ICHTHYORNIS
With its feathered body, powerful wings and keeled breastbone, Ichthyornis, ("fish bird") must have looked and acted like a plump tern. The mouth was armed with backwardly curved teeth which did not reach the front of the upper jaws; the lower jaws had extra joints which allowed them to open widely like the jaws of mosasaurs, with which they have sometimes been confused.

Though the various species of Ichthyornis stood only 6 to 9 inches high, they were apparently able to swallow thick-bodied fish.

HESPERORNIS
Very little is known about Cretaceous birds, for their remains are fragmentary and rare. Hesperornis ("western bird") had very large feet, diminutive wings and a flat unkeeled sternum, thus indicating that it could not fly. Its legs were turned backward so far they could only be used for swimming. The articulation of the lower jaw was similar to that of the mosasaur, including sharp teeth.

Hesperornis had no need for wings or walking legs as long as it stayed in the water. There it lived like an oversized, flightless loon, skimming over the surface, diving, and swimming long distances while submerged. It could easily capture small fish while dodging carnivorous reptiles that might have fed upon it Hesperornis probably nested on isolated islands or it is possible that it gave birth to live young and never ventured onto dry land.