CRETACEOUS PERIOD 103 



teeth possibly as a result of racial old age. How far this 

 deprivation affected their fortunes cannot be determined. 

 Whatever the cause, they became practically extinct long 

 before the close of the Period. Their career had probably 

 been mainly in the shallows, where the competition of 

 younger life may in time have become too keen. As a forlorn 

 hope they may have migrated to deep waters, and in their 

 new sphere have been starved and persecuted out of exist- 

 ence. 



Plesiosaurs were also under great pressure ; but their PLESIO- 

 collapse came later than that of the fish-lizards. The short- SAURIANS 

 necked, sharp-toothed forms of Jurassic times had apparently 

 left no descendants (Pliosaurus) ; but plesiosaurs resembling 

 them at least as regards the teeth were in Cretaceous waters 

 (Polyptychodori). For a considerable time the long-necked 

 forms flourished greatly, and in many parts of the world ; 

 but they were submitted to severe tests in the latter part of 

 the Period. Even then, however, some forms with " record " 

 necks were to be seen. Elasmosaurus, for instance, had a 

 neck twenty-two feet in length. Many curiously modified 

 forms were also then in evidence. Some of these had long 

 heads, obtained apparently at the cost of the neck (Trina- 

 cromerum). In some animals the head exceeded the neck 

 in length (Dolichorhynchus). These modifications were, no 

 doubt, desperate attempts to meet changing conditions ; but 

 they proved of no permanent avail. Indeed they were prob- 

 ably reversions to a form of structure such as their far-back 

 unknown land-ancestors had possessed ; and manifestations 

 of atavism are not indicative of true energy. But however 

 that may have been, plesiosaurs, long-headed and short- 

 headed, and with necks of whatever length, were one and all 

 doomed. They were essentially creatures of old-fashioned 

 type, and without sufficient elasticity to be effectively trans- 

 formed. Difficulty in obtaining food, owing to the greater 

 wariness, keener sight, and better swimming powers developed 

 in fishes, may have been one of the causes which brought 

 about their downfall. As also may have been the increase of 

 large voracious fishes. But the closing portion of the Creta- 

 ceous is one of the darkest epochs in Geology ; and the 



