Wieland has fitly named him, a creature a dozen feet or more in length, with a head a full yard long, while in the shallows prowled great fishes with massive jaws and teeth like spikes. [Illustration: Fig. 10.--Jaw of a Mosasaur, Showing the Joint that Increased the Swallowing Capacity of that Reptile.] There, too, was the great, toothed diver, Hesperornis (see page 83), while over the waters flew pterodactyls, with a spread of wing of twenty feet, largest of all flying creatures; and, not improbably--nay, very probably--fish-eaters, too; and when each and all of these were seeking their dinners, there were troublous times for the small fry in that old Kansan sea. And then there came a change; to the south, to the west, to the north, the land was imperceptibly but surely rising, perhaps only an inch or two in a century, but still rising, until "The Ocean in which flourished this abundant and vigorous life was at last completely inclosed on the west by elevations of sea-bottom, so that it only communicated with the Atlantic and Pacific at the Gulf of Mexico and the Arctic Sea." The continued elevation of both eastern and western shores contracted its area, and when ridges of the sea-bottom reached the surface, forming long, low bars, parts of the water-area were included, and connection with salt-water prevented. Thus were the living beings imprisoned and subjected to many new risks to life. The stronger could more readily capture the weaker, while the fishes would gradually perish through the constant freshening of the water. With the death of any considerable class, the balance of food-supply would be lost, and many large species would disappear from the scene. The most omnivorous and enduring would longest resist the approach of starvation, but would finally yield to inexorable fate--the last one caught by the shifting bottom among shallow pools, from which his exhausted energies could not extricate him.[5] [5] _Cope: "The Vertebrata of the Cretaceous Formations of the West," p. 50, being the "Report of the United States Geological Survey of the Territories," Vol. II._