12 GUIDE TO THE FOSSIL REPTILES, AMPHIBIANS, FISHES. 
(WaH-cases 
2a, 3. 
Table-cases 
5-7. 
Wall-case 
3. 
Table-case 
8 . 
Table-cases 
9, 10. 
Wall-case 
3. 
Table-case 
11 . 
Greensand are of the typical concavo-convex pattern. All 
the Lower Cretaceous and Jurassic crocodiles, however, differ 
from those of more modern times in having the curious bony 
roof of the palate extending less far backwards, so that unless 
a soft piece of palate in their case was adapted to serve the 
same purpose as a plate of bone in the living crocodiles, they 
could not have kept their mouth open under water (compare 
Figs. 6 and 9). Their vertebrae were also more or less 
concave at both ends, not united by ball-and-socket joints ; 
and their whole skeleton in most cases suggests a more 
exclusively aquatic mode of life than that of the existing 
crocodiles. In fact, the only Mesosuchia (“ intermediate croco¬ 
diles ”)—as these reptiles are technically termed—which have 
the outward appearance of modern crocodiles and alligators, 
are a few obvious marsh-dwellers from the Wealden and 
Purbeek formations. Goniojpholis, with its broad head and 
powerful teeth, may well have preyed on land-animals 
which came to drink the water it haunted; while the dwarf 
Theriosuchus and Nannosuchus are associated in the Purbeek 
Beds with numerous small land-mammals which would form 
most suitable food. All these marsh-dwellers were well 
armoured above and below with the usual thick, pitted, 
bony scutes, of which those on the back were firmly united 
by peg-and-socket joints as in the scales of ganoid fishes. 
Many of these scutes are exhibited in the collection, and 
they are well displayed on the slab of Purbeek stone con¬ 
taining Goniopholis (Wall-case 3), which was originally in 
Dr. Mantell’s collection and excited much interest in 1839 
when he described it under the name of “the Swanage 
Crocodile.” 
The extreme adaptation of a crocodile for life in the sea 
is shown by Geosaurus and Metriorliynchus (Fig. 7) from 
European Upper Jurassic rocks. These reptiles have the 
usual elongated snout of an aquatic animal, with rather large, 
laterally compressed teeth in sockets; but the external bones, 
of the head are not much sculptured, some, indeed, being 
quite smooth. Their backbone turns sharply downwards at 
the end of the tail, and must originally have borne a vertical 
triangular tail-fin, like that of Ichthyosaurus. Their fore 
limbs are very small and in the form of paddles or flippers, 
while their hind limbs are crocodilian in shape, but relatively 
large for hard swimming. Bony plates are absent, so that 
the skin must have been as smooth as that of an Ichthyosaur, 
or porpoise. The original skull and other bones of Geosaurus 
