ANCIENT ANIMALS 



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derlike creatures; others were stout-bodied, with short tails and bellies 

 protected by bony plates upon which they rested except while walking. 

 Collectively they are sometimes called stegocephalians (meaning "roof- 

 headed") 1 on account of their boxlike skulls without openings except for 



sett) 



Fig. 27.18. Bones of the shoulder girdle and fin base in the lobe-finned fish Eusthenopteron 

 (left), and the corresponding bones in a primitive amphibian (right). The basic similarity 

 in limb pattern is evident. Some of the bones have been lost in the higher vertebrates. 

 cl, clavicle; cth, clei thrum; h, humerus; icl, interclavicle; r, radius; sc, scapula; scth, supra- 

 cleithrum; u, ulna. (Redrawn from Romer, The Vertebrate Body, by permission W. B. Saunders 

 Company.) 



Fig. 27.19. Changes in the skull, fish to reptile. The same bones can be recognized through- 

 out, but there is a steady decrease in the relative size of the posterior bones and enlargement 

 of the anterior part of the skull. The parietal bones (p) with the pineal opening between 

 them, and the postparietals (pp) have been shaded in the same way in all three skulls. 

 A, the lobe-finned fish, Osteolepis. B, the primitive labyrinthodont amphibian Ichthyostega 

 of the late Devonian or early Carboniferous. C, a cotylosaurian reptile, Romeria. (Redrawn 

 from Romer, by permission The Williams & Wilkins Company.) 



the eye orbits and nostrils. Most of them were carnivores like their an- 

 cestors the lobe fins. The most important of the stegocephalians were the 

 labyrinthodonts (Figs. 27.17, 19, and 20), which began in the Devonian as 

 small, chiefly aquatic types, became stouter limbed land dwellers in the 



1 This is not a taxonomic group, but a broad term including a variety of types, 

 many of which were not closely related to one another. 



