The second order of Toothed-birds (the Ichthyornithiformes) differs essentially from the first, as already mentioned, in having the numerous teeth implanted in distinct sockets. They take their name from Ichthyornis, the principal genus, which signifies “fish bird,”from the fact that the vertebrae are of the same shape as in fishes. Although a dozen or more nominal species have been described, disposed among five more or less tentative genera, the group is still imperfectly understood. Of the various members Ichthyornis victor is best known and may be selected for brief description. It was a much smaller bird than Hesperornis, being about the size of a common Pigeon, and was clearly a very powerful flyer. The head was relatively much larger than in Hesperornis, but the disposition of the teeth was the same in both, and the component parts of the mandibles were likewise distinct. The teeth were all sharp and pointed, more or less compressed, and strongly recurved, and were placed vertically as in the crocodiles and certain extinct lizards. The exact number of vertebrle in the neck is not known, but from the large number found it is presumed that they were numerous, and that the neck was relatively long and slender. The undoubted strong power of flight enjoyed by Ichthyornis is well indicated by the shoulder girdle and wings, these conforming strictly to the type seen in strongly keeled living birds, and as has been said, “might have been used by some existing birds with strong powers of flight.” The legs and feet are of small size and present no particular features that may not be observed in modern flying birds. The following account of the probable mode of life and habits of Ichthyornis is from Marsh, the original describer of the bird: “The sharp cutting teeth of Ichthyornis prove, beyond a doubt, that it was carnivorous; its great power of flight, long jaws, and its recurved teeth suggest, moreover, that it captured its prey alive. Its food was probably fishes, as their remains are found in great abundance mingled with those of Ichthyornis. These fossils occur in the bed of the old Cretaceous ocean in which Hesperornis swam. Both of these birds were clearly aquatic in habit, as shown by various points in their structure, and the conditions under which their remains were deposited. In many respects, Ichthyornis probably resembled the modern Terns in its mode of life. The powerful feet and wings suggest similar habits in flight and rest.”
The affinities of Ichthyornis are almost as much in question as those of Hesperornis. By some it is regarded as being nearest to the Terns and especially the Skimmers, by others it is relegated to the vicinity of the Storks and Plovers, while still others would place it between the Ducks and Accipitres. The truth of the matter is its structure is still too imperfectly known to venture a positive opinion, and even if we were familiar with all the details of its anatomy, it is probable that its direct relationship with modern birds would still be as difficult to establish, for it appears to have belonged, together with its allies, the other Toothed-birds, to a group that represents one link in the chain of succession between reptiles and present birds.