Each side of the snout had five sinuses, four of which expanded into the maxilla bone. These extra sinuses and nasal chambers in the snout may have been for heat and water balance or may have played a role in vocalization.

In 1906, an American Museum of Natural History expedition led by American paleontologist Barnum Brown discovered the type specimen of Ankylosaurus magniventris (AMNH 5895) in the Hell Creek Formation, near Gilbert Creek, Montana. The specimen consisted of the upper part of a skull, two teeth, part of the shoulder girdle, cervical, dorsal, and caudal vertebrae, ribs, and more than thirty osteoderms.

A handful of specimens have been excavated to date, but a complete skeleton has not yet been discovered.