374 Revieivs — E.. F. Oshorn — Extinct Rhinoceroses. 



II. — The Extinot Ehinoceroses. By Henkt Fairfield Osborn. 

 Mem. Amer. Mus. Nat. Hist., vol. i, pt. 3 (1898), pp. 75-164, 

 pis. xiia-xx. 



SINCE the appointment of Professor Osborn as Curator of Verte- 

 brate Paleeontology in 1892, the American Museum of Natural 

 History has published some of the most remarkable contributions to 

 our knowledge of the Tertiary Mammalia which have yet reached us 

 from the New World. Tear after year expeditions have been sent 

 to the West to make systematic geological explorations, and to 

 collect fossils in the Tertiary lake-deposits, which began to yield 

 their startling novelties to Leidy in the early fifties. The collections 

 have been prepared, and the best specimens mounted, under the 

 direction of a skilled preparator, Mr. Hermann. Preliminary 

 studies have then been made by Professor Osborn, Dr. Wortman, 

 Dr. W. D. Matthew, and Mr. Hatcher ; and the results have been 

 published in a series of " Bulletins," illustrated by the well-known 

 careful drawings of Mr. Rudolf Weber. 



A still more important departure has now been made, in the issue 

 of the first two sections of an exhaustive quarto memoir on the 

 extinct rhinoceroses by Professor Osborn himself. This is illustrated, 

 not onljr by diagrams and the usual text-figures of fossils, but also 

 by nine lithographed plates ; and the plan of the work is not 

 confined to a bare record of the facts, but also comprises a discussion 

 of some of the most fundamental problems in the philosophy of 

 Palaeontology. We commend the memoir both to the notice of the 

 specialist in the study of mammals, and to the general reader who 

 desires to become acquainted with the latest-discovered facts bearing 

 upon the phenomena of organic evolution. 



Professor Osborn first discusses the differentiation of the Hyraco- 

 donts, Amynodonts, and true Rhinoceroses. These, he remarks, 

 may be popularly described respectively as the Cursorial or Upland 

 Rhinoceroses, the Aquatic Rhinoceroses, and the True or Lowland 

 Ehinoceroses. To the first family belong agile, three-toed genera 

 (such as Hyracodon), simulating the Miocene horses in skeletal 

 structure and in the develojjment of true hoofs. To the second 

 family are referred short, heavy animals, with four-toed spreading 

 feet, enlarged canine teeth, and probably a prehensile lip or proboscis 

 (such as Metamynodon). The third family comprises rhinoceroses 

 much like those still surviving in the Old World, the extinct 

 American forms only differing from the latter in the non-develop- 

 ment of the nasal horn. These families were all differentiated, at 

 least in the North American area, before the middle portion of the 

 Eocene period ; and as they are traced upwards in time, they 

 exhibit a curiously parallel course in the evolution of the molar 

 teeth, while in the characters of the incisor teeth, skull, vertebra, 

 and limbs they rapidly become more and more divergent. Pro- 

 fessor Osborn describes this parallelism and divergence in detail and 

 adds much to the value of his memoir by giving concise tabular 

 summaries of his results. It is indeed strange that we should thus 



