CREATION BY EVOLUTION 



conform to the ideal conditions inferred to be the starting 

 point for later advances. 



The Mammal-Like Reptiles 



We come next to the theromorphs, mammal-like reptiles 

 of Permian and Triassic time, nearly all of which were 

 fierce carnivorous animals. The most primitive of these 

 were lizard-like forms from the Permian rocks of Texas 

 and Russia; but some of them, called pelycosaurs, were 

 specialized side lines. The most noteworthy advance by the 

 earlier members of this group was the development of an 

 opening, or temporal fossa, in the bony mask covering the 

 back part of the skull on each side behind the eyes. The 

 most primitive amphibians and reptiles had this temporal 

 region covered with a continuous shell of bone, but in the 

 mammal-like reptiles the tissue surrounding the jaw muscles 

 (which lay just beneath this bony shell) seems to have 

 acquired the power first of fastening itself to the surface 

 of the bone and then of sinking into the middle of the bony 

 area. Meanwhile the bone itself, while giving way in the 

 middle of the area, strengthened itself around the margins 

 of the area to which the jaw muscle was attached. In this 

 way bony arches grew up around the margins, and an open- 

 ing appeared toward the middle. Such openings have been 

 developed in different parts of the temporal region in dif- 

 ferent groups of reptiles; some reptiles had on each side 

 two temporal openings or fossae, one above the other, and 

 other reptiles had none. The mammal-like reptiles had 

 but one, which was surrounded in the later members of 

 the series by the postorbital, parietal, squamosal, and jugal 

 bones. This temporal fossa may be traced through the 

 ascending series of mammal-like reptiles into the early 

 mammals, thence into the tree-shrews, lemurs, monkeys, apes, 



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