Henodus was a three-foot-long (one-meter-long) marine reptile called a placodont that crushed bottom-dwelling shellfish with two upper teeth at the back of its beaklike snout. The snout was squared off just in front of the eyes, making the head unusually boxy. The ancient placodont looked like a flattened turtle, though its protective shell of bony plates was twice as wide as long and relatively flat.
Four paddle-like limbs and a short tail allowed Henodus to skulk along the floor of shallow, brackish lagoons in Europe during the late Triassic period, about 228 million to 200 million years ago. Its weak limbs likely made walking on land difficult; nevertheless Henodus was an air breather and probably amphibious—returning to the shore to rest, breed, and perhaps seek refuge from aquatic predators.