102 



NATURE 



[Dec. 4, 1879 



aberrant group, and the ample material now in the 

 museum, representing more than six hundred individuals, 

 will render their elucidation comparatively easy. 



With the toothed birds and the Pterodactyls, have been 

 found great numbers of Mosasauroids, a group of reptiles, 

 which, during Cretaceous times, attained an enormous 

 •development both as to numbers and the variety of forms 

 by which it was represented. Several new families, in- 

 cluding a number of new genera and many species, here 

 appeared, and flourished abundantly. The Tylosaitrida: 

 were very large, some of them being more than sixty feet 

 in length, whle the Edestosauride were much smaller. 

 The very abundant material secured, representing not 

 less than twelve hundred individuals belonging to this 

 order, has enabled Prof. Marsh to settle many doubtful 

 points with regard to the structure of these reptiles, and 

 to determine that they possessed hind paddles, and were 

 covered with dermal scutes. 



The Cretaceous formations of the West likewise have 

 yielded numerous turtles and other reptiles, and many 

 fishes, some of them of great interest, and very full series 

 of specimens of all of these, representing not less than 

 five thousand individuals, are at present in the Vale 

 College Museum. The fame of these discoveries has led 

 other explorers into the same field. A most formidable 

 rival in enthusiasm and energy is Prof. E. D. Cope, who 

 has filled the houses at Philadelphia with bones from the 

 West, who has published some valuable memoirs upon 

 them, and to whose work attention will be directed on 

 another occasion. 



Besides the discoveries made by Prof. Marsh and his 

 parties in the Cretaceous of the West, the old Eocene 

 lake-basins between the Rocky Mountains and the 

 Wahsatch Range were, during the summer of 1870, ex- 

 plored with most interesting results, their age being then 

 full)- determined and announced. Many remarkable 

 forms of life, most of them very different from anything 

 previously known, have been disinterred. Of all of these, 

 perhaps none are more extraordinary than the gigantic 

 Dittocerata, a new order recently established by Prof. 

 Marsh. These animals nearly equalled the elephant in 

 size, but with shorter limbs. The skull was furnished 

 with two or more pairs of horn cores, and with enormous 

 canine tusks similar to those of the walrus, while the 

 brain was proportionally smaller than in any other land 

 mammal. Three genera and several species are known. 

 These great creatures seem to have lived in considerable 

 numbers about the borders of the old Eocene lakes, and 

 their remains are found quite abundantly, buried in the 

 dirt that once formed the muddy bottom. Remains of 

 more than two hundred different individuals are now in 

 the Peabody Museum, and a volume descriptive of them 

 by their discoverer is now in course of preparation. 



Another new order of mammals, made known by the 

 same untiring anatomist from these same deposits, is that 

 of the Tillodontia. These animals are in many respects 

 very remarkable, and notably in presenting characters 

 which seem to indicate affinities with several widely dif- 

 ferent groups. Thus the skull, feet, and vertebra? re- 

 semble those of some carnivores ; the anterior incisors 

 forcibly remind one of the corresponding teeth in the 

 rodents ; the lower molars are of the Paleotherium ungu- 

 late type. Two families of this order are known : the 



Tillothcrida, in which only the incisors, and the Stylino- 

 donlidcc, in which all the teeth grow from persistent pulps. 

 The largest specimens of this order were about the size of 

 a tapir. 



From these Eocene deposits, too, were obtained the 

 first remains of fossil Qiiadritmana known from the New 

 World. These early primates, according to their dis- 

 coverer, seem to have relationships both with the 

 lemurs of the Old World, and with the South American 

 monkeys. Two families have been discovered : the 

 Lcmuravidce, named from the principal genus, Lemu- 

 ravits, which have forty-four teeth, and thsLimnotherida, 

 which have not more than forty. The large number of 

 genera and species by which this group is represented in 

 these Eocene deposits, show that, even at this early 

 period, the American primates had reached a high degree 

 of development, and enjoyed, up to that time at least, very 

 favourable conditions for their existence. They are all, 

 however, low generalised forms, the characters of their 

 teeth and other portions of the skeleton bearing consider- 

 able resemblance to the corresponding parts in the 

 ungulates and carnivores. Besides the groups already 

 mentioned, the same Eocene lake-basins yielded the 

 remains of marsupials and bats (neither of which had 

 before been found fossil in America), together with many 

 species of birds, serpents, lizards, and fishes. 



Since the original account of American fossil horses 

 given by Leidy, the Eocene strata of New Mexico and 

 Wyoming have yielded two very important ungulates, 

 which have helped to complete the history of the descent 

 of the horse, so well worked out by Prof. Marsh. These 

 relics carry back the ancestry of this familiar quadruped 

 to the oldest Tertiary time. The earliest form, Eohippus, 

 was about the size of a fox, had forty-four teeth, the 

 molars having short crowns, and being quite different in 

 form from the premolars. There were four well-deve- 

 loped toes, a rudiment of another on the forefoot, and 

 three toes behind. The structure of the feet and of the 

 teeth in Eohippus indicates, beyond question, that the 

 direct ancestral line to the modern horse had already 

 separated from the Perissodactyls. The second of these 

 ungulates, Orohippus, is from the Wyoming Eocene, and 

 is evidently next to Eohippus, which it now replaces in 

 the line of descent. In size it about equalled its prede- 

 cessor, but the rudimentary digit of the forefoot has 

 disappeared, and the last premolar has gone over to the 

 molar series. Another Eocene equine, discovered in 

 Utah, is Epihippus. 



The discoveries made by the Vale expeditions in the 

 " Miocene " and Pliocene formations of the Rocky Moun- 

 tains and the Pacific coast were scarcely less numerous and 

 interesting. From these deposits were obtained the large 

 series of specimens which served to complete the genea- 

 logical line of the horse from the four-footed Orohippus of 

 the Eocene to the large Equus fratemus of the later 

 Pliocene, which does not differ, appreciably, from the 

 horse of to-day. From the "Lower Miocene" comes Meso- 

 liippus, which is about the size of a sheep, and has three 

 usable toes of nearly equal size, and a long splint or 

 rudiment of another, corresponding to the second digit of 

 a five-toed foot. Miohippus, a somewhat later form, bears 

 a close resemblance to Mesohippus, but the side toes are 

 smaller, and the splint is very short. In Protohippus, 



