Heavier than an average gorilla and similar in length to a Komodo dragon, Hayden’s bone-crushing dog (Epicyon haydeni) was the largest dog species ever.
The colossal canine existed for about 15 million years during the mid-late Miocene epoch, going extinct 5.3 million years ago.
Native to North America, fossils have been found in 12 US States ranging from Florida to California, in addition to Alberta, Canada.
Its body was estimated to be 2.4 metres (7.9 ft) long, with a shoulder height of 90 cm (35 in) and an average body mass of 100–125 kg (220–276 lb). The largest known specimen is estimated to have weighed up to 170 kg (370 lb).
The species belongs to the Epicyon ("more than a dog") genus, which belongs to the subfamily Borophaginae ("bone-crushing dogs").
With skulls resembling lions more so than wolves, all Epicyon had huge heads and strong jaws adapted for bone crushing, allowing them to scavenge the skeletons of dead animals as well as hunt.
This access to nutritious bone marrow was something that other carnivores of the time did not have.
Additionally, all Epicyon had grindstone-like molars for eating plants and insects.
Due to its bigger size and heavier skeleton, Epicyon haydeni was unable to run as long a distance as others such as Epicyon saevus, which was half as heavy and almost half as tall.
Instead, Epicyon haydeni relied on social hunting strategies and short bursts of speed.
Based on analysis of fossilized faeces, it is believed to have had a digestive tract similar to modern-day hyenas due to its ability to break down large amounts of bone.
Its prey included now-extinct species of camel, horse, pronghorn and rhinoceros, whether it be through scavenging or hunting.
It competed against – and potentially conflicted with – other predators for food and territory. For example, in Texas, the land was home to now-extinct species of bear, wild cat and fellow bone-crushing dogs.
No present-day dog breeds can match up to Hayden’s bone-crushing dog in terms of overall size and weight, although some have come close: the longest dog ever and heaviest dog ever (before we stopped monitoring the record due to animal welfare concerns) was an Old English mastiff named Zorba, who was 2.5 metres (8.3 ft) long and weighed 155.5 kg (343 lb) in 1989.
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