THE ERA OF THE FERNS 
appears, however, in the form of various conifers which 
are heralds of the domination exercised by the gymno- 
sperms in the following periods of the Mesozoic age. The 
great lepidodendrons and sigillarias of the Pennsylvanian 
period are disappearing and so are most of the seed 
ferns (pteridosperms). The giant equisetales become 
extinct and the sphenophyllum also disappears. Smaller 
types of lycopods and equisetales continue, and the seed 
ferns apparently have already given issue to a new type 
which spreads rapidly, the cycads. 
The desert-like landscape of the Karoo, with its not 
over-abundant vegetation, was populated with fair-sized 
reptiles of the great tribe which was to produce the 
giants of the Mesozoic age. They already show a 
tendency toward the grotesque appearance that is so 
pronounced in the next age. One of these Permian 
reptiles, called the dimetrodon, was about eight feet long 
and had spines about four feet long attached to its 
vertebrae and connected by a membrane which formed a 
fan-shaped screen on its back. Other reptiles of the 
period were lizards four feet long, like varanops, and 
giant salamanders. In the northern hemisphere, in 
Texas, where there was no glaciation and where we find 
a more opulent vegetation, though of the same type, 
great water reptiles also lived. 
77 
