Hylaeosaurus is the most obscure of the three animals used by Sir Richard Owen to first the new group Dinosauria, in 1842. The first Hylaeosaurus remains to be found were dug up by Gideon Mantell in 1832.
Gideon Mantell originally estimated that Hylaeosaurus was about 7.6 m long, or about half the size of the other two original dinosaurs, Iguanodon and Megalosaurus. Modern estimates range up to 6 metres in length.
Name: Hylaeosaurus, meaning ‘woodland reptile’
Size: 4m long
Lived: about 130 million years ago in the Early Cretaceous Period in southern England
The fossils are entombed in a slab of limestone that can still be seen in London’s British Museum. Perhaps out of respect for the first generation of palaeontologists, no one has taken the trouble to actually prepare the fossil specimen, which seems to have been left by a dinosaur closely related to Polacanthus.
Only the front part of the dinosaur was found. Palaeontologists had to guess how the legs and body armour looked, but they are pretty certain that it looked like a long lizard with a cloak of sharply spiked armour running from its neck right down to the tip of its tail.
Hylaeosaurus was a slow-moving herbivore that nibbled ferns and other green plants for its food. If it was attacked, Hylaeosaurus was protected by its heavy armour and intimidating spikes.
It was a fairly typical nodosaur, with three long spines on its shoulder, two at the hips, and three rows of armour running down its back. It may also have had a row of plates down its tail. It had a long head, more like the head of a Nodosaurus than an Ankylosaurus and a beak, which it probably used to crop low-lying vegetation.