing more specialized dentitions for killing and consuming large prey efficiently. But there was no resisting the empire of the machairodonts, and near the end of the Miocene the bear-dogs disappeared for good after many million years of successful evolution.
Here is the reference of Olsen’s papers:
Olsen, Stanley J. 1960. The fossil carnivore Amphicyon longiramus from the Thomas Farm Miocene. Part II, Part II. Cambridge, Mass: Harvard University, Museum of Comparative Zoology.