PRE-CAMBRIAN AND PALEOZOIC ERAS 

 Devonian Period 



155 



As intimated above, terrestrial plants were abundant in the Devonian 

 period. Some of these displayed the interesting transitional stages by which 

 water-dwelling plants were 

 able to make the change to life 

 in the air. Forests of seed ferns 

 existed at this time, some of 

 the individual plants reaching 

 a height of over 40 feet and 

 having a trunk diameter of 3 

 feet. 



Remains of terrestrial ani- 

 mals are relatively few. Several 

 species of spiders, a mite, and 

 the first air-breathing snails 

 are included in the group, as 

 are also the first terrestrial 

 vertebrates, the primitive am- 

 phibians known as labyrintho- 

 donts, to be discussed more 

 fully later. 



Invertebrate marine life 

 continued abundant. Brachio- 

 pods reached their zenith; cor- 

 als and crinoids occurred in 

 profusion. Trilobites, on the 

 other hand, continued to de- 

 cline. Doubtless they were the 

 prey of cephalopods and fishes. 

 In addition to nautiloids, 

 cephalopods were represented 

 by a group in which the suture 

 lines (p. 151) presented a 

 wavy or "loop-and-saddle" ap- 

 pearance (Fig. 8.13). These 



were the first ammonites, a group which underwent extensive development 

 in later periods. 



The Devonian is frequently called "the age of fishes." We have noted 

 that ostracoderms were found in the Silurian, and may have originated in 



FIG. 8.9. Ordovician nautiloid cephalopods. 

 (Reprinted by permission from Textbook of 

 Geology, Part II, Historical Geology, by Louis V. 

 Pirsson and Charles Schuchert, published by 

 John Wiley & Sons, Inc., 1915, p. 626.) 



