386 Mr. S. V. Wood on the Effects upon Animal Life 



the most important saurian ; but the teleosaurian, or amphicce- 

 lian form of Crocodile, perished with the other marine Sauria 

 with which it was by its structure of vertebra allied, whose habits 

 it probably shared, and probably drew its sustenance from 

 the same sources. The proccelian form, however, is and has 

 been, through all tertiary periods at least, fluviatile or estuarine in 

 its habits, and adapted by its vertebral column to sustain itself 

 on land, and, inhabiting rivers, to draw its food from more than 

 one source ; this form also, by burying itself in mud, sustains 

 periods of great drought by a species of hybernation, a habit 

 partially shared by the peculiar reptilian form of fish (the Lepi- 

 dosteus) which we find first appearing and in great abundance 

 in the eocene formations. 



These changes in animal life have been such as, reasoning 

 a priori } one might predicate as likely to result from a change 

 in geographical configuration from an alignement running north 

 and south, producing a humid climate and an interchange of 

 temperature between high and low latitudes, to an alignement 

 from east to west with the land-tracts accumulated chiefly in low 

 latitudes, producing a climate, not merely hot, but influenced by 

 monsoons, which brought alternate seasons of moisture and 

 aridity. Further, there is reason to infer that all the forms of 

 terrestrial mammalia which are peculiarly adapted by migratory 

 habits to obtain food in one region when, by the regular change 

 of seasons, it has failed in another, of which the Ruminantia are 

 the most striking example, have originated in that continent of 

 which the Europeo-Asiatic one is a part, and which I have desig- 

 nated as the post-cretaceous continent. 



The effect of the post-cretaceous changes upon reptile life, in 

 extinguishing entirely several important orders and suborders, 

 and nearly extinguishing others, was far greater than upon other 

 forms of life. It is true that our knowledge of secondary warm- 

 blooded life is as yet very limited ; but none of the remains of 

 that life hitherto obtained from secondary formations have been 

 referred to any order not existing at the present day. It thus 

 appears that the effect of the post- cretaceous changes upon animal 

 life is commensurate with the degree in which that life is depend- 

 ent upon climatal conditions. Reptilia at the present day are 

 the most dependent upon climate, while Mollusca, .Fish, and 

 Mammalia are almost entirely independent of it ; and the result 

 of this dependence is, if the view put forward in the next section, of 

 Australia being an isolated remnant of the secondary continents, 

 be well founded, the state of change presented by the land and 

 sea respectively of that country*. 



* Of the orders of Reptilia at present known from the cretaceous depo- 

 sits, viz. Enaliosauria, Pterosauria, Dinosauria, Crocodilia, Lacertilia, and 



