Hylaeosaurus (Greek for "forest lizard"); pronounced HIGH-lay-oh-SORE-us
Woodlands of western Europe
Early Cretaceous (135 million years ago)
Size and Weight:
About 20 feet long and 1,000-2,000 pounds
Spines on shoulders; armored back
We know much more about Hylaeosaurus' place in paleontological history than we do about how this dinosaur actually lived, or even what it looked like. This early Cretaceous ankylosaur was named by the pioneering naturalist Gideon Mantell in 1833, and almost a decade later, it was one of the handful of ancient reptiles (the other two were Iguanodon and Megalosaurus) to which Richard Owen assigned the new name "dinosaur."
Oddly enough, the fossil of Hylaeosaurus is still exactly as Mantell found it--encased in a block of limestone, at the London Museum of Natural History. Perhaps out of respect for the first generation of paleontologists, no one has taken the trouble to actually prepare the fossil specimen, which (for what it's worth) seems to have been left by a dinosaur closely related to Polacanthus.