Now that we have adopted the biome system as 

 the point of departure for analysis of animal distribu- 

 tion, it is essential to learn something about the geo- 

 logical history of these community units : how they 

 were first formed, when they first became well de- 

 fined, how they dispersed over the world, and why 

 they came to occupy their present locations. When 

 we know the origin and geological history of vegeta- 

 tional communities on land, we will be better able to 

 understand the origin, differentiation, and present- 

 day distribution of the animal species that are com- 

 ponents of these communities (Epling 1944). A re- 

 view of geological succession generally will be helpful, 

 although we will be mostly concerned with trac- 

 ing the origin and historical development of the bi- 

 onics during the Tertiary Era alone (see Table 

 3-1). 



PHYSIOGRAPHIC CHANGES 



21 



Geographic 



Distribution of 



Communities: 



Paleo-ecology 



At the beginning of the Tertiary, some 

 60-70 million years ago, the interior of the North 

 American continent was still widely inundated by 

 the epicontinental seas of the Cretaceous period. As 

 these seas gradually receded, the continent acquired 

 its modern topographic appearance. The Mississippi 

 embayment area is an extension of the coastal^ plain 

 that continues around the Gulf of Mexico and north- 

 ward along the Atlantic coast. This coastal plain 

 emerged progressively throughout the Tertiary Era. 

 Its general character is much the same now as it has 

 always been — tidal salt marshes and estuaries inter- 

 mingled with shallow lagoons bounded by off-shore 

 bars. 



The Appalachian Mountain System first appeared 

 near the end of the Paleozoic era and had become 

 eroded to a peneplain by the beginning of the Ter- 

 tiary. A new uplift then occurred, and erosion again 

 followed. In the Miocene, only the Schooley pene- 

 plain, a nearly level surface only slightly above sea 

 level, remained. However, monadnocks, hills of re- 

 sistant rock rising some hundreds of meters, were left 

 projecting out of the Schooley peneplain. Mount 

 Monadnock, the White Mountains, Great Smokies, 

 Cumberland Mountains, among others, are such for- 

 mations. The Schooley peneplain subsequently un- 

 derwent a series of archings and uplifts until it 

 reached some 1200 m (4000 ft) above sea level 

 along the central axis to give the region its present- 

 day character. In New England, Pleistocene glacia- 

 tion covered these mountains, rounded them off, 

 scraped away the old soil, and left a poorer soil full 

 of boulders. 



The Ozark and Ouachita Mountains were also 

 formed at the close of the Palaeozoic, underwent sub- 



280 



