928 HISTORICAL GEOLOGY. 



GENERAL OBSERVATIONS ON THE TERTIARY. 

 BIOLOGICAL CHANGES AND PROGRESS. 



The precursors of the Tertiary Mammals. — No immediate precursors of 

 the Tertiary non-marsupial or placental Mammals, linking them to the 

 Marsupial, have yet been found in any part of the world, notwithstanding 

 the occurrence in many regions over America as well as the other conti- 

 nents of a gradual passage from the Cretaceous formation into the Tertiary. 

 They are naturally supposed to have existed in the later Cretaceous over 

 the dry land of eastern and western America ; but still it is strange that 

 they did not find resorts somewhere on the border of the Cretaceous seas 

 along with the Marsupials. The nearest approach in the Eeptilian type to 

 the Mammalian yet known was made by the stupidest of the Dinosaurs, 

 which had a pair of Bovine horns and two-pronged teeth. 



Early prototy pic character. — Another strange fact is that although the 

 Marsupials of earlier time had become variously specialized, their placental 

 successors should have had unspecialized or prototype characteristics, such as 

 have been described ; that there should have been at this time so striking a 

 starting from what appears to be a new beginning. The removal of the 

 former mystery may also remove this. Moreover, it is to be considered that 

 among the fossils of the Mesozoic Marsupials, remains of the limbs, or of any 

 parts of the skeleton excepting the jaws and teeth, are of very rare occurrence. 



Diversity or Eocene Mammals. — Another remarkable fact is that so 

 great a diversity of Mammals, diversity in structure as well as size, should 

 have appeared before the Eocene period had passed. The prototypic plant- 

 eaters and flesh-eaters of the earliest part, supposed to be plantigrade in feet, 

 were followed, even in the Wasatch division of the Lower Eocene, by species 

 of large, short-footed Ungulates, the Coryphodonts, and in the later Eocene 

 huge Dinocerata, the latter supplied with horns for attack and defense. 

 In the Eocene, also, the Tapir-like species advanced far toward the modern 

 genera, Tapirus and Rhinoceros. There also appeared various species with 

 paired toes, in the line of the Hogs, Hippopotamus, Camel, so that the type 

 of Artiodactyls, and the types of several of its principal subdivisions, were 

 established. There were also some prominent Eocene types of Rodents and 

 Insectivores. Earther, the Quadrumana of the Early Eocene, having the 

 typical number of teeth, 44, were followed in the Later Eocene, by others, 

 in which the number of teeth was reduced to 32, the final limit in the 

 Quadrumana, and that characterizing Man. 



Moreover, there were several successions of Mammalian faunas in this 

 first period of the North American Tertiary, and the species in each of them 

 probably outnumbered those of Recent North America. The kinds found 

 fossil may have been a fourth of all then existing in the region, and 

 probably not more. 



Loss of prototype characters. — Very early in the Eocene, prototype charac- 



