1876. ] Geology and Paleontology. 437 
rudimentary wings, and the vertebre as in modern birds. The type 
genus is Hesperornis, and three species are known. The second order 
embraces at present only small birds with powerful wings, and biconcave 
vertebre. The type genus is Ichthyornis, and the geological horizon is 
upper Cretaceous. Another discovery of importance from the same for- 
mation was pterodactyls, or flying reptiles, the first detected in this coun- 
7- These are of much interest, on account of their enormous size, — 
some having a spread of wings of more than twenty-five feet, — but es- 
pecially as they were destitute of teeth, and hence resemble recent birds. 
They form a new order Pteranodontia, from the typical genus Pteranodon, 
six species of which are now known. With these fossils were found 
_ large numbers of Mosasauroid reptiles, and remains of more than five 
hundred different individuals were collected. These proved to belong to 
two new families, Tylosauridæ and Edestosauride. Some of the former 
attained a length of sixty feet, while the latter were much shorter, the 
smallest being less than ten feet. These groups included several new 
genera and many species. This large series of specimens enabled Pro- 
fessor Marsh to clear up many doubtful points in the structure of*these 
: reptiles, and to determine that they possessed hind paddles, and were 
covered, in part at least, with bony dermal scutes. Many other birds, 
reptiles, and fishes were found in the same Cretaceous strata. 
The discoveries of Professor Marsh and party in the Tertiary of the 
West were of no less importance. The most interesting are those made 
in the two Eocene lake-basins between the Rocky Mountains and the 
; Wahsatch Range. These basins were explored by Professor Marsh in 
1870, and their Eocene age then first determined. His explorations in 
this region have secured to science over one hundred and fifty species of 
: new vertebrates, most of them widely different from any hitherto known. 
The most remarkable of these are the gigantic mammals of the new order 
Dinocerata, the type genus of which is Dinoceras. These animals nearly 
: equaled the elephant in size, but the limbs were shorter. The skull 
: was armed with two or more pairs of horn-cores, and with enormous 
: canine tusks, similar to those of the walrus. The brain was propor- 
tionally smaller than in any other land mammal. Three genera and 
Several species are known. Remains of more than one hundred dis- 
tinct individuals were obtained, and are now in the Yale Museum. The 
Tillodontia are another new order of mammals discovered in the same 
3 Eocene deposits. They possess many remarkable characters, which indi- 
Cate affinities with the Carnivores, Rodents, and Ungulates. There are 
two well-marked families, the Tillotheride, from the typical genus Tillo- 
: é um, which has rodent-like incisors; and the Stylinodontide, in 
- Which all the teeth grew from persistent pulps. The largest of these 
. Peculiar animals was about the size of a tapir. One of the most inter- 
esting discoveries made by Professor Marsh in the Eocene of Wyoming 
Was the remains of Quadrumana, the first found in the strata of America. 
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