Megalosaurus (Gr. , great, and , lizard), a gigantic fossil reptile of the family of dinosaurians, which includes the iguanodon, previously described. This family, entirely extinct, was remarkable for great size and for certain mammalian characters; the long bones have a medullary cavity, the feet are short and pachyderm-like, the sacrum composed of at least five anchylosed vertebrae, the ribs doubly articulated to the spine, the vertebral laminae greatly developed, and the lower jaw capable of a horizontal triturating motion; but the teeth, scapular arch, and most of the skeleton resemble those of lizards. The genus megalosaurus (Buckland) was discovered by Dr. Buck-land in the Stonesfield oolite near Oxford, Eng.; remains have also been found in the Wealden and Jurassic formations. The if. Buchlandi(Cuv.), the best known species, had probably a straight muzzle, thin, and laterally compressed; the teeth were flat, pointed, curved backward like a pruning knife, with the enamel of the posterior edge serrated to the base, and for a short distance from the point also on the anterior; the structure of these teeth, calculated to lacerate flesh and to hold a prey once seized, shows that the animal was highly carnivorous.
The teeth, some of them 3 in. long, were implanted in distinct sockets formed by partitions running across from the higher external to the lower internal border of the jaw, combining crocodilian and lizard characters. This animal must have attained a length of 30 or 40 ft.; it was terrestrial, and probably preyed upon the smaller reptiles and the young of the larger. - The hylceosaurus (Mantell), another dinosau-rian reptile, is described under its own head.