FEATURES IN HISTORY OF LIFE ON PACIFIC COAST 

 terial is sufficiently complete to permit a tentative 

 reconstruction shown in Plate X. 



In the Upper Triassic limestones, reptilian re- 

 mains are also well represented, but are known only 

 from the exposures in northern California. Bones 

 have been found representing the ichthyosaurs and 

 another marine group, the thalattosaurs, peculiar 

 to California. While numerous fragments have been 

 obtained from these deposits, the skeletons are 

 nearly all imperfect and do not show the wonder- 

 ful preservation of the Middle Triassic specimens 

 from Nevada. 



The history of the ichthyosaurs represented in 

 the Middle and Upper Triassic of the western region 

 furnishes one of the most interesting studies of evo- 

 lution thus far known in the story of this group. 

 The Middle Triassic forms are much more primitive 

 in every respect than those of the Jurassic, and 

 show less advanced specialization of the limbs, tail, 

 eyes, and teeth for life on the high seas. The Upper 

 Triassic types are also relatively primitive, but are 

 intermediate between the Middle Triassic and the 

 Jurassic stages of evolution. 



It is worthy of note that of all the multitude of 

 kinds of marine reptiles known to have lived else- 

 where on the earth in the Jurassic and Cretaceous 

 periods, that is, in the second and third of the three 

 divisions of the great age of reptiles, only two or 

 three indeterminate fragments have been found in 

 the extensive exposures of rocks of these periods in 

 the Pacific Coast and Great Basin regions. One 

 specimen from the Cretaceous of California is doubt- 

 fully considered to represent a plesiosaur, a long- 

 necked reptile very abundant in the seas of the 

 world in Cretaceous time. 



BIRDS. Fossil remains of birds are among the 

 most uncommon of the relics preserved in the rocks, 

 and can be expected in relatively few localities. In 

 the western region remains of bird bones have been 

 found in several formations. Dr. L. H. Miller has 

 summarized all of our information on the distribu- 

 tion and history of this group in a paper in the Uni- 

 versity of California Publications in Geology. 



No birds are known from the western region 

 in beds older than the Oligocene, from which a 

 single bone has been obtained at Vancouver Island, 

 British Columbia. In the Miocene several frag- 

 ments are known from Nevada, from the Mohaye 

 Desert of California, and one from marine deposits 

 at Los Angeles. In the Pliocene the material is simi- 

 larly scanty and imperfect. 



The Pleistocene bird fauna of the West is excep- 



10 



