Epicyon haydeni

It makes sense that the largest canid ever known to have existed doesn’t have a common name, as there is very little about this creature that is common. Archaeological evidence suggests this animal lived from the middle to late Miocene epoch, between 12 and 6 million years ago.

Scientific Classification and Name

Epicyon haydeni belongs to the Canidae subfamily Borophaginae; in other words, this subfamily is reserved for “bone-crushing dogs.” Species in this subfamily are extinct, and they were endemic to North America. The genus name, Epicyon, means “more than a dog.”

Paleontologist Joseph Leidy chose the species name, haydeni, to honor Dr. Ferdinand Vandeveer Hayden, a geologist who collected the type specimen of the species while a member of the 1856-1857 Warren surveying expedition. Leidy first identified it as a subgenus of Canis in 1858, but later examinations of the species led to a number of changes to its genus classification.

In 1980, paleontologist Jon Baskin recombined it as Epicyon haydeni, and the classification has stuck. Alternate species names over the years have included the following:

• Aelurodon haydeni
• Aelurodon haydeni validus
• Aelurodon aphobus
• Aelurodon mortifer
• Canis haydeni
• Epicyon validus
• Osteoborus validus
• Osteoborus ricardoensis
• Tephrocyon mortifer
• Tomarctus mortifer

Description and Size

The largest individuals of Epicyon haydeni were about the size of a grizzly bear. The height of its shoulder reached as tall as 35 inches, its body length averaged 7-10 feet, and it weighed 200-300 pounds with the largest known specimen weighing 370 pounds. These canids surpassed the size of modern-day wolves.

This canid creature is often compared with hyenas because they several physical attributes concerning their skulls and mouth: a widened palate, shorter rostrum, and dome-shaped forehead. However, hyenas are not members of the Canidae family.

These canids had a small clavicle and flexible limbs. Based on their legs and the body proportions of the fossils, scientists believe they were probably less cursorial; that is, they could not run fast and for long distances. Instead, they likely ran in short, speedy bursts.

Habitat and Range

Epicyon haydeni fossils have been found across a vast swath of North America, including the U.S. states of Arizona, California, Colorado, Florida, Idaho, Kansas, Montana, Nebraska, New Mexico, Oklahoma, Oregon, and Texas, and in the province of Alberta in Canada.

During the Miocene epoch, open grasslands with scattered trees, a warm climate, and seasonal variations characterized the geographic range where fossils of Epicyon haydeni have been found. These lands are known for having been grazed by herbivorous animals.

Diet

This creature’s teeth reveal that it likely had a hypercarnivorous, bone-crushing diet. “Many teeth of Epicyon haydeni show signs of very heavy wear, which has also been interpreted to be evidence of dental erosion caused by bone-crushing (Munthe, 1989),” according to the Florida Museum of Natural History. 

Their prey likely consisted of now-extinct animals known to have lived within the range of Epicyon haydeni: camel relatives from the genus Aepycamelus, deer species belonging to the genus Cosoryx, horse-like animals in the genus Neohipparion, Prosthennops (a warthog species), and ancient rhinoceroses from the genus Teleoceras.

However, what these canids ate is based on analyses of Epicyon haydeni’s habitat and teeth, along with some speculation.

Threats and Extinction

As an apex predator, Epicyon haydeni likely did not have many predators. However, this animal did share territory with a number of other large apex predator species, including giant bears belonging to the extinct genus Agriotherium, the feliform Barbourofelis, the machairodont cat Amphimachairodus coloradensis (also known as the saber-toothed tiger), and a fellow canid Borophagus. All of these animals could have presented competition for resources and could have preyed on Epicyon haydeni.

Its extinction is thought to have resulted from competition from big cats that could run fast and for long distances—something Epicyon haydeni‘s anatomy suggests they were not able to do.

It is thought that these dogs went extinct due to the emergence of the big cats, most notably the saber-toothed tiger. These animals are understood to have preyed on the same animals that Epicyon haydeni did, thereby (possibly) starving the world’s largest canid. This decline in nutrition would have made breeding difficult and increased pup mortality.