A GREAT PERMIAN DELTA 



5 6 3 



dorsal frill as anything but a hindrance to any 

 quick movement. Cope suggested, in a spirit of 

 fun, that these animals were the precursors of the 

 modern fin-keeled yacht and that when they 

 wished to navigate the Permian waters they swam 

 upon their backs. Other authors have suggested 

 equally abused uses in a similar spirit, but there 

 are very few that can be considered with any 

 degree of seriousness. The obvious suggestion is 

 that the spines served as some form of protective 

 mimicry, perhaps helping the animal to remain 

 concealed among the reeds which bordered the 

 lakes or streams, but this seems hardly necessary 

 when we reflect that the animal was the dominant 

 form of its time and needed no concealment unless 

 it was to aid in lying in wait or in making an 



unseen approach until 



Fig. 8. Side View 

 of Two Dorsal Ver- 

 COn- T ebr;e of Naosaurus. 



Fig. 7. Front View of 

 One of the Dorsal Spines 

 of Naosaurus. 



sufficiently near for the 

 final rush upon its un- 

 suspecting prey. This 

 last is perhaps a fair 

 suggestion, but it seems 

 that the physiological 

 burden of maintaining 

 such an essentially weak 

 structure must have far 

 outweighed any conceiv- 

 able advantage of 

 cealment. The spines 



i. 



were slender and were constantly subject to 

 fracture in battle or by accident and the ani- 

 mal must have expended no inconsiderable 

 portion of its energies in repairing the broken 

 structure. 



There remains the suggestion that the 

 spines are remnants of a formerly useful 

 structure and their present condition is 

 purely a physiological one due to overgrowth. 

 It seems certain that when a structure has 

 developed so far as to give an animal a great 

 advantage it may continue to grow until it 

 is rather a burden than a help. The structure 

 starting as a protective feature may give the 



