It was discovered in 1832 by Gideon Mantell. In 1842 it was one of the three dinosaurs Richard Owen based the Dinosauria on. Only limited remains have been found of Hylaeosaurus and much of its anatomy is unknown. A recent cladistic analysis sees it as a basal ankylosaurid.
Hylaeosaurus was about five metres long. It was an armoured dinosaur that carried at least three long spines on its shoulder.
- Arbour, Victoria M; Zanno, Lindsay E; Gates, Terry (2016). "Ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation, sea-level fluctuation, and geodispersal". Palaeogeography, Palaeoclimatology, Palaeoecology. 449: 289–299. Bibcode:2016PPP...449..289A. doi:10.1016/j.palaeo.2016.02.033.