Mesonychids were large carnivorous mammals related to ungulates and cetaceans that lived in the Paleogene, resembling wolves but with hooves and larger heads. They were the largest carnivores in North America and had tremendous biting power. Some were adapted for hunting fish, while others had a scavenger lifestyle. They are thought to be descended from condylartes and were once thought to be the ancestors of whales.
Mesonychids are medium-large carnivorous mammals closely related to ungulates (pigs, camels, goats, cattle) and cetaceans (whales and dolphins) that lived in the Paleogene, evolving immediately after the extinction of the dinosaurs 65 million years ago and became extinct about 30 million years ago. Mesonychids bore a superficial resemblance to wolves, although they had hooves instead of paws and much larger heads. They were also larger overall, with some species exceeding the size of bears. In North America, mesonychids have been the largest carnivores for millions of years.
Mesonychids were typically larger than the other two groups of carnivores they shared the planet with at the time: miacids (which evolved into modern carnivores) and creodonts, another carnivorous group as mesonychids were once classified. Mesonychids are native to Asia (which was an island continent) and rapidly spread across much of the Northern Hemisphere, including Europe (which was an archipelago at the time) and North America (which was separate from South America from the ocean).
Although mesonychids have similar skulls to canids, the two are quite different. Mesonychids had longer, flatter skulls and an exaggerated sagittal crest, a cranial crest that would have been used as an anchor for jaw muscles. The large sagittal crests of mesonychids indicate that they would have had tremendous biting power, with some species being more powerful than any living carnivore. Mesonychid canines were slightly longer and thinner than canids, better at piercing flesh but slightly worse at holding the kill.
Mesonychids had triple-pointed mandibles, suggesting that some of them were adapted for hunting fish, like their relatives the toothed whales. Male mesonychids had thick carnassals that would have been useful for crushing bones, indicating a scavenger lifestyle. Evolutionarily, mesonychids are thought to be descended from condylartes, the earliest hoofed animals. Whales, which are mammals, were thought for many years to be descended from mesonychids, but more recent fossil finds make it seem more likely that they descended from hippopotamus ancestors.
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