The Story of the Roclcs 



137 



mens, which are therefore on exactly the same scale. 

 The single dinosanrian tooth p-ceatly exceeds not only 

 the tooth of the nianniial, but the (•< ntaininj; jaw or 

 even the entire creature as the imaj>ination conjure.-; it 

 up. "2 



As to the cause of mammalian development we can again 

 only conjecture. Lull has suggested that increasing dryness 

 of climate and corresponding desert conditions, necessitar- 

 ing speed on the part of animals in search of food and water, 

 or in flight from their enemies, coupled with the extensive 

 glaciation in the Southern hemisphere in late Palaeozoic times, 



Tooth of a Dinosaur Compared with the Jaw of a Coxtempuraky 



Mammal 



From Lull 's ' ' Organic Evolution. ' ' 

 Courtesji of Professor Lull mid tlit' Miicmilhiii ComiJiniii. 



which glaciation would mean increasing cold and the nred 

 of a furry covering, were the inciting causes. But apart 

 from the fact that this explanation implies, if it does not 

 state, an acceptance of Lamarck's doctrine, which at the 

 present time is in the discard with most zoologists, is the 

 further fact that the succeeding or Mesozoic era was one 

 which witnessed the remarkable development of reptiles, 

 which are distinctly types not adapted to aridity and cold- 

 ness of climate. Perhaps the best we can do after all, when, 

 as so frequently happens in pliilosophy and science, we find 



^Lull, "Evolution of the Earth," pp. 133-134. By permission of the 

 Yale University Press. 



