n8 



WATER REPTILES OF THE PAST AND PRESENT 



lingers and toes it is an equal impossibility. All naturalists are now 

 agreed that a specialized character can never revert to a generalized 

 condition, or rather to a generalized structure, that an organ once 

 functionally lost can never be regained by descendants. A char- 

 acter once lost is lost foreover; horses of the future can never have 

 more than one linger or one toe in each limb. 



W-nh 



Fig. 56. — Front paddle of Oph- 

 tkalmosaurus (after Andrews) : h, 

 humerus; r, radius; u, ulna; p, 

 pisiform; re, radiale; int, inter- 

 medium; ue, ulnare. 



Fig. 57. — Front paddle of Mer- 

 riamia, a Triassic ichthyosaur. 

 (After Merriam.) Explanations 

 as in Fig. 56. 



And there was an increase in the ichthyosaurs, in some not 

 only of the number of digits in each limb, but in all of the number 

 of bones in each digit, a character found also in the unrelated 

 mosasaurs and plesiosaurs. This increase in linger and toe bones, 

 or hyperphalangy as it is called, is one of the most peculiar of all 

 the adaptations to water life, changing the feet and hands from 

 the ordinary walking type to the fish-like swimming type. The 

 bones beyond the humerus and femur in the ichthyosaurs were so 



