RELATIONS AMONG SPECIES 



377 



times. Perhaps most spectacular in the general trend 

 of Cenozoic persistence of modern types of reptiles 

 were strange distribution patterns that included far 

 norther localities when the areas possessed warm 

 climates. In addition, the Eocene featured a snake 

 related to our boa constrictor that was 35 feet long, 

 and the Pleistocene featured land turtles slightly 

 larger than the present giants on the Galapagos 

 Islands. 



Cenozoic bird evolution has not been dramatic 

 since the Eocene appearance of most modern bird 

 orders. Somewhat remarkable in view of modern 

 times was the Eocene start of large, flightless birds. 

 The Eocene featured a form almost seven feet tall and 

 the Miocene a form almost eight feet tall. However, 

 the tallest bird was alive up to a few centuries ago in 

 New Zealand. This ostrichlike bird was about ten 

 feet tall. It was destroyed by man, the Maoris. 



Po/eocene and Eocene. The start of the Tertiary 

 was a time of great geological change. The continents 

 rose and mountains formed. North America assumed 

 much of its present outline (Figure 19.13). The Ap- 

 palachians were being degraded. The area from the 

 Appalachians to the Rockies rose above sea level and 

 probably was mostly a site subject to erosion and 

 some uplift in the west. In the Rockies folding and 

 faulting continued locally into the Eocene. In most 

 places in California now having mountains the forces 

 of mountain building, especially vulcanism, were ac- 

 tive. Western areas of Washington and Oregon ob- 

 tained vast flows of basalt, and parts of Wyoming had 

 like flows of andesite. Also, the various basins in 

 Wyoming, western Colorado, eastern Utah, north- 

 western New Mexico, and perhaps northeastern Ari- 

 zona seem to have contained many very large lakes. 

 However, these lakes probably were ineffective as 

 major barriers and major molders of the evolution of 

 further life. 



In spite of these geological events, there appears 

 to have been little latitudinal modification of previous 

 climatic or geoflora conditions. Although latitudinal 

 zonation remained much the same, the elevation of 

 ancient Coast Ranges and Sierras produced a rain 

 shadow, hence a drier climate in the region of the 

 present southwestern deserts. This rain-shadow site 

 became the place of Madro-Tertiary Geoflora origin 

 and later development (Figure 19.14). 



The geoflora elements of this time indicate that 

 there were both horizontal and vertical variations in 

 climate. Also, the Arcto-Tertiary of this early Terti- 



Flgure 19.13 Paleocene to Early Eocene paleogeogrophy, including 

 the distribution of geofloros and major mountains. Symbols as in Figure 

 19.12, plus marsh along western Gulf Coast. Black areas indicate inland 

 lakes. 



ary had most of the present-day elements, but not 

 with their present distribution. For example, the cen- 

 tral part of our continent had dawn redwood, ginkgo, 

 sycamore, alder, oak, chestnut, hazlenut, and poplar 

 or Cottonwood. 



The types of Paleocene and early Eocene mammals 

 indicate that definite connection existed between 

 North and South America. In the late Eocene this 

 Panamanian land bridge was closed and seems to 

 have remained closed, except as a sweepstake route, 

 until the Pliocene. Also, early Eocene to Pliocene 

 fauna indicate the necessity of movements between 

 North America and Asia via a Bering land bridge. 

 However, the Bering land bridge closed in middle 

 Eocene, reopened in late Eocene, and stayed open, 

 except for brief and minor disconnections, until the 

 cycle of recurrent opening and closing during the 

 Pleistocene. 



The Paleocene was the dawn of most to all of the 



