Eryops was a temnospondyl (large and very ancient amphibian) averaging 1.5-2.0 m (5-6 ft) in length whose name means “drawn out face.” It lived during the Permian period, about 295 million years ago, and most fossils are found in the Admiral Formation of Archer County, Texas. Eryops is thought to have been one of the largest land animals of its time, as land animals themselves had only evolved from fish about 40 million years prior. One of the only larger animals living at the time was the cow-sized, sailbacked Dimetrodon, which probably hunted Eryops. Eryops lived at least 70 million years before the dinosaurs.
Eryops is the most famous Paleozoic amphibian and an interesting example of natural engineering. Having evolved from lobe-finned fish, Eryops retained many fish-like characteristics but adapted them for land life. Like some fish, Eryops had a gaping maw and a large head relative to its body. The head as much as two feet long, pretty impressive for an animal that is only about 5 feet long itself. In fact, the primary Eryops species is named Eryops megacephalus, meaning “big head.” Like other amphibians, Eryops was a swamp-dweller.
Being little more than a fish with cursory adaptations for land life, Eryops used most of its walking strength just keeping its body off the ground. This was a slow and difficult chore, accomplishing with strong, sprawling limbs. Its short, broad strides are preserved as fossilized footprints. Erect limbs would not evolve in animals until tens of millions of years later.
Eryops ate fish, small reptiles and amphibians, and the numerous invertebrates, such as insects, available in a terrestrial world with barely any predatory tetrapods. Like modern crocodiles, Eryops was a stealth hunter – it couldn’t hunt any other way, being very slow – and probably sat quietly in the water with only its eyes and nostrils visible. It had a short tail, suggesting it also lacked the ability to move quickly in the water, and could only have existed in a world where the terrestrial carnivore niche had just begun to be exploited.