THE AGE OF REPTILES 



task of providing food for such a body must have been a 

 severe tax on so small a head. The inconvenience of its 

 bulkiness was perhaps reduced by living in and about 

 water ; but from the excellent preservation of some of the 

 skeletons it has been thought that its life was often ended 

 by sinking in some quicksand or shoal, from which its own 

 massiveness forbade that the Brontosaurus should extricate 

 itself. 



Not greatly removed in habit or appearance from the 

 Brontosaurus was the Diplodocus, a magnificent specimen 

 of which has been set up in Pittsburg, and a fine replica, 

 owing to the generosity of Mr. Andrew Carnegie, in the 

 Natural History Museum. The Diplodocus, a harmless 

 placid beast, was over eighty feet from the tip of his snout 

 to the end of his enormous tail. It has been calculated that 

 impulses travel along the nerves to the brain at the rate 

 of about twelve yards a second. The rate may have been 

 less in the case of the sluggish Diplodocus, but in any case 

 it would evidently take at least two seconds for a nerve 

 impulse to travel the length of this reptile ; so that if any 

 enemy attacked him at the end of his tail it would be two 

 seconds before the Diplodocus would realise the fact, and 

 perhaps four seconds before he could begin to turn round 

 to defend himself. Even larger than these was the tre- 

 mendous BrachiosauruS) who weighed as much as a steam- 

 engine and whose thigh-bone was nearly eight feet high. 

 These were the largest reptiles ever known, and may be 

 taken as reaching the point when bulk becomes a burden, 

 and as signalising an approach to the limit of evolu- 

 tion in the line of size. Less bulky than these were the 

 Q 241 



