Possible Identification-Hylaeosaurus armatus? Name Meaning: Belonging to the Forest

Talas Location Found: Wealden Supergroup, Hastings Beds, England

Maseru Geologic Era: Early Cretaceous

Estimated Range: England, with possible remains also found in Germany

Size: 5 meters long

Extinction: 136 million years ago

These are pieces of dermal armor from an armored dinosaur. Both are probably parts of a spike. The only confirmed thyreophoran (armored dinosaur) that I could find coming out of this formation is Hylaeosaurus, a small to mid sized basal ankylosaur. In life, Hylaeosaurus had a series of spikes of varying sizes that ran along its side, as well as smaller, bump like spikes on its back. Our specimen is probably one of the dorsal, more knob-like spikes. Both kinds of bone, both cancellous and compact, are visible in the specimen. The second bone is a fragment of an armor spike from the same type of animal.

Hylaeosaurus has the distinction of being one of the first three dinosaurs named. Unlike the other two (Iguanodon and Megalosaurus), Hyaelosaurus did not become a wastebasket taxon, though the majority of its skeleton is still unknown. Debate still exists as to which group Hylaeosaurus belongs in. Some place Hylaeosaurus in the nodosaurid group, others with the polacanthids, and still others group it as an ankylosaur. This debate might be settled someday if more of the skeleton is recovered. Even a reasonably complete skull in decent condition could at least narrow the groups down.

What all of these groups have in common is dermal armor, ranging from bony plates on the back to spikes on the side and club-like tails. Given how early in the history of ankylosaurs Hyaelosaurus appeared, it most likely did not have a club on the end of its tail. That being said, a complete tail has not yet been recovered, so this idea could change in light of new material.

Gargoyleosaurus-a related animal

Hylaeosaurus would have been a fairly typical armored dinosaur. It certainly was not the largest of this group, but thyreophorans could make up for this in the amount of bone and spikes piled on their backs. Even without a tail club, that amount of protective bone would have make Hylaeosaurus a rather undesirable prey item for the predators in the area. All an animal like Hylaeosaurus would have to do is hunker down and wait for the predator to either lose interest or exhaust itself beating its head on the armored back. A few broken teeth would probably persuade most predators that Hylaeosaurus was not worth the trouble.

Image Credits:

Full Skeleton: By Zach Tirrell from Plymouth, USA – Camarasaurus, CC BY-SA 2.0,

Life Restoration: