ii8 



WATER REPTILES OF THE PAST AND PRESENT 



fingers 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 generaUzed 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 finger or one toe in each Hmb. 



Fig. 56. — ^Front paddle of 

 thalmosaurus (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 finger and toe bones, 

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

 the adaptations to water Mfe, 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 



