45° 



HISTORICAL GEOLOGY 



They were at first marine animals, but late in the Paleozoic became 



adapted to brackish and possibly to fresh-water conditions, and 



there is evidence for the belief that some even 



lived in lagoons where the water was more 



salty than that of the sea. 



Scorpions (Fig. 423) first appear in the 

 Silurian, but probably lived in water and got 

 their oxygen there, not on land as do their 

 modern relatives, the ability to breathe in air 

 having been acquired later in the Paleozoic. 



Fishes 



Fragmentary fish remains have been found 

 in Silurian rocks (Fig. 424 A, B) of both 

 Europe and America. The fact that fishes 

 were abundant and of considerable variety in 

 the Devonian is presumptive evidence that a 

 somewhat varied fish fauna existed during 

 the closing days of the Silurian. 



Fig. 423. — Restoration of 

 a Silurian scorpion. 



Summary 





Life on the Land. — It is probable that the lands of the period were 

 clothed with plants, but if so, little evidence is afforded either from 



424 



Restorations of Silurian fishes (ostracoderms) : A> Thelodus; 

 B, Pteraspis. 



the remains of plants or of land animals. The highly developed land 

 plants of the Devonian (p. 467), however, are indirect evidence of the 



