produced by great Geographical Changes. 3&o 



The disappearance of this great tetrabranchiate family affords, 

 I think, the clue to the disappearance of the secondary marine 

 saurians; while the development of the dibranchiate family has 

 been commensurate with that of the Cetacean order, of some of 

 which they form the food. The numerous family of Cestraciont 

 fishes must have been mainly dependent upon a copious supply 

 of mollusca for their food; and this most probably consisted 

 mainly of the tetrabranchiate Cephalopoda, the means for the 

 crushing of whose dense shells were afforded by the palate or 

 tubercle teeth of these fishes. We may not unreasonably infer 

 that the habits of fish feeding upon nearly stationary food, such 

 as mollusca, would, unlike those of the Squalidse, which now feed 

 upon fish, have been sluggish. The marine Saurians, again, we 

 may infer, procured their food from fish, and from those forms 

 among them whose sluggish habits admitted of the easiest capture. 

 Now the disappearance of the Tetrabranchiata, of the Cestra- 

 cionts, and of the marine Saurians, was contemporaneous ; and 

 we can hardly refuse to admit that such a triple destruction 

 must have arisen either from some common cause, or from these 

 forms being successively dependent for existence upon each 

 other. The habits of existing Squalidse show that that order is 

 not unsuited to a wide range remote from the shores, and thus 

 independent of causes operating upon ■ coast followers. The 

 Squalidse survived the post-cretaceous changes ; but of the shore- 

 followers existing at the cretaceous epoch, all the marine Sauria, 

 all the Tetrabranchiata except the Nautilus and Aturia, and 

 all the Cestracionts except the one-surviving Australian genus, 

 perished between the cretaceous and the eocene epochs. 



The changes of condition resulting from such an alteration in 

 the geographical distribution as I have endeavoured to trace 

 would, I conceive, by no means be confined to the marine fauna ; 

 its effects upon the Dinosaurian family by means of the extremes 

 of aridity alternating with wet seasons, produced by monsoons 

 parching up vegetation periodically, may be imagined if we 

 reflect upon the prodigious amount of food required by the her- 

 bivorous forms of this order, and that the extinction of the her- 

 bivorous Dinosauria would involve that of the carnivorous. It is 

 just those forms of Sauria which are suited to sustain these alter- 

 nations of moisture and aridity which did survive the post-creta- 

 ceous changes, and still endure. The proccelian vertebrate form 

 of Crocodile, which makes its appearance in the cretaceous de- 

 posits, has been throughout all the tertiary periods, and still is, 



notably iu the case of the coral reefs, which occur almost exclusively on 

 the eastern shores of the existing continents, although why this should be 

 so we as yet know not. 



Phil Mag. S. 4. Vol. 23. No. 155. May 1862. 2 P 



