PLESIOSA UPS. 
103 
from the Cretaceous strata having a neck much exceeding the body and tail in 
length, and containing as many as forty vertebras. Marine and carnivorous in 
their habits, these formidable creatures probably lurked in shoal-water, from 
whence they darted their long necks to seize passing fishes in their jaws. 
In the groups mentioned the head was comparatively small, but in the huge 
pliosaurs ( Pliosaurus ) of the upper Oolitic strata the skull was of enormous 
size, attaining in some instances a length of 6 feet, and the neck proportionately 
short and thick. Their 
teeth had more or less 
triangular crowns, and 
in some cases, inclusive 
of the root, measured 
quite a foot in length. 
As is the case 
with all the higher 
aquatic V ertebrates, 
there is evidence to 
show that the plesio¬ 
saurs were originally 
derived from land 
animals; the repre¬ 
sentatives of the 
group found in the 
earlier (Triassic) 
Secondary rocks hav¬ 
ing limbs departing 
much less widely from 
the ordinary type, 
and bearing claws at the extremities of their digits. In the small lariosaur, which 
measured about a yard in length, the limbs appear to have been somewhat 
intermediate in structure between the clawless paddles of the true plesiosaurs 
and those of more ordinary reptiles; and the creatures were probably amphibious 
in their habits, spending part of their time on land, and part in the water. In the 
allied nothosaurs and simosaurs the limbs were better adapted for walking, from 
which we may infer that their owners were still more terrestrial in their habits. 
FRONT AND SIDE-VIEWS OF A NECK-VERTEBRA OF A PLESIOSAURI AN. 
pr.z , and pt.z, anterior and posterior articular surfaces of the arch ; co, rib. 
UPPER ASPECT OF THE SKELETON OF THE LARIOSAUR, A SMALL PLESIOSAURIAN. 
