Page:Popular Science Monthly Volume 73.djvu/565

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fierce scuttling rush out upon its prey, perhaps some slow-moving reptile or amphibian, perhaps even some smaller individual of its own kind, for there is ample evidence that these animals waged fierce battles among themselves. It is not uncommon to find bones which have been broken during life and healed again, telling of furious reptilian contests in the struggle for mates or for territory, or perhaps with the single idea of a cannibalistic meal.

But a more wonderful animal still has left its remains in the rocks. In this form there were high spines on the back, but instead of the spines being simple they were furnished with projecting processes on the sides, not unlike the yard-arms of the old-fashioned sailing ships. This resemblance led Cope to call the animal Naosaurus, ship-lizard. In a recent restoration of Naosaurus it has been given the skull of the fiercely carnivorous Dimetrodon, the general similarity of the forms

PSM V73 D565 Anterior portion of a dimetrodon jaw.png

Fig. 4. Anterior Portion of the Jaw of Dimetrodon, showing the great tusks.

seemed to warrant this, but recent discoveries have made it probable that Naosaurus was not an eater of flesh, but a peaceful, sluggish eater of shell fish and perhaps of vegetation. This animal has perhaps the most wonderful dentition of any known animal the incisor teeth are sharp and chisel-shaped, such as might be useful in cutting strong vegetation; behind these are five sharp triangular cutting teeth, not unlike the sectorial teeth of such flesh eaters as the tiger and lion; behind these are simple cones, such as would be useful in holding a struggling victim. But most wonderful of all, on the palate and in a corresponding position on the lower jaw were heavy plates of bone, covered by short stumpy teeth, such as occur in the jaws of fish which live upon molluscs. The animal was seemingly omnivorous, but instead of having a dentition of a generalized pattern like that of the pig or the human being, there was a set for each kind of diet. The