Fig. 142a.—Head of Pliosaurus. Jurassic. Much reduced.
Fig. 142b.—Paddle of Plesiosaurus Oxoniensis. Jurassic.—After Phillips. One-tenth natural size.
Another remarkable group is that to which Cope has given the name of Pythonomorpha, and which he regards as allied to the serpents, or as gigantic sea-serpents provided with swimming paddles, but which Owen considers more nearly connected with the lizards. In either case they constitute a group by themselves, remarkable not only on account of their anatomical affinities with animals so unlike them in general port, but also for their enormously extended length and formidable dentition ([Fig. 143]). Such animals as the Mososaurus of Maestricht and Clidastes of Western America may have exceeded in length the largest Ichthyosaurs and the most bulky of living Cetaceans, though their slender forms and numerous vertebræ remind one of the semi-fabulous sea-serpent, rather than of any known animal of our modern age. They were characteristic of the Later Mesozoic, more especially of the Cretaceous period, and must have been formidable enemies to the fishes of their time.
Owen has formed two orders[66] for the reception of some remarkable extinct reptiles of this age, found especially in South Africa and India, but also in Europe and America. The first includes large lizard-like animals having horny jaws like those of turtles, and in some of the species with great defensive tusks ([Fig. 144]). Their mode of life is not well known, but they may have been peaceable and harmless vegetable feeders. The second has been already referred to, in connection with the Permian, where it first appears, though it is continued in the Trias ([Fig. 145]). The resemblance of the skulls of these creatures to those of Carnivorous mammals is very striking, and nothing can be more singular than their early appearance and their decadence before the advent of those Tertiary mammals which in more modern times occupy their place.
