Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other marine mammals, such as seals and sea cows, due to convergent evolution. However, they evolved from originally terrestrial mammals. The most likely ancestors were long thought to be mesonychids—large, carnivorous animals from the early Cenozoic (Paleocene and Eocene), which had hooves instead of claws on their feet. Their molars were adapted to a carnivorous diet, resembling the teeth in modern toothed whales, and, unlike other mammals, have a uniform construction.