|Cast of Ankylosaurus skull (AMNH 5214) in front view, Museum of the Rockies|
The body was broad and low-slung and covered in armour. Carnivores, attacking from above, would find no weak points, and the animal could defend itself by using its clubbed tail.
The most obvious feature of Ankylosaurus is its armour, consisting of massive knobs and plates of bone, known as osteoderms or bony scutes, embedded in the skin. Osteoderms are also found in the skin of crocodiles, armadillos and some lizards. The bone was probably overlain by a tough, horny layer of keratin.
These osteoderms ranged greatly in size, from wide, flat plates to small, round nodules. The plates were aligned in regular horizontal rows down the animal's neck, back, and hips, with the many smaller nodules protecting the areas between the large plates. Smaller plates may have been arranged on the limbs and tail. Compared to the slightly more ancient ankylosaurid Euoplocephalus, the plates of Ankylosaurus were smooth in texture, without the high keels found on the armor of the contemporaneous nodosaurid Edmontonia. A row of flat, triangular spikes may have protruded laterally along each side of the tail. Tough, rounded scales protected the top of the skull, while four large pyramidal horns projected outwards from its rear corners.
Underneath it was covered by normal skin, but to get at it the carnivore would have to turn over an animal weighing up to 6,000 kg (11,000 lb).
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- Carpenter K. 2004. Redescription of Ankylosaurus magniventris Brown 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America. Canadian Journal of Earth Sciences, 41: 961–986.