no THE PERMO-CARBONIFEROUS RED BEDS OF 



predatory forms have fixed upon certain harmless forms as their most desir- 

 able victims, and the harmless forms must seek safety in flight, concealment, 

 or a defensive armor. Between the forms which seek to protect themselves 

 by an armor and the predatory forms an active competition generally develops, 

 the armor growing heavier and more complex, and the weapons of the attack- 

 ing forms becoming stronger and more efficient. More than once in the 

 history of the earth such a competition has continued to the complete extinc- 

 tion of both sides, because the armor became an impossible burden, and the 

 weapons of attack became so specialized that the food-supply was greatly 

 restricted. 



In the Permo-Carbonifcrous vertebrate fauna of North America this con- 

 test had reached only into its early stages. Certain amphibians, and at least 

 one reptile, had developed more or less perfect protecting-plates on the back 

 and sides. In DissorJiopIius, Cacops, and Alegciiiosaunis the distal ends of the 

 neural spines are more or less expanded into overarching plates, and a set of 

 secondary plates lies above and alternates with the expansions of the neural 

 spines. In Aspidosaurns the protection was confined to the expansion of the 

 neural spines. In BroUicUiis there are dorsal shields not attached to the 

 neural spines which are not expanded distally. Dissorophiis was perhaps the 

 best protected of this group, for the plates descended far down over the sides 

 in a manner which led Cope to refer to it as a "batrachian armadillo." In 

 the other genera mentioned the protecting plates are confined to the midline 

 of the back, and in Cacops to the anterior portion only. 



The armor of Diadecles, so far as known, is confined to three plates which 

 overlie the sixth, seventh, and eighth ribs beneath the scapula. The charac- 

 ter of the distal ends of the neural spines and the outer surface of the ilium 

 has led to repeated suggestions that there was a series of median dorsal 

 dermal elements, as in Pareiasaurus, and perhaps a plate, or plates, over the 

 pelvic region, but there has been no confirmation of these ideas. 



Newman "* has recently drawn attention to the fact that in the Texas 

 armadillo the armor is not efficient in repelling the attack of dogs used in 

 hunting it, for the dogs frequently bite through the bony dorsal plates. He 

 suggests that the armor may be of greater use to the animal as a protection 

 against the thick brush or thorns or even the jagged sides of narrow crevices 

 in the rocks into which the animal crowds for safety when it is pursued. The 

 fact that the armor is much worn in old age is cited in support of this view. 

 If this idea is correct, it would afford some support to the suggestion of the 

 author that the Dissorhophidcr and Aspidosauridcc were largely terrestrial in 

 habit. 



Aside from the abdominal ribs which occur in many of the smaller forms, 

 and which can not be reckoned as defensive armor, the only evidence of 

 dermal scutes or scales in any member of the fauna above the fishes is found 

 is Pantylas brcvlspinatus Williston, and certain loose scutes not yet referred 



» Newman, American Naturalist, vol. 47, p. 516, 1913. 



