Seen at the Petrified Forest National Park’s visitor’s center in Arizona, it’s Desmatosuchus spurensis — and like all Aetosaurs, it was an odd looking thing:
Aetosaurs were an order of reptiles that lived in the Late Triassic, about 200 – 230 million years ago. Aetosaur comes from the Greek for “eagle lizard,” since their skulls somewhat resemble those of birds — but they had pig-like snouts (for rooting), a body much like those of crocodiles, and armored plates on their backs like those of modern-day armadillos. So picture an armored crocodile with a bird-like head and a pig-like snout, and you’ve got a good idea of what an odd sort of creature an aetosaur was.
Desmatosuchus was one of the largest aetosaurs, about 5 meters (16 feet) long, and standing about 1.5 meters (5 feet) high. It had the additional feature (unlike most other aetosaurs) of two rows of spikes along the sides of its back — one over each shoulder. The spikes grew some 45 centimeters (18 inches) long, definitely useful for discouraging predators.
BTW, aetosaurs star in an interesting bit of paleontological history — written up nicely here.