The Deinodont Group

Matthew, W. D., & Brown, B., 1922, The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta., Bulletin of the American Museum of Natural History 56, pp. 365-385 : 374-375

4.— The Deinodont Group of the Cretaceous

Deinodon , including Gorgosaurus and Albertosaurus ; Dryptosaurus ; Tyrannosaurus , including Dynamosaurus

This group includes the large Upper Cretaceous dinosaurs. Gorgosaurus and Albertosaurus are very probably identical with Deinodon , and Dynamosaurus with Tyrannosaurus . Dryptosaurus is provisionally held distinct from Deinodon , which it much resembles. The essential features of this group are:

1.—Gigantic size and massive proportions.

2.—Skull relatively large with long deep jaw and large teeth. All fenestrse more or less reduced and arcades massive. Anterior teeth of U-shaped cross-section, (both crests posterior) the form changing progressively to the compressed oval section of the posterior teeth, with anterior and posterior serrate crest. Premaxillary teeth in the above genera much reduced in size.

3.—Quadrate closely united to quadratojugal, elongate, extending backward and downward.

4.—No fronto-parietal movement.

5.—Cervicals short and wide.

6.— Fore limb greatly reduced in relative size, moderately slender throughout.

7.—Manus peculiarly specialized, me. I very short and stout, me. II much longer, me. Ill vestigial, distal ends of metacarpals deeply grooved, phalanges rather short.

8.—Ungual phalanges of manus strongly curved and much compressed.

9.—Pelvic bones usually solidly united. Ilium elongate, extended far forward and decurved anteriorly with very short peduncle, ischium flattened distally and decurved, not expanded at the tip.

10.—Tibia and femur of subequal length, pes stout and massive and of moderate length.

11.—Lateral metatarsals massive, moderately long, median metatarsal broader than either at distal end, but the shaft greatly reduced, in the distal portion trigonal, the inferior sides closely appressed to the lateral metatarsal shafts, in the proximal portion reduced to a very slender rod between the lateral shafts; the head a little enlarged but enclosed dorsad and plantad by the large heads of the lateral metatarsals. The distal ends of the lateral mestarsals are convex both ways, that of the median plano-convex

12.—Phalanges of pes massive and rather short, the unguals moderately curved, uncompressed.

13.—Tail elongate, the distal caudals strongly interlocked by prolongation of the prezygapophyses.

The above analysis of characters shows that the deinodonts, although paralleling the megalosaurs in their huge size, massive proportions, short neck and large head, differ from them and resemble the coelurids and ornithomimids in the construction of the pelvis and the elongate quadrate. The pes has the very peculiar and specialized character of the Ornithomimidse very exactly reproduced, save for the greater massiveness of all its elements; the manus is nearer to that of the Cceluridae in some respects than to the megalosaurs, despite the diversity in the length of the phalanges, but might almost equally well be regarded as a specialization from that of Allosaurus . A review of the characters indicates that this group is not derived from the megalosaurs but from some primitive coelurosaurian with the specialized pes of the Ornithomimidae , but with the fore limb constructed more as in Coeluridae or in Allosaurus , although smaller and with the phalanges less elongate than in Coelurus . Such a type would probably be a slender, small, swiftfooted animal, for only in such a type can one understand the evolution of the remarkable specialization of the pes. The subject of the affinities and origin of the various groups of theropod dinosaurs will be ably and thoroughly discussed in an essay by Doctor von Huene to be published elsewhere, and the foregoing data, based upon comparison of the theropod skeletons on exhibition in the American Museum, are intended only to present the reasons for the taxonomic arrangement here adopted.

The point which we principally desire to make clear is that upon the above evidence the Deinodontidae must be regarded as a distinct and wellcharacterized family paralleling the megalosaurs but not derived from them, and that they cannot be included in that family as has been the general custom.