412 0. C. Marsh—American Jurassic Dinosaurs. 
SAUROPODA. 
A well marked group of gigantic Dinosaurs from the above 
horizon has been characterized by the writer as a distinct 
family, Atlantosauride, but they differ so widely from typical 
Dinosauria, that they belong rather in a suborder, which may 
be called Sauropoda, from the general character of the feet. 
They are the least specialized of the order, and in some charac- 
ters show such approach to the Mesozoic Crocodiles, as to sug- 
gest a common ancestry at no very remote period. 
The most marked characters of this group are as follows: 
1. The fore and hind limbs are nearly equal in size. 
2. The carpal and tarsal bones are distinct. 
3. The feet are plantigrade, with five toes on each foot. 
4. The precaudal vertebrz contain large cavities, apparently 
pneumatic. 
5. The neural arches are united to the centra by suture. 
6. The sacral vertebrze do not exceed four, and each supports 
its own transverse process. 
7. The chevrons have free articular extremities. 
nearly complete skeleton, and hence, in the present communl- 
cation, this genus will be mainly used to illustrate the group. 
Morosaurus, Marsh, 1878. : 
The head in this genus was very small. The skull shows in 
its fixed quadrates and some other features a resemblance to 
eral form is shown in Plate V, figures 1 and 2. The neck was 
elongated, and, except the atlas, all the cervical vertebre have 
eep cavities in the sides of the centra, similar to those in birds 
of flight. (Plate V, figures 3 and 5). They are also strongly 
opisthoccelous. The atlas and axis are not ankylosed together, 
and the elements of the atlas are distinct. The supero-lateral 
pieces unite with the axis by zygapophyses, (Plate V, figure 4, Z). 
* This Journal, xiv, pp. 87, 514; xv, pp. 241. 
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