Hylaeosaurus

Phylogeny: Dinosauria > Ornithischia > Genasauria > Thyreophora > Thyreophoroidea > Eurypoda > Ankylosauria > Euankylosauria > Nodosauridae (?)

Overview: The renowned English naturalist Sir Richard Owen used three genera to establish the Dinosauria as a taxonomic clade - Megalosaurus, Iguanodon and Hylaeosaurus. The former two are relatively well known, but Hylaeosaurus is notably more obscure. Fossils of the animal, which make up a portion of its body and dermal armor, were first discovered in the 1830’s. They originated from a quarry in the southeast of England, in what is now Tilgate Forest. Said remains were obtained by Gideon Mantell, who had previously named and described Iguanodon. Mantell would do the same for Hylaeosaurus in 1833, naming in reference to where it was found. Along with Megalosaurus, Iguanodon and many other prehistoric animals, a statue of Hylaeosaurus would be erected in London’s Crystal Palace Park in the 1850’s. There, it was depicted as a large, lizard-like creature with a line of spines running down its back.

Nowadays, we know that the spines on Hylaeosaurus were arranged somewhat differently. It was an ankylosaur, meaning it had dermal armor formed out of many different rows of osteoderms - bony lumps growing within its skin. These protected its back, sides, neck, tail and head. Some were flatter, smaller and oval-shaped, others were long and spiked. Ankylosaurs were, in general, low-slung herbivores that fed upon ground-level vegetation like ferns. Size-wise, Hylaeosaurus was on the low to average end. Ankylosaurs tend to be split into two major families - the typically clubless Nodosauridae and the usually club-tailed Ankylosauridae. Traditionally, Hylaeosaurus has been seen as a nodosaurid, possibly closely related to a genus called Polacanthus. Recent studies have instead suggested it could’ve been a basal ankylosaurid. Others suggest Hylaeosaurus could’ve been an ankylosaur belonging outside either family.