24 
No crocodilian remains are known at present from the lowest Cre- 
taceous series. But the upper Greensand of New Jersey, U.S.A., 
has yielded Ayfosaurus with bi-concave vertebrae and two genera 
Thoracosaurus and Hylops with procelian characters. In Europe 
Gavialts macrorhynchus from the upper chalk of Maestricht differs 
very little from the recent species and thus foreshadows the exist- 
ing crocodilia. 
In the succeeding Tertiary Rocks numerous remains of fossil 
crocodilia have been discovered in the earliest Eocene deposits of 
England and the continent of Europe, differing very slightly from 
existing species. But there is a most remarkable feature in these 
deposits. Gavials, alligators, and crocodiles are often found asso- 
ciated together, whereas to-day all three of them occur widely sepa- 
rated in various parts of the world. In the London and Hamp- 
shire basins one gavial, two crocodiles, and one alligator have 
been found, and in this County the Bracklesham beds contained 
several species of crocodilia. These later species as well as the 
now living forms have undergone a great change, especially in the 
vertebral column. Each component vertebra, instead of being 
cupped at both ends as found in the earliest of the crocodilia, had 
a cup-and-a-ball structure. The defensive armour has also degene- 
rated, bony ventral scutes are exceptional and the dorsal ones 
fewer and thinner, not so closely arranged nor so firmly connected 
together, therefore adding less weight to the body. — Crocodilus 
Hlastingsie from the middle Eocene of Hordwell Cliff, Hampshire, 
had a peculiar dentition, half alligator and part crocodile, and a 
closer fitting armour than its contemporaries, resembling in that 
respect the South American caimans and jacares, the only two 
living species of alligators possessing bony ventral scutes as well as 
dorsal ones. But neither of the above-named species, nor any 
warrior of olden times, equalled the armature of the extinct 
Gontopholis crassidens of the Wealden, with its peg and groove 
tight-fitting cuirass. 
All the large carnivorous reptilia, /chthyosaurtt Mososaurit, 
and other large genera became extinct at the close of the Creta- 
ceous period, so the crocodilia existing at that time would have no 
powerful enemies to contend with. There was a concurrent 
diminution in the thickness of the dermal armour. As previously 
noticed, the vertebral column in all crocodilia prior to the upper 
Cretaceous was composed of bi-concave vertebree. In the upper 
Cretaceous the cup-and-ball modification first appeared and_ulti- 
mately prevailed. All existing crocodilia have the procelian char- 
acter. This strengthening of the vertebrae undoubtedly facilitated 
the progression of the reptiles on land in pursuit of the numerous 
forms of warm-blooded animals which made their appearance to- 
wards the close of the Cretaceous, and in the earliest Eocene 
period had increased in size and become very abundant. 
