Hesperornis was a prehistoric bird that lived during the late Cretaceous period, around 70 million years ago. It was a flightless bird, known for its aquatic lifestyle, resembling modern-day penguins. Hesperornis had a streamlined body, strong legs, and webbed feet, which made it an excellent swimmer. This bird was about 3 to 4 feet long and had sharp teeth, indicating it primarily fed on fish. Fossils of Hesperornis have been found in North America, providing valuable insights into the evolution of birds and their adaptation to life in water.