260 TEN years' progress in vertebrate paleontology 



forms answering better as actual connecting links anywhere in vertebrate 

 paleontology than do the subaqiiatic Aigialosaurs of the Dalmatian 

 region, connecting the mosasaurs with terrestrial lizards. 



Among nearly every other order of the reptiles have new discoveries 

 and new interpretations thrown light on their evolution; the shortening 

 of the limb bones and peculiar modifications of the skull among pie- 

 si osaurs, the extreme specializations of the later pterodactyls, the pro- 

 gressive modifications, not numerous it is true, of the Chelonia, are too 

 numerous to describe in detail. The Parasuchia, by unanimous consent, 

 have been divorced from the Crocodilia, and much new light has been 

 thrown upon their relationships. The phytogeny of the Crocodilia has 

 been placed on a Ibetter foundation, and a remarkable new divergent 

 phylum, the Thalattosuchia, has thrown a flood of light on the evolution 

 of aquatic Amniota, helping to explain those resemblances that so long 

 seemed mysterious between -the ichthyosaurs, plesiosaurs, mosasaurs, croco- 

 diles, thalattosaurs, champsosaurs, mesosaurs, etcetera. Those adaptive 

 resemblances of the aquatic air-jjreathers, that made the whale a breathing 

 fish till the beginning of the last century and the ichthyosaurs real fish 

 reptiles till twenty years ago, are no longer seductive ; we have now a 

 clearer viewpoint here as in so many other places. Perhaps in no other 

 order has there been a wider and fuller accumulation of knowledge, 

 accurate knowledge, than among the dinosaurs. While in the end I do 

 not think that this knowledge has greatly modified the phylogenetic 

 conceptions of Marsh and Cope, it has at least excluded much of error. 



Especially has our knowledge of the early reptiles acquired in the past 

 few years thrown a flood of light on the evolution of the class, at least 

 in the revelation of earlier errors. The cotylosaurs and theromorph 

 reptiles have been brought into the most intimate relations, till their 

 separation has become a matter of the most trivial structural characters. 

 The connecting chain between the most generalized of reptiles, as rep- 

 resented by Seymouria, to the most generalized of mammals is now almost 

 coinplete : Jiowhere are there differences that in themselves are of more 

 than fAiiti'y value, perhaps not even tliat. That Ave attribute to rudi- 

 mentary temporal vacuities of Opliiacodon, or the vestigial quadrate of 

 the theviodonts ordinal or class values, is merely a matter of taxonomic 

 coQvenience. Classification will have attained its higliest perfection when 

 nothing more than specific differences are the final distinction between 

 families, orders, and classes. 



Among the birds not so much has been done perhaps in paleonto- 

 logical discovery as in the reinterpretation of the many accrued facts. 

 Perhaps no positive addition has been made to our knowledo:e of their 



