136 E. C. Case — AmjpJiibian Fauna at Linton^ Ohio. 



they Had lost their limbs. Some hid for safety in dark holes 

 and corners, others lurked in the slime, feeding on carrion or 

 the less active and well protected forms ; still others flashed 

 through the water in active pursuit of prey and dared give 

 battle in their conscious strength. It was a fauna whose ele- 

 ments occupied all the possibilities of the pool to preserve their 

 lives and propagate their kind, but there is an almost total lack 

 of bizarre and overspecialized forms, none heavily armored and 

 none with an excessive development of tusk or talon or spine, 

 and none that could be called giants of their kind. There was 

 a full occupation of all the reasonable possibilities of life but 

 nothing that w^ould indicate an extreme adaptation, either for 

 offense or defense, to limited paths of life such as occur in other 

 places and in other geological formations where the members 

 of the faunas were very perfectly adjusted to each other. 

 There was only the healthy growth induced by competition in 

 a fauna which still retained all the resilience of its juvenile 

 stage. 



Such an assemblage existing under very powerful stress, if 

 even from a single source, was full of the possibilities of devel- 

 opment ; ripe for the rapid and wide radiation in habits and 

 structures long denied them b}^ the monotony of their environ- 

 ment. For the animals in such a pool there were but two 

 possible endings. Either the pool would become choked by 

 the growing vegetation of the surrounding swamp, or in the 

 many fluctuations of the land, channels would open whereby 

 the animals could escape into other habitats and encounter a 

 new environment. It was apparently the first of these fates 

 which came to the Linton fauna. It was overcome in its full 

 vigor before the ultimate adjustments of life to life had pro- 

 duced the extreme development of armor and weapons of 

 attack seen in more mature or in senile faunas. Elsewhere in 

 the same region similar faunas were released to expend in 

 morphological advances and various adaptations to new condi- 

 tions the stored up stresses of similar periods of isolation. 



University of Michigan, 

 Ann Arbor, Mich. 



