The type material for Hylaeosaurus is a confusing looking muddle of bones. Aside from the fact that the term dinosaur was not in existence at the time these were described, this jumble of very alien appearing bones was probably both confusing and somewhat alarming to Mantell and the scientific community and led to their description as saurian at best. This jumbled up fossil used as the type specimen gives both very little and a great deal of information. There is very little overall information of the entire animal presented here. The material is from the anterior aspect of the vertebral column, near
to the head. These armored spikes led Mantell to add the specific
epithet armatus meaning armored. There is, however, quite a deal of information in the fossil that allowed Mantell to describe a new animal that became 1/3 of the basis of Owen's description of dinosaurs.