Fig. 98.–Skull of Anchisaurus coelurus. × ¼. (After Marsh.) a, Nasal fossa; b, antorbital, c, infra-temporal, d, supra-temporal, and o, orbital fossa; q, quadrate bone.
Megalosaurus, from the Trias to the Wealden in England and France, with other species in Colorado and India, reached a considerable size, larger than that of any other Theropoda, the scapula of M. bucklandi being nearly three feet long, and the femur still longer. The hind-limbs are twice as long as the fore-limbs. The cervical vertebrae are short, the neck being much shorter than the tail. Hands with five fingers, feet with four toes. Pubic bones long and slender, with a broad symphysis. With well-developed abdominal ribs, resembling those of crocodiles.
Allosaurus, from the Upper Jurassic of North America, with only three toes. Ischia and pubes united into one symphysis. Anterior extremities very short. Sacrum consisting of four vertebrae. Total length of some of the larger species about twenty feet.
Fig. 99.–Skeleton (× 1⁄40) and skull of Ceratosaurus nasicornis. (After Marsh.) a, Nasal cavity; b, bony horn-supporting excrescence; c, pre-orbital fossa; d, orbital fossa.
Ceratosaurus nasicornis, from the Upper Jurassic of Colorado, is about seventeen feet long. The generic and specific names refer to the nasal bones, which are raised into an unpaired longitudinal crest. This, by its rough surface, suggests that it was covered by a horny sheath, or carried a horn. The large skull, about two feet in length, is armed with strong, slightly curved, laterally compressed, sharp teeth, unequal in size. The pre-orbital foramen is large, bordered above by the prefrontals, which are raised into prominent knobs. The supratemporal foramina are extremely small, the lateral foramina very large. The quadrate slants backwards. The sacrum consists of five vertebrae. The caudal vertebrae carry long and slender chevron-bones. The pubes and ischia are long and slender, each forming a separate symphysis at their broadened ends. The three metatarsals are elongated and fused with each other. There seems to have been some dermal armour in the shape of osseous plates, which extended in one series from the occiput over the neck.
Coelurus gracilis, of the Upper Jurassic of Wyoming, and closely allied forms in the Wealden of England, are remarkable for the pneumaticity of the centra and processes of their vertebrae, the bony parts of which are restricted to thin, hollowed-out shells, so that the whole skeleton must have been very light. Computed length of these imperfectly preserved creatures about five feet.
Hallopus victor, of the Upper Jurassic of Colorado. Anterior extremities very short, with only four fingers; posterior limbs very long and slender, especially the tibia; the much elongated metatarsals are separate, the first absent, the fifth much reduced, so that the foot is tridactyle; the calcaneum projects like a heel. The ilium is attached to two sacral vertebrae only; the pubes are slender, forming a narrow symphysis, while that of the ischia is broad. Most of the bones of this creature, which probably progressed by hops, are hollow. Total length about three feet, the length of the hind-limbs being about nine inches.
Compsognathus longipes, of the Upper Jurassic of Bavaria, is one of the smallest of all the Dinosaurs. It is most remarkable on account of its almost bird-like feet. The fibula is much thinner and somewhat shorter than the tibia; the latter is closely attached to, although not fused with the proximal tarsal bones, while the distal tarsals are fused with the united and much elongated second, third, and fourth metatarsals; the fifth is reduced to a short bone near the intertarsal joint; while the first is represented by its distal portion only, which is stowed away on the hinder aspect of the middle of the second metatarsal, and carries two phalanges. The three middle toes consist of three, four, and four phalanges respectively. Whilst the whole hind-limb is typically avian, the pelvis is quite different; the pubic bones are simple, slender, and directed forwards, forming a symphysis with their whole distal halves, and broadening out distally into a horizontal process directed towards the symphysis, which is likewise formed by the fusion of the inner surfaces of the thin and rather flat ischia. The fore-limbs are only half the size of the hind-limbs. The neck consists of about ten vertebrae, mostly with long and pointed ribs. Tail long with well-developed chevrons. The skull is long and pointed, composed of thin bones, which have lost most of the sutures; with large lateral, temporal, and pre-orbital, but without supratemporal, foramina. Premaxillae, maxillae, and mandible with numerous slender and rather long, conical, alveolar teeth.
Order III. ORTHOPODA