24 FIELD MUSEUM OF NATURAL HISTORY 
tana by a special Museum expedition in 1904. Parts of the skele- 
ton of the same individual will be found in a wall case adjoining. 
Hadrosaurus, illustrated by a restoration, is a large biped rep- 
tile found in the Cretaceous deposits of New Jersey. The ani- 
mal walked entirely upon its hind legs, only using the smaller 
forward pair when resting or feeding. 
Mosasaurs were a new type of marine reptile which appeared 
with the Cretaceous period. They were short-necked, round- 
bodied, long-tailed animals, with pointed snouts. The skeletons 
of these animals are found in large numbers in the chalk beds 
of western Kansas ; also in England and Belgium. They are rep- 
resented in the collection chiefly by a complete skeleton of Platy- 
carpus from Kansas. (Hall 59.) 
Plesiosaurs were a second type of marine reptile which, as 
has been mentioned, appeared in the Jurassic period and con- 
tinued to the close of the Cretaceous. The specimen of Elas~ 
mosaurus shows the shoulder and pelvic girdles in connection 
with a complete paddle. (Hall 59.) 
Pterodactyls, or flying reptiles, represent one of the strangest 
forms assumed by reptilian life toward the close of the Mesozoic 
era. They were very slight and active creatures, somewhat bat- 
like in general appearance, but withal distinctly reptilian. The 
head was armed with a stout, bird-like beak, the bones were 
hollow and the wing-bones were long and supported a mem- 
brane which connected with the legs, thus forming the organ of 
flight. In powers of flight they doubtless equaled any of the ex- 
isting birds. The group is represented by a splendid skeleton 
of Nyctosaurus from the chalk beds of Kansas. This is the most 
complete specimen known. (Hall 59.) 
Tertiary Period^ or Age of Mammals. — Tertiary plants and in- 
vertebrate fossils shown include leaves of Flabellariaj a palm 
which grew in the Eocene epoch near Green River, Wyoming. 
Also, leaves of Acer^ or maple, and other trees of modern 
genera are shown. 
Such remains, with others that are found, indicate that a 
subtropical climate, like that of Florida, prevailed at this period 
over the northern United States. Even so far north as Green- 
land, the climate was so mild that cypress and cedar trees grew 
in profusion. 
