Ornithomimus velox, Marsh, 1890

Marsh, O. C., 1890, Description of new dinosaurian reptiles, American Journal of Science 39 (229), pp. 81-87 : 84-85

Ornithomimus velox , gen. et sp. nov.

The high degree of specialization in the reptiles above described has a partial parallel in a small group of typical Ornithopoda from the same horizon. Various specimens of these, recently secured, represent a distinct genus and several species. The most marked characters already determined are manifest in the limbs and feet, and these have been selected for description in the present notice. A typical example is shown on Plate I, figures 1-3 , which is the type specimen of the species here described.

On the distal part of the tibia represented in figure 1 , the astragalus is seen in place, with a very large ascending process, larger than in any dinosaur hitherto known. The calcaneum is also shown in position, but the slender fibula is absent. This bone was complete, but of little functional value. The tibia and all the larger limb bones were hollow, with thin walls, as indicated in the section, figure 1, c .

In figure 5 , the corresponding parts of a young ostrich are shown for comparison. The slender, incomplete fibula is in place beside the tibia. The astragalus with its ascending process, and the distinct calcaneum, are also shown in position. The almost exact correspondence of these different parts in the bird and reptile will be manifest to every anatomist.

The most striking feature of the foot belonging with the reptilian tibia is shown in the metatarsals represented in figure 2, A . These are three in number, and are in the same position as in life. They are the three functional metatarsals of the typical Ornithopoda and of Birds. The distal ends of these bones correspond in size and relative position in the two groups, but here, in the present specimen, the reptilian features cease, and those of typical Birds replace them. In all the reptiles known hitherto, and especially in Dinosaurs, the second, third, and fourth metatarsals are prominent in front, at their proximal ends, and the third is usually the largest and strongest. In birds, the place of the third is taken above by the second and fourth, the third being crowded backward, and very much diminished in size.

This character is well shown in figure 6 , which represents the second, third, and fourth metatarsals of a young turkey, with the tarsal bones absent. In the reptilian metatarsals seen in figure 2 , the same arrangement is shown, with the tarsals in place. The second and fourth metatarsals have increased much in size in the upper portion, and meet each other in front.

The third metatarsal, usually the largest and the most robust throughout, here diminishes in size upward, and takes a subordinate, posterior position, as in birds. The correspondence between the metatarsals of the bird and reptile are here as strongly marked as in the tibiae and their accompanying elements, above described.

In figure 3 , the three phalanges represented belong with the second metatarsal, ard were found together in place.

The three metacarpals represented in figure 4 were found together in position, near the remains of the hind limb here described. Their very small size indicates that they may possibly belong to a smaller individual, but, with this exception, there is no reason why they do not pertain to the same specimen as the hind foot.

The remains of the present species here described were found in the Ceratops beds of Colorado.

Figures

Explanation of Plate I. Figure 1.—Left tibia of Ornithomimus velox, Marsh; A, front view; b, distal end; c, transverse section. Figure 2.—Left metatarsals of same specimen; A, front view; b, proximal ends; c, transverse section; d, distal ends. Figure 3.—Phalanges of second digit of same foot; front view, a, first phalange; b, second phalange; c, third, or terminal phalange. Figure 4.—Left metacarpals of same species, perhaps of smaller individual; front view. Figure 5.—Left tibia of young Ostrich (Struthio camelus, Linn.); a, front view; b, distal end. The separate calcaneum was first observed by the writer’s assistant, Dr. G-. Baur, who prepared the specimen. Figure 6.—Left metatarsals of young turkey (Meleagris gallipavo, Linn.); a, front view; b, proximal ends. a, astragalus; as, ascending process of astragalus; c, calcaneum; f, fibula; f' face for fibula; II, second metatarsal; III, third metatarsal; iv, fourth metatarsal. Figures 1-4 are one-third natural size, and figures 5 and 6, one-half natural size.