ORDER vm DINOSAURIA 227 



known evidence of viviparous habits among Dinosaurs.^ During the last 

 quarter of the nineteenth century an abundance of well-preserved remains was 

 brought to light both in the Old World and in the New, which lent a fresh 

 impetus to their study. The division of the group into three sub-orders— 

 Theropoda, Sauropoda, and Predentata — was first proposed by 0. C. Marsh. 



Sub-Order 1. THEROPODA. Marsh.^ 



Carnivorous Dinosaurs with small cranium, the long axis of which is approximately 

 at right angles to that of the neck. Margin of the jaws provided with laterally com- 

 pressed thecodont cutting teeth. Brain-case incompletely ossified; antorbital vacuity 

 large. Mandibular ramus without coronoid process, and usually pierced by a lateral 

 foramen in its hinder half. Vertebral centra hollowed, the cervicals flattened in front, 

 and concave behind ; post-cervicals amphiplatyan or slightly amphicoelous. Sternum 

 unossified ; acetabidum perforate. Pubes slender, projecting simply downwards, and 

 united clistally, like the ischia, in a symphysis which is often much extended. Post- 

 pubic process not developed. Limb bones hollow, fore-limbs considerably shorter than the 

 hinder pair ; digits three to five in number, provided with prehensile claws ; hind feet 

 digitigrade. Femur with inner trochanter ; astragalus with ascending anterior process. 



The Theropoda were carnivorous land Dinosaurs provided with clawed 

 digits, and varying excessively in size. Compsognathus, the smallest known 

 Dinosaur, was no larger than a cat, and Megalosaurus attained the size of an 

 elephant. In outward appearance these animals must have been very 

 grotesque, owing to their habit of stalking about on their hind limbs, or possibly 

 even leaping in kangaroo-fashion (Hallopus), with the forward part of the body 

 lifted from the ground, and balanced by the powerfully developed tail. The 

 latter may have served in some cases also for a swimming organ, as well as a 

 support for the animal when resting on its hind quarters and pelvic symphyses. 

 The skeleton of many Theropoda was of very delicate construction, the vertebrae 

 being often, and the limb bones always, hollow. 



The skull is known in comparatively few genera. It is similar in the 

 main to that of the Sauropoda, but the brain-case is incompletely ossified, and 

 the sutures are often indistinct. The elongation of the cervical vertebrae is 

 an ornithic character, as pointed out by Cope. All the vertebrae of the neck, 

 except the a,tlas, are concave behind, but usually flattened on the anterior face 

 of the centra ; they are longer than the dorsals, and their neural spines are 

 only moderately developed, indicating a less powerful musculature than among 

 the Sauropoda. The cervical ribs are long and nearly straight, one of their 

 articular heads being attached to the centrum, and the other to the neural 

 arch. Each sacral rib is attached to two vertebrae ; the caudals are without 

 ribs, but chevron bones are strongly developed. Megalosaurus and Compsognoihus 

 are remarkable for the possession of abdominal ribs. 



1 Marsh, 0. C, Amer. Journ. Sci. [3], vol. XXI. (1881), p. 340. 



- Literature : 



Deslongchamps, E. E., Memoir sur le Poikilopleuron Bucklandii (Mem. Soc. Linn. Norm. vol. 

 VI. p. 36), 1838.— iVewiJo'/i, E. T., On Ornitliosuchus, etc. (Phil. Trans, vol. CLXXXV. B, p. 586), 

 1894. — Osborn, IT. F., Fore and hind limbs of Carnivorous Dinosaiirs from the Jurassic of Wyoming 

 'Bull. Amer. Mus. Nat. Hist. vol. XII. p. 161), 1898.— P/w^/yjs, J., Geology of Oxford and the 

 Valley of the Thames. Oxford, 1871. — -Plieninger, T., Ueber Zanclodon, etc. (Wiirtt. naturw. 

 Jahresh. vol. VIII. p. 389), 18.57. — Wagner, A., Ueber Compsognathus longipes, etc. (Abh. Bayer. 

 Akad. Wiss. II. Classe, vol. IX. p. 94), 1861. 



