These animals had a tail club and are related to the nodosaurid dinosaurs like Nodosaurus. Ankylosaurids were vegetarians that walked on all-fours and had heavy armored bodies. Some had bands of armored plates across the back and tail, and may also have had bony plates projecting up from back and shoulders. Ankylosaurids had reinforced skulls with bony horns and a wide beak lacking teeth. The tail of these dinosaurs was stiffened near its tip by bony tendons, and ended in a bony club. Ankylosaurids measured from 18-35ft long and lived from the Early to Late Cretaceous periods, although Scelidosaurus, which lived in the Early Jurassic period may be an ancestor of the ankylosaurids.

Scelidosaurus means 'ribbed lizard', and it gets its name from the large number of ribs of this animal that have been excavated. Scelidosaurus was a 13ft long Early Jurassic dinosaur found in Arizona, England, Portugal, and Tibet. Scelidosaurus had four stout legs and a body armored with bony knobs and spikes.

Ankylosaurus means 'stiffened reptile', Ankylosaurus was the largest ankylosaurid dinosaur and was up to 35ft long. It had an armored head and a horny beak, and its back was covered with bony plates from which spines projected. Ankylosaurus also had heavy-set limbs to support its huge weight, and had a massive tail club some 16 inches wide for protection. This dinosaur lived in the Late Cretaceous period and remains have been found in Alberta, Canada and Montana, USA where fairly complete material has been found.