Trachodon (Pteropelyx) selwyni, Lambe, 1902

Lambe L. M., 1902, New genera and species from the Belly River Series (mid-Cretaceous), Geological Survey of Canada Contributions to Canadian Palaeontology 3, pp. 25-81 : 69-70

Trachodon (Pteropelyx) selwyni . Sp. nov.

Plate III, figs. 2 and 3 .

This species is established principally on the evidence of teeth, of which a number from the lower jaw are shown on plate III . The teeth follow each other, quincuncially in the usual Trachodont manner, three or four occurring in the vertical series, but seven or eight can be counted obliquely. They replace each other from the inside and appear in the grinding surface in two or three functional rows. When three teeth belonging to the same vertical row are in use in the grinding surface at the same time (see fig. 3 of plate III ), the outer one is generally worn down to the root and the stump is ready to fall out, the middle one is about half Worn down, whilst the inner one is either just coming into use or is only slightly worn.

The teeth of this species differ from those of T. mirabilis, Leidy, in being rounded oval above, instead of terminating in a point. They are smooth in both species. A few minute, obliquely transverse strize are observed on the inargins of the teeth of T selwyni but they are practically smooth, the marginal, oi' border sculpture chariicíerislie of the teeth of the species described in the next following pages being absent A few, very large mandibular rami without teeth, one of which is represented in fig. 24, A, are supposed to belong to this species. A femur, provisionally associated with T selwyni, was secured during the summer of 1901. It measured about 1 ' 425 M. (56 inches) in length When perfect. It is.585 M. and.508 M. * in circum- feience above and blow the third trochanter respectively, and indicates 1 the size attained by some of the herbivorous dinosaurs during Mid-Cretaceous times. For the purpose of comparison a reduced figure OI-this ilnmense bone is given with a‘ similarly reduced drawing Of. the femur of Iguanodon mantelli, Uwen, from the Wealden of Filgate Forest, Sussex, England (/ see fig. 21 ).

.

.

Fig. 22 , illustrates,. in a diagrammatic manner, the general mode of succession of teeth in the genus Trachodon. The teeth are represented as they appear in transverse sections of the jaws, the heavy lines indicating the keeled enamelled crowns of the teeth. Thus although. in both _ the upper and lower jaws the teeth replace each other from the inner side, yet the enanielled surface ofthe CIOWH Of the teeth are on the inner side in the lower jaw but on the outer side in the maxilla.

With this species is connected the name of Dr. Alfred R. Ü. Selwyn, C. M. G., for many years, prior to 1894, Director of the Geological Survey.

Figures

PLATE III. Fig. 1. Trachodon (Pteropelyx) marginatus, Lambe, inner side of left ramus of lower jaw, showing the teeth; one-half the natural size. Page 73. e, coronoid process; a, symphyseal surface; b, inner wall of dental chamber; c, mandibular groove; d, foramen. Fig. 2. Trachodon (Pteropelyx) sclwyni, Lambe, inner surface of teeth of lower jaw, to show succession natural size. Page 69. Fig. 3. Grinding surface of teeth of same specimen; natural size. Fig. 4. Scapherpeton tectum, Cope, dorsal vertebra, from the left side; twice the natural size. Page 31. Fig. 5. View from the front, same specimen. Fig. 6. Scapherpeton tectum, atlas, front view; twice the natural size. Fig. 7. The same, viewed from behind. Fig. 8. The samc, side view from the lcft. y, diapophysis _; z, prezygapophysis; ê, postzygapophysís l; s, neural spine 5 x, anterior articural cup; w, neural canal; v, facet for occipital condyle of skull.

Fig.21.—A, front view of right femur of Trachodon selwyni, from Red Deer river B, front _ view of right femnr of Iguanodon 1mantelli, from the Wealden of England One-sixteenth naturalsize. h,head t,greattrochanter m, thirdtrochanter; c,innercondyle.

Fig. 22. -Diagrammatic representa- tioii of the growth of teeth in Traclzoclon. A, transverse section of t-he mandibular minus; B, transverse Swim' of the ınzıx« illa. The heavy lines represent the enzunelled surfaces of the erowns of the teeth. c, grinding surfaces d, much worn teeth c, partly worn teeth;f, sneeessional teeth in the same vertical row with d and e: g, for-amen: h, mandibular groove f, inner wall of dental chamber‘.