840 LIFE : OUTLINES OF GENERAL BIOLOGY 



fishes, that it bolted its food, that it depended chiefly on fishes and 

 cuttlefishes, and found the chitinous beaks of the latter more difficult 

 to digest than the bones of the former. Not less remarkable is the 

 ocular demonstration of the fact that Ichthyosaurs were viviparous, 

 bringing forth their young ones as miniatures of themselves. This is 

 very well shown by some specimens in the Stuttgart Museum, where 

 the unborn fossil offspring are conspicuous inside the fossil mother. 

 Thus the dead bones live ! 



The York Museum has amongst others a fine specimen of Ich- 

 thyosaurus crassimanus, which must have been about 30 feet long. 

 It shows very clearly that the ordinary long bones of the limbs are 

 in fish-Uzards very short, the main part of the paddle being the hand 

 or the foot. We counted the finger-joints on the paddle, and one 

 had nine, instead of the usual three ; and in some cases the number 

 rises to twenty! In all probability the chief swimming organ was 

 the posterior body, including the tail, the paddles being used chiefly 

 for steering and balancing. It was not advantageous that the paddles 

 should be long, but they retained great developmental vigour, which 

 found staccato expression in a multiplication of finger-joints. 

 Sometimes, moreover, the third digit has divided longitudinally in 

 the course of development, so that the number rises to six. 



Lung-breathing animals could not begin in the sea, so we must 

 look for the ancestors of fish-lizards among extinct terrestrial 

 reptiles. In the yard-long Mixosaurus the limb is not so paddlelike 

 as in typical forms; the teeth are not in a continuous groove; and 

 the vertebral column is not bent down into the tail as much as 

 usual. Even in regard to the peculiarly isolated Ichthyosaurs, 

 evolution proves itself. 



Jurassic. — During part of the Jurassic Period there seems to 

 have been a milder and more humid climate, with swampy stretches 

 along the shores of shallow seas, and an abundant vegetation, partly 

 consisting of seed-plants. It was probably in these rank meadows 

 that some of the giant reptiles found sustenance, enjoying a some- 

 what hippopotamus-like semi-aquatic life. 



In inland sun-baked stretches, rising into cliffs, there was a welter 

 of more active reptiles, illustrating evolutionary radiation in many 

 directions, and including some "flying dragons", such as Rhampho- 

 rhynchus, with a skin-wing outstretched on an enormously elongated 

 fourth finger. Not related to them and destined to be more successful 

 were the pioneer birds, but the Jurassic Archaeopteryx is already 

 too specialised to have been the first representative of the class. 

 There is no real difficulty in the fact that the first known fossil 

 mammal is Triassic, while the first known fossil bird is Jurassic. 

 Birds and mammals are on quite different evolution paths, diverging 

 from different reptilian origins. 



Cretaceous. — The beginning of the Mesozoic (or Geological 



