286 ANNALS NEW YORK ACADEMY OF SCIEXCEt< 



have amphicoelous vertebrae, whereas all Cenozoic and late Cretaeic croco- 

 diles have procoelous vertebras. It is commonly believed that certain of 

 the narrow-snouted types (Teleosaurus) led into the <ravials. tlie l)road- 

 snouted (Goniopholids) into crocodiles and alligators; and that the 

 broad-snouted types lirst appearing in the Upper Jura are derived from 

 the teleosaurs which first appear in the^MJddle Jura. Neither of these 

 propositions seems to me to be probable. The narrow-snouted crocodiles 

 are characteristic of marine or semi-marine formations, the broad-snouted 

 kinds of fresh-water formations; the known formations of the Middle 

 Jurassic are chiefly marine, those of the Upper Jura chiefly fresh-water. 



If we turn back to the Trias, we find that in the allied Parasuchia 

 there were also long-snouted {Mystriosuclius and Rutiodon) and broader- 

 snouted (Belodon) types — both of fresh-water habitat, but apparently 

 less aquatic than Crocodilia; in the allied Pseudosuchia the snout was 

 short, and the adaptation to amphibious or fresh-water life; wliile the 

 more distantly related dinosaurs were terrestrial and short-snouted. 

 Upon these data, it appears to me more reasonable to suppose that the 

 Triassic Mystriosuchus and Rutiodon, the Jurassic Geosauridae, Teleo- 

 sauridse and Metriorhynchidaj and the Tertiary Gavialidge are all inde- 

 pendent successive adaptations to a fish-eating diet and a more or less 

 marine habitat and that 1:he Jurassic Goniopliolida? are the source of all 

 the modern Crocodilia. This will also relieve us from the necessity of 

 supposing that procoelous vertebrte and a number of other identical char- 

 acters were independently and simultaneously acquired in two phyla of 

 diverging adaptation. The accepted view involves the anomaly of asso- 

 ciating divergent adaptation with convergent structural evolution. 



However this may be, we are justified in assuming certain characters 

 as primitive among the modern Crocodilia, since they are common to all 

 the older types. These are the following: 



1) More complete and consolidated ventral armature. Common to all the 

 Mesozoic genera, retained in Diplocynodon of the European Tertiary and the 

 modern Caiman and OstcoUrmus. 



2) A notch instead of a pit in the upper jaw for reception of the lower 

 canine. Common to nl! the short-snouted crocodiles of the Mesozoic and Ter- 

 tiary, retained in the modern Crocodilus. 



3) Amphioo'lous vertebne. Common to all Crocodilia and related groups up 

 to the middle Cretaceous, lost in most Upper Cretaceous and all Tertiary"* 

 and modern genera. 



4) Large supratemporal and small lateral temporal fenestne. The upper 

 temporal fenestra is large in all Mesozoic Crocodilia, considerably smaller in 

 the gavials, quite small in Crocodilus, Alligator and Caiman. 



"8 Except Not OS II eh tin of the Patagonlan Eocene. 



