The heavy armour of the head of the _Triceratops_ must have been developed for purposes of attack and defence, but we do not know whether it was for fighting their own species or for protection against the carnivorous reptiles. "So long," says Professor F. A. Lucas, "as _Triceratops_ faced an adversary he must have been practically invulnerable, but, as he was the largest animal of his time, it is probable that his combats were mainly with those of his own kind, and the subject of dispute some fair female upon whom rival suitors had cast covetous eyes. What a sight it would have been to have seen two of these big brutes in mortal combat, as they charged upon each other with all the impetus to be derived from ten tons of infuriate flesh! We may picture to ourselves horn clashing upon horn, or glancing from each bony shield until some skilful stroke or unlucky slip placed one combatant at the mercy of his adversary.... "A pair of Triceratops's horns in the National Museum (at Washington) bears witness to such encounters, for one is broken midway between tip and base; and that it was broken during life is evident from the fact that the stump is healed and rounded over, while the size of the horns shows that their owner reached a ripe old age." In connection with the concluding part of the last sentence it should be mentioned that reptiles, like fishes, but unlike birds and mammals, continue to grow throughout their entire span of life, so that unusually large bodily size is, at all events as a rule, an indication of advanced age. As regards general appearance _Triceratops_ may, perhaps, be best described as a reptilian rhinoceros, with the proviso that the tail was much larger and thicker than in that group of animals, and passed insensibly into the body, as in reptiles generally, while the number and arrangement of the horns were different. The _Pterosaurs_, or flying reptiles, made, as we have said elsewhere, a great advance. Williston regards them as having come to excel all other flying vertebrate animals. Some attained a wing-spread of twenty feet, and they could fly far and fast. They were all short-tailed; some of them probably could scarcely walk, and the larger of them had no teeth. Their bills resembled those of modern birds, and they have been styled the kingfishers of the Cretaceous seas. Terrific to look upon, they were probably not very deadly animals except to small fishes. The lizards did not make much progress; but the snakes made their first appearance, though they remained small; and the mammals showed little progress from the forms which were found in the previous era of the Jurassic.