In Theriosuchus the breadth and shortness of the antorbital part of the skull, in proportion to the part behind, exceeds that in any modern broad-snouted Crocodile. Even in the young 'Crocodile à deux arrêtes,' figured in plate i. of Cuvier's 'Ossemens Fossiles'[1], a transverse line across the fore part of the orbits equally bisects the skull, omitting the mandible. In Theriosuchus the same line leaves in advance six thirteenth parts of the length of the skull.
This proportion suggested at first view the immature state of the individual. But of the numerous evidences of Theriosuchus pusillus, none were larger than those figured in Plate IX., and several other fragmentary evidences of the species had come from still smaller individuals.
I conclude, therefore, that, as in the case of most species notable for their diminutive size, immature characters of the larger species of the genus are associated with such dwarfishness of the adults.
I estimate the average length of a mature Theriosuchus at 18 inches. The length of the skull, taken as that of the mandible, is 3 inches 6 lines. In the articulated skeleton of a modern Crocodile the angle of the lower jaw extends to the third cervical vertebra. In Alligator lucius the trunk, from the third cervical to the last sacral vertebra inclusive, is nearly equal to two lengths of the skull; the length of the tail is 213 lengths of the skull. The trunk of Theriosuchus, so defined, includes two lengths of the skull; the tail, as indicated by a portion of skeleton preserved, equalled 213 lengths of the skull. In the long-jawed Gavials and Teleosaurs the trunk includes about 114 length of the skull; but the tail is proportionally longer than in the short- and thick-jawed Crocodiles.
The actions and consequences of a Theriosuchus submerged with "a warm-blooded animal" of the size of a shrew or rat in its mouth might not excite the physiologist to analyze results and relations to palato-narial arrangements. The case is otherwise with a "large and powerful mammalian quadruped" in that predicament; its amphibious captor would not escape choking by the mere "closure of the external nostrils."
Let any F.G.S., with his head under water, hold his nose and open his mouth, and he will experience some trouble at the glottis.
The exclusion of water from the lungs is truly the important matter; and I fear my allusion to the mechanism for that purpose, which is peculiar to the Neozoic Crocodiles[2], was too brief to dispel a possible haziness of conception of such mechanism.
A Crocodile, having seized and submerged a tiger or a buffalo, admits the water into its wide unlabiate mouth by the spaces to which the thickness of the part gripped keeps asunder the upper and the lower jaws. Thus the part of the mouth not occupied by the prey is filled with the fluid in which the mammal is being dragged and drowned.
