Ophiacodon had a skull with a deep, narrow shape. This shape meant that it could have long and every strong jaw muscles. It's back legs were longer than its front legs so it was probably a good runner, even though it was much larger than the earlier pelycosaurs. It weighed between 66lb and 110lb (30kg and 50kg). To take the weight off its feet, it is likely that Ophiacodon spent some of its time in shallow water. There it scuttled about in floodplains or swamps, catching fish and amphibians in its jaws, and killing them with its sharp teeth.