44$ CROCODILIA CHAP. 



The age to which Crocodiles can live is quite beyond calcula- 

 tion. They are capable of propagation long before they are 

 anything like half-grown, maybe at an age of little more than 

 ten years ; then they continue to grow perhaps for more than 

 one hundred years, until they die. 



It is customary to divide the Eusuchia, most of which are 

 extinct, into a longirostral and a brevirostral section. In the former 

 the snout is much elongated and narrow, and the nasal bones, 

 although they are sometimes very long, do not reach the nasal 

 groove. The mandibular symphysis is very long, and is formed 

 not only by the dentary but also by the splenial bones. In the 

 brevirostral section the snout is shorter, sometimes broad and 

 rounded off, and the nasal bones are supposed to reach the nasal 

 groove, or at least to approach it very nearly ; the mandibular sym- 

 physis is formed by the dentaries only. But these distinctions 

 are quite arbitrary, and there exist all kinds of intermediate 

 forms. For instance, in Goniopholis and Diplocynodon, which 

 are both undoubtedly near allies of the recent Crocodiles and 

 Alligators, the nasal bones are considerably removed from the 

 nasal groove ; and in Crocodilus cataphractus they are separated 

 even from the premaxilla by the medio- dorsal suture of the 

 maxillaries. Again, in Gonioplwlis the mandibular symphysis 

 is so long that it comprises part of the splenial bones. Both 

 typically long- and short-snouted forms occur already in the 

 Upper Oolite, but in the Lower Jurassic age only long-snouted 

 kinds seem to have existed. The latter cannot easily be con- 

 nected with Belodon, one of the Parasuchia, on account of the 

 position of the nostrils; the mere shortening of the long 

 premaxillaries of Belodon would not transfer its distinctly 

 paired nostrils to the anterior end of the premaxilla. To 

 account for the position of the nasal groove in the Eusuchia, 

 we have to go back to a primitive condition, such as that of 

 the Pseudosuchian Aetosaurus, and this consideration shows that 

 the Parasuchia and Eusuchia are collateral branches. 



The Eusuchia have been split into many families. Zittel, 

 for instance, divides them into ten, some of them on insufficient 

 grounds, since there are too many intermediate forms ; and more, 

 sometimes quite unexpected, modifications are still being found. 

 Several of the accepted families represent collateral or con- 

 vergent lines of development. There is the same tendency to 



