152 CHAPTERS ON EVOLUTION'. 



the most, any one record of what has been done towards supplying 

 " missing links " must be held to be merely provisional, and to serve 

 but as a prelude to the discoveries of a succeeding period. Espe- 

 cially within the last few years, however, has the evidence of the 

 existence of animals which may fairly be deemed " missing links " 

 accumulated in a very marked degree, and in some cases in a very 

 astonishing fashion. The reader has but to become informed of 

 recent discoveries amidst the Tertiary rocks of North America, to 

 learn the surprising revelations concerning intermediate forms between 

 existing groups of mammals or quadrupeds, which, chiefly through the 

 researches of Professor Marsh, have been aolded to the conquests of 

 science. What, for example, is to be said of the zoological position 

 of the huge Dinoceras (Fig. 71) and its allies, creatures as large as 

 existing elephants, and which, from the examination of their skeletal 

 remains, can at the best be regarded as intermediate betwixt the 

 elephants themselves, and the odd- toed Ungulates (or hoofed quad- 

 rupeds), such as the rhino- 

 ceroses, &c. ? Dinoceras thus 

 possessed two large canine 

 teeth (cc), six small molars (m) 

 on each side, and four horn- 

 cores (h l h 2 ), besides a pair of 

 similar structures in front of 

 the upper jaw. Or, again, 

 which rank, save that of an 

 intermediate position, and as 

 a veritable group of "missing 

 links," can be assigned to the 

 FIG. 71. SKULL OF DINOCERAS. extinct quadrupeds, included 



by Marsh under the collective 



name Tillodontia, the remains of which occur in the Eocene Tertiaries 

 of the United States ? For how else should we classify animals with 

 great front teeth like the Rodents or "gnawers," grinders like the 

 Ungulates or hoofed quadrupeds, and a skull and skeleton generally 

 like that of the carnivorous Bears ? Or, once more, what can be 

 said of the affinities or relationship of the extinct Toxodonts, also 

 from American deposits, in which the characters of Rodents are 

 united to those of Ungulates and Edentates the latter being a 

 group of animals represented by the existing sloths, armadillos, and 

 ant-eaters ? Nor is the list of extinct quadrupeds which fall into 

 no existing group, but present a union of the characters of several 

 distinct divisions, exhausted with the foregoing brief chronicle. 

 Again drawing upon the well-nigh inexhaustible treasure-house of 

 geological specimens in the recent deposits of the New World, we find 

 the extinct Marauchenia connecting the odd-toed hoofed mammals 



