THE PENNSYLVANIAN PERIOD 



385 



FIG. 405. A small brachi- 

 opod (Chonetes) common 

 in the later Paleozoic 

 rocks. 



the gymnosperms were represented in the Pennsylvanian 

 forests by Cordaites, a tree which com- 

 bined many of the characteristics of 

 the conifers and the palmlike cycads. 

 They had long sword-shaped leaves 

 and appear to belong to a distinctly 

 higher level of development than any 

 of the fernlike plants. 



Land animals diversified. In older 

 systems of rocks the remains of land 



animals have been found only rarely. In 

 the Pennsylvanian, however, with its well- 

 preserved plants, the finding of many air- 

 breathing animals 

 should be expected. 



Among the arthro- 

 pods, a variety of 

 insects (Fig. 408), 

 scorpions, centipedes, 

 and spiders testifies to the wide diver- 

 sification through which the group had 

 passed in the periods before. As yet, 

 however, the bees, butterflies, and other 

 highly specialized insects had not ap- 

 peared, a fact which gains added in- 



FIG. 406. A small 

 brachiopod (Pug- 

 nax) with sharply 

 folded shell. 



FIG. 407. A Pennsyl- 

 vanian scallop shell 

 ( Aviculopecten) . 



terest from the reflection that 

 the flowers on which these 

 animals now depend were like- 

 wise yet to come. 



Amphibians take the lead. 

 In the Mississippian period 

 amphibians are known to have 

 Far more abun- 

 of them are 



found in the coal-bearing rocks which followed. Nearly all 

 appear to have been like the salamanders in form, but many 



FIG. 408. A large winged insect been present, 

 from the Coal Measures of France. 



