266 
PALEONTOLOGY: H, F. OSBORN 
mastodon and of Mceritherium, which were at once regarded as the solution of 
the ancestry of the Proboscideans. These animals took their place in all 
literature as two steps in the early evolution of this remarkable group. 
In 1909^ Osborn pointed out that Mxritherium is to be regarded as a ter- 
restrial form of the Sirenians (manatees and dugongs) in no way directly re- 
lated to the Proboscideans. It now appears that Palceomastodon must also 
be removed from its generalized position and be regarded as the ancestor of 
the long-jawed mastodons only; it is far too much specialized in the longi- 
rostral direction to be ancestral to the Proboscidea in general. These long- 
jawed mastodons are distinguished by the peculiar use of the front teeth of 
the lower jaw, which together made a broadly flattened, spoon-shaped tooth, 
FIG. 1 
Outiine of the mounted skeleton of Megabelodon in The American Museum of Natural 
History, discovered by E. L. Troxell in the Middle Pliocene of Texas. Drawing one forty- 
fifth natural size. 
almost entirely enamel covered. Phases of the evolution of this long-jawed 
phylum are seen in the classic Trilophodon angustidens of Cuvier, in the lower 
Miocene of France. A branch reached Texas in the Upper Miocene (Trilo- 
phodon productus of Cope), and Florida as well as Texas in the Trilophodon 
serridens of Cope. It attained gigantic proportions in the Middle Pliocene. 
The Megabelodon of Barbour, a superb skeleton of a long-jawed and extremely 
short-limbed Proboscidean, recently discovered in Texas by Mr. E. L. Troxell, 
has been mounted in The American Museum of Natural History. It repre- 
sents one of the culminating stages in the evolution of the long- jawed mas- 
todons. In these animals we find proof of nearly direct linear descent from 
the Palosomastodon of the Fayum, e.g., the long enamel band on the upper 
tusks, the broadly spoon-shaped arrangement of the lower tusks with enamel 
covering. In massiveness these animals parallel and even surpass the true 
mastodons of the Pleistocene, to which they are only indirectly related. 
^Osborn, 1900, 182. 2 0sborn, 1909, 332. 
