440 MISSISSIPPIAN PERIOD 



apparently, than in any later period. Some 600 species are known, 

 more than half of them from North America. The fossils are chiefly 

 teeth, spines, and dermal ossicles. Three-fourths of the species had 

 crushing or pavement teeth, adapted to breaking the shells of 

 mollusks and crustaceans, and the trituration of seaweeds. The 

 arthrodirans and lung fishes had declined, as compared with the 

 Devonian period. Of fishes frequenting inland and coastal waters, 

 probably the culminating type was of the order to which the modern 

 garpike belongs. The curious tribe of ostracoderms (p. 686) had 

 nearly or quite disappeared. 



Land Life 



The record of land life is poor, but enough fossil plants have 

 been found to show that the plant life of the early Mississippian 

 land was little more than an expansion of that of the preceding 

 period. There were, however, notable changes in detail. The geo- 

 graphic diversity of the Mississippian floras was somewhat greater 

 than that of the Devonian. The mid-Mississippian flora is 

 thought by White * to have had its origin on the islands of western 

 Europe, and to have spread thence to Siberia and southward, even 

 to South Africa and Australia; but by what route is not known. 

 Seventy-five per cent of the species of a Mississippian flora of Argen- 

 tina are identical with European species, a fact which suggests 

 strongly a land bridge between South America and the continents 

 just named. 



The flora of the closing stages of the period indicates adverse 

 conditions of life, and prepares the way for the great floral changes 

 which followed. From this stage comes the earliest wood which 

 shows rings. 



The most interesting suggestion of advance in land life is found 

 in the footprints of a supposed amphibian from the Mauch Chunk 

 shale of Pennsylvania. They imply a stride of about thirteen 

 inches, and a breadth between outer toes of eight inches. Nearly 

 complete specimens of amphibia (labyrinthodonts) have been found 

 in the Lower Carboniferous of Scotland. 



Probably insects and their allies lived, but their fossils have not 

 been found. 



1 Jour, of Geol., Vol. XVII, 1909. 



