Laosaurus of Colorado is a smaller form, intermediate in structure between the former genus and Hypsilophodon foxi from the Wealden of the Isle of Wight. A small creature, less than 5 feet in length. Four fingers, with 2, 3, 4, 2 phalanges; fifth metacarpal vestigial. Four toes with 2, 3, 4, 5 phalanges and long claws. Astragalus and calcaneum separate. Post-pubis very slender. Each premaxillary with five pointed alveolar teeth, leaving a wide median diastema; maxillaries with eleven, dentaries with ten laterally compressed blade-like teeth.
Iguanodon from the Wealden of England, Belgium, and Germany. Apparently two species, I. mantelli, about 16 feet, I. bernissartensis nearly 30 feet long. The premaxilla is quite toothless; the teeth of the maxillae and mandibles stand in close series, implanted in alveolae; they are spatulate, laterally compressed, with finely serrated edges, and slightly curved, the lower outwards, the upper inwards, and bear a general resemblance to those of Iguana, hence the generic name. There is only one functional set of teeth, and these are much worn down by use, but in such a way that, owing to the different curvature of the opposed teeth, the worn-down crowns form cutting, and at the same time crushing, almost triturating surfaces, indicating that these animals lived upon herbs. The gait of these creatures was upright, as shown by their spoors; the long almost vertical ischia, which form a padded symphysis, only slightly raised above the ground, suggest that this symphysis was used as a true sitting support, the animal resting upon it, the hind-limbs and the long tail. The latter, to judge from the long chevrons and the high neural spinous processes, must have been furnished with strong muscles. The whole tail was undoubtedly used as a balance during the upright position. Many of the tendons of the dorsal spinal muscles on the back and upper half of the tail are ossified. The post-pubic branches are very slender, distally much reduced, and, except at the obturator-foramen, separated from the ischia; the pre-pubes are very strong and broad. The femur has a fourth trochanter, a feature which induced the unfortunate late Paul Albrecht to declare that Iguanodon was a reptilian Duck! The tarsal bones are separate. The metatarsals and toes are reduced to three, with 3, 4, 5 phalanges respectively, the first being a mere styliform vestige. The anterior limbs are likewise very powerful, but are much shorter; the hands are adapted for grasping, possibly for defence and offence, as indicated by the pollex, which, although short, is transformed into a formidable spur-like weapon, firmly fixed at a right angle to the other four fingers, the phalanges of which number 3, 3, 3, 4; the second and third fingers were protected by hoof-like nails, the fifth finger is feeble, and stands somewhat apart. The whole vertebral column consists of more than eighty vertebrae, of which ten are cervical, eighteen thoracic and lumbar, while five or six are fused into the sacrum. The cervical vertebrae are opisthocoelous, and carry short ribs, except the atlas, which possesses two separate supra-dorsal pieces, which fill the gap between it and the occiput.
Fig. 101.–Skeleton of Iguanodon bernissartensis. × 1⁄80. (After Marsh.)
Many specimens of I. bernissartensis, which is now completely known, including even the hyoid bones, were discovered in 1878, in the Belgian colliery of Bernissart, between Mons and Tournai, close to the French frontier. The bones were in a fault or crack, filled with clay of Wealden age, about one thousand feet below the present sea-level, and there about thirty Iguanodons, all apparently adult, had become embedded. Five of them are now mounted in one of the public galleries of the Brussels Museum, of which these perfect monsters form one of the chief attractions. Having proved to be such a valuable find, they were claimed by the Government, on the ground that Iguanodons were not included in the license of the Coal Mining Company. The fact that not only I. bernissartensis, but also a few specimens of I. mantelli, already known from England, where the large form likewise occurs, were found in the same place, makes the specific differences somewhat doubtful; they are perhaps sexual.
Claosaurus of the uppermost Cretaceous strata of Wyoming, is one of the latest of Dinosaurs. It is nearly allied to Iguanodon, but has only three functional fingers, the fifth being absent, whilst the pollex is very short.
Hadrosaurus s. Diclonius of the same level as the preceding genus in North America, apparently also in the Middle and Upper Chalk of England and Belgium, has a most peculiar spoon-shaped bill, the premaxilla and the predental bone being spatulate and quite toothless. The teeth in the upper and lower jaws are numerous and small, and whilst one set of teeth is being ground down, the several successional series are already functional. H. mirabilis has in all about 2000 teeth; the total length of the skeleton is 38 feet, of which nearly 4 feet are taken up by the skull; in other respects this genus is allied to Iguanodon.
Ornithomimus, of the Upper Cretaceous of Colorado, is known only from its fore- and hind-limbs. The fore-limbs are short, with three fingers. The hind-limbs are very long and strikingly bird-like. The metatarsals, of which only the second, third, and fourth are developed, are much elongated; the proximal half of the third is pushed back between the second and fourth, and imperfectly fused with them, exactly as in young birds. The astragalus has a long ascending process, and is fused with the tibia. The fibula is very slender, distally much reduced; the calcaneum is represented by a tiny nodule; the terminal phalanges end in pointed claws. O. grandis must have reached a considerable size, to judge from its middle metatarsal, which is 60 cm. or 2 feet long. Until more is known of these extraordinary creatures, nothing definite can be said about their affinities. They may perhaps belong to the Theropoda.
Order IV. CERATOPSIA.
Pubic bones simple, forming a symphysis, post-pubic branches being absent. The mandible carries a toothless "pre-dental," and the fused premaxillaries carry a similar, toothless, "rostral" bone.