Enaliornis

Enaliornis was a genus of Cretaceous swimming birds found in England's Greensand formations. These birds are related to Hesperornis and are named from the Greek word for "of the sea".1

The Cretaceous Period (145.5 to 99.6 million years ago) was a significant time for avian evolution. During this period, two main groups of early birds diversified: the Enantiornithines and the Odontornithes. Enaliornis belongs to the latter group, which includes Hesperornis. Hesperornis was a large, flightless diving bird that lived in what is now the Great Plains region of the United States. It had teeth in its jaws, indicating that the horny beak of modern birds had not yet evolved. Its wings were small and useless for flight, but its legs were powerful and adapted for swimming.23