They were herbivorous ornithischian obligate quadrupeds, meaning that they were not able to walk using only their hind legs. They first appeared at a time when the Stegosaurs were dying out, and some paleontologists believe that they may have been descendents of the Stegosaurs. They were heavily built, medium-sized dinosaurs about 6.5 to 26 feet (2 to 8 meters) in length. Their bodies were low and broad, with short, powerful legs.
The Nodosaurs (Family Nodosauridae) first appeared in the mid or late Jurassic Period (195 to 140 million years ago) in Europe, they then spread to Asia and North America, and a few species spread into South America, Africa, and Australia. They went extinct during the late Cretaceous Period (140 to 65 million years ago). Their name means "nodular or lumpy reptile."
The Nodosaurs had narrow, pear-shaped skuls that were longer than they were wide. They were herbivores with toothless horny beaks, and leaf-shaped teeth in their cheeks. They had solid bony plates that covered their bodies from their necks to their tails, and long spikes along the sides of their bodies and over their pectoral girdles which protected their flanks. Unlike the Ankylosaurs and the Stegosaurs, they did not have have clubbed or spiked tails.
The first known Nodosaur was Hylaeosaurus, whose name means "woodland reptile". Hylaeosaurus was first discovered in the Tilgate Forest area of Sussex, England. It was first described in 1832 by Gideon Mantell, and later by Sir Richard Owen. Hylaeosaurus lived during the early Cretaceous Period in Europe. The skeleton is in the collections of the British Museum of Natural History, and has yet to be fully prepared.
Another early Nodosaur was Polacanthus, whose name means "many spikes." Polacanthus was discovered in 1865 by the Rev. William Fox; it was a contemporary of Hylaeosaurus, meaning that it lived at the same time and in the same range. The skeleton of Hylaeosaurus consists of the front part of the animal, and the skeleton of Polacanthus consists of the back part of the animal without any overlap between the bodies, leaving some paleontologists to believe that they may actually be the same species.
Nodosaurus ("nodular reptile") was first mentioned as a species by O. C. Marsh in 1889, but was not described until 1921 by Richard Lull. Nodosaurus lived during the late Cretaceous Period in North America, its remains have been found in Kansas and Wyoming. More of its skeleton is known than other species of Nodosaur, and it is considered to be a typical Nodosaur; the Family Nodosauridae name is derived from this species.
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