EVIDENCES— GEOLOGY 



131 



not abundant among fossils, but tho protective tubes and hard 

 teeth of marine AnneUda occur even as early as the Ordovician. 

 The Bryozoa, now rela- 

 tively imimportant, were 

 very numerous during the 

 upper Cretaceous. The 

 genera then living are now 

 extinct, however, while 

 those which followed dur- 

 ing the Pliocene are still 

 represented, in some cases 

 l)y the same species which 

 then existed. The Brach- 

 iopods show a very similar 

 course in their develop- 

 ment, but reached the 

 climax of diversity in the 

 Ordovician and Silurian, 

 and have since become 

 less numerous. Most of 

 the Tertiary species are 

 congeneric with those now 

 living. The Echinodermata 

 reached their climax in the 

 Paleozoic. They were 

 represented by three classes 

 which are now entirely 

 extinct. One, the Crinoidea 

 (Fig. 71), is represented 

 by a few living species 

 but was once well diver- 

 sified, and four, including 

 the sea cucumbers, sea 

 urchins, starfishes and 

 brittle stars have come 

 down from the early Pa- 

 leozoic. All of these 



are among the lower phyla of animals, and it is to be noted 

 that they extend well back toward the beginning of the fossil 

 record. 



Fig. 70. — Skeletons of typical Protozoa. 

 B, siliceous skeleton of a radiolarian, 

 Stauraspis stauracantha, x 170; C, 

 calcareoas skeleton of a typical fora- 

 minifer, Globigerina hidloidcs, x 30. 

 (From The Origin and Evolution of 

 Life bj' Henry Fairfield Osborn, 

 courtesy of Charles Scribner's Sons.) 



