The Coelurid 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 : 371-373

2.— The Coelurid Group of the Jurassic

Ornitholestes and Coelurus

Mr. Gilmore has given very strong reasons for regarding Ornitholestes as a synonym of Coelurus , and there can be no doubt that they are closely related. The characters of the coelurid group can, therefore, be defined from Ornitholestes , and its status and affinities estimated.

The redescription by Osborn 1 presents the principal characters: 1.—Small size and slender proportions.

2.—Skull relatively small, teeth small, compressed, the premaxillary teeth somewhat reduced and of U-shaped cross-section. Jaw short, not deep.

3.—Quadrate closely sutured to quadratojugal, elongated, and extending forward and downward (owing to reduced relative length of jaw).

4.—No fronto-parietal movement.

5.—Cervicals long and slender.

6.—Fore limb not greatly reduced, bones long and slender throughout.

7.—Manus peculiarly specialized, me. I very short and stout, divergent, me. II and III long, slender, parallel, III greatly reduced in diameter; distal ends of metacarpals heavily grooved. All phalanges very long and slim. The metacarpals have the same proportions as in Allosaurus but the phalanges are of wholly diverse type.

8.—Ungual phalanges of manus greatly compressed, strongly curved.

9.—Pelvic bones united. Ilium elongate, extended far forward and decurved anteriorly, without distinct peduncle. Ischia slender, long, flattened distally but not expanded.

10.—Tibia somewhat longer than femur, pes very long and slender, isotridactyl.

11.—Three long slim metatarsals, separate, somewhat appressed, median metatarsal not reduced proximally, vestigial 1st and 5th digits unknown, probably as in Megalosauridae .

12.—Ungual phalanges of pes of moderate length and curvature, not compressed.

13.—Tail elongate, not fully known but the distal caudals appear to be interlocked by prolongation anteriorly of the prezygapophyses;

The complete knowledge of the ornithomimid type shows that “ Ornitholestes ,” as is recognized by Osborn (1917, p. 733), can no longer be understood as ancestral to it. This is especially seen in the fore limb, which is quite as much specialized but in a different manner. Nor is there anything in the pes that especially suggests an ancestral stage of the peculiarly specialized ornithomimid pes, which, as Gilmore has shown, had already appeared in the Lower Cretaceous. It is none the less true that, except for the fore limb, we might regard Coelurus as not far from the ancestral type and that it may be considered as a collateral, although clearly not a direct ancestral, stage. But it would seem better to retain it in a separate family ( Cceluridae ) for the present.

As compared with Compsognathus , Coelurus is much more specialized. The Solenhofen skeleton shows, besides the three functional digits on the pes, a moderately reduced first and a vestige of the fifth; the manus has also three functional and two vestigial digits. The pubis is broad, the ischium very slender; many other details would no doubt show the far more primitive character of this little dinosaur. While it may be ancestral structurally to Coelurus , no especial evidence is apparent in Compsognathus of the specializations peculiar to the coelurid group and, again, being not far from contemporary it cannot be a direct ancestor.

Its relations to the megalosaurs are not very close, and it seems better to hold it as the type of a distinct family, Compsognathidae .