Hesperornis regalis

Hesperornis regalis was a large, flightless diving bird that lived during the Late Cretaceous period, inhabiting the Western Interior Seaway that covered much of central North America. It is one of the best-known Mesozoic birds and a classic example of a bird that evolved for an entirely aquatic lifestyle.

The species was described by the American paleontologist Othniel Charles Marsh in 1872, based on fossils collected from the Niobrara Chalk deposits of Kansas. Marsh was then in the midst of his famous fossil-collecting rivalry with Edward Drinker Cope known as the Bone Wars.

Yes, Hesperornis retained functional teeth set in grooves along its long beak, a feature absent in all modern birds but shared by some other Mesozoic bird lineages. The teeth were suited for gripping fish, which were likely its primary prey.

Hesperornis had powerful hind limbs adapted for efficient underwater propulsion but its forelimbs were reduced to vestigial structures, making it poorly suited for movement on land. It likely spent almost its entire life in water, coming ashore only to nest.