Ornithomimus altus Lambe 1902

Ornithomimus altus. Sp. nov.

Plates XIII and XIV, and plate XV, figs. 1 -8.

A hitherto undescribed species of dinosaur, belonging to the Omilhumimidœ and referable to the genus Ornithomimus of Marsh, is represented by a complete right hind limb (including the foot), the phalanges of the left foot in place, a pubic bone, and an ischium, of individual.

\Vith these, as probably belonging to the same species, are included a posterior dorsal vertebra, caudal vertebrae of remarkable form, phalanges of the manus and a number of teeth of peculiar shape.

The femur, tibia, metatarsals and phalanges of the pes, except the terminal ones. are hollow.

The femur is shorter than the tibia. The astragalus is closely applied to but does not coalesce with the distal end of the tibia; it has a well developed ascending process apposed to the front face of the tibia. The fibula is slender and the tibia has a prominent cnemial crest. The calcaneum and the tarsal bones were found in place. Metatarsal III, as in Ornithomimus velox * Marsh, fits closely against metatarsals II and IV, and is, a short distance above its distal end, triangular in section with its flat face foremost. It becomes attenuated above and passes behind the other two metatarsals. Metatarsal V, represented by a short, laterally compressed, slightly curved boııe, lies close to the proximal end of metatarsal IV.

The phalangeal formula is 3, 4, 5; digit III is the longest and digits II and IV are of about equal length. The terminal phalanges are sharply pointed in front, rather straight, flattened below and deeply grooved on the sides. The grooves are carried forward to the extreme point and indicate the presence, during life, of a long but not sharply curved or pointed claw. The other phalanges have deep pits, one on each side of their distal extremities. The shape of the terminal phalanges suggests afoot, not suitable for grasping but adapted rather for speed in running, an idea carried out by the slenderness and lightness of all the bones of the leg.

The posterior dorsal vertebra, plate XIV, fig. 1, is decidedly amphicœlous, the concavity in the anterior face of the centrum being more marked than in the posterior one. The centrum is constricted at mid-length só as to have concave sides and lower surface, there being at either end of the latter a broad median groove. The neural arch does not reach far below the top of the centrum. The diapophyses (imperfect in the specimen) have stout bases, relatively broad in their antero-posterior diameters. The faces of the prezygapophyses are directed obliquely inward. The neural spine is well developed, short, deep from back to front, shallowly concave on its sides, with rugose, slightly excavated, anterior and posterior surfaces. The centrum is hollow, its walls dense and about 2 ' 5 mm. thick at mid-length, the inner space extending to within about 6 mm. of either end.

’Sixteenth Annual Report, U. S. Geol. 1896 Iviii Survey,, plate., fig. 2.

The caudal vertebrae, plate XIV., figs. 2-—5, and plate XV., figs. 1—5, supposed to belong to this species, are remarkable for the suppression of the neural spine and the forward horizontal extension of the prezygapophyses to a distance in advance of the anterior end of the centrum nearly equal to the length of the centrum itself. The postzygapophyses are represented by a backwal‘dly directed, laterally compressed, nearly horizontal process that fitted between the prolonged prezygapophysial processes of the succeeding vertebra. The centrum is long‘ compared with its height, slightly concave on its sides and lower surface, with a strong median groove below. In different specimens its interior may be moderately hollow or instead a number of Vacuities of variable size may be present. Small facets, for the attachment of the chevron bones, are present at the lower, posterior ends of the centra; these are not recognized at the anterior ends. The neural spine is sometimes represented by a narrow, rounded ridge (shown at “ w ” in the specimen figured on plate XV., fig. 2). The prezygapophysiatl processes are broadly expanded laterally, contracting and thinning gradually anteriorly, their outer edges overhanging the sides of the anterior end of the centrum and extending lower than the median upper surface of the same; their lower surfaces are slightly striated longitutlinally. The neural canal is small, its outlet, anteriorly, is wider than high and is roofed over to a point above the anterior end of_ the centrum. These caudal vertebrae indicate a tail of considerable length but their manner of articulation would scarcely admit of much lateral motion.

A number of phalanges of the supposed manus of this species are also hollow but present a difference in the shape of the terminal phalangcs which are curved and laterally compressed with a groove on e-ach side extending‘ from the apex backward and dividing into two branches toward the proximal end. Judging from the size of these phalanges the manus was smaller than the pes, and their shape suggests a grasping capacity; the terminal phalanges were probably encased in sharp, hooked claws giving their possessor the power of tearing its prey.

Two bones, probably the distal ends of the first metatarsalif and the first metacarpal, were found with, the phalanges of the manus above referred to, phalanges of the pes, a separate astragalus and a ealc-aneum.

" “ Fore and Hind Limbs of Carnivorous and Herbivorous Dinosaurs from the Jurassic of \\'yo ning, ” Bulletin Am. | Mus. Nat. Hist., vol..\ 'ii., 1899, by Henry Fairfield Osborn, tigs. 3, ~1- und 4a.

[table omitted]

The tooth represented in figs. 12 and 13 ofplate XIV is provisionally associated With this species and is regarded as being from the anterior portion of the jaw. A similar tooth, figured by Leidy, in his memoir on the Judith river vertebrata (Trans. Amer. Philos. Soc. 1859) is referred to in his description of the teeth of Deinodon horridus as an aber- rantly formed specimen. Leidy suspected the tooth to be an incisor.

In the tooth figured on plate XIV, one only of the posterior keels is denticulated and that only for a short distance at the centre of its length; the other is smooth. Another specimen is apparently Without denticulations.

A number of teeth of this shape, With others intermediate iii form between them and the orthodox Megalosauroid tooth, Were collected in the Red Deer river district. They are referred to the present species on account of their frequent occurrence With and near the remalns of O. altus.

The estimated length of Ornithomimus altus is 22 feet.

Belly River series, Red Deer river, 1897, 1898 and 1901. The right hind limb with the phalanges of the left foot, Were found in 1901, below Berry creek.

The following remains of this species besides those already mentioned have been collected by Professor.Iohn Maeonn, in 1880, on Mackay creek, near Walsh on the line of the (LER, phalanx of pes (Belly River series); by Mr. T. C. Weston, in 1884, at Ross coulée, near Irvine, about eighteen miles east of Medicine Hat, part of a caudal vertebra, phalanges of the pes and a phalanx of the manus (Belly River series); by Dir. Weston, in 1889, part of a caudal vertebra and phalanges of pes, labelled, Red Deer river, range xxi, tp. 32 West of 4th RM. (Edmonton series).