In Ichthyornis it is very small.
Of these the most interesting are Ichthyornis (= Graculavus) and Hesperornis, from the Cretaceous shales of Kansas.
P. 344) a second fossil bird from the same locality was indicated as Ichthyornis dispar- from the fish-like, biconcave form of its vertebrae.
On the other hand the Odontotormae, as exemplified in Ichthyornis, having the primitive biconcave vertebrae, yet possessed the highly specialized feature of teeth in distinct sockets.
Hesperornis too, with its keelless sternum, had aborted wings but strong legs and feet adapted for swimming, while Ichthyornis had a keeled sternum and powerful wings, but diminutive legs and feet.