Hesperornithidae

Hesperornithidae is a family of extinct flightless birds that lived during the Paleogene period, approximately 66 to 23 million years ago. They are known from fossils found in North America, Europe, and Asia. Hesperornithes were characterized by their long, slender bodies, long necks, and long legs, which are adaptations for a semi-aquatic lifestyle. They had a large, flat beak with serrated edges, which they likely used for feeding on fish and other aquatic prey.

The family Hesperornithidae is divided into two subfamilies: Hesperornithinae and Enaliornithinae. Hesperornithinae includes the type genus Hesperornis, which was one of the largest known birds of the Paleogene, with a wingspan of up to 10 meters. Enaliornithinae includes the genus Enaliornis, which was smaller and more specialized for a semi-aquatic lifestyle.

Hesperornithes are thought to have gone extinct around the same time as the non-avian dinosaurs, suggesting that they may have been directly affected by the Cretaceous-Paleogene extinction event. However, the exact cause of their extinction is still debated. Some researchers have suggested that they may have been outcompeted by other birds that evolved during the Paleogene, while others have proposed that they may have been affected by changes in climate or sea level.

Despite their extinction, Hesperornithes have left a significant fossil record, which has provided valuable insights into the evolution of birds and their adaptations to different environments. They are also of interest to paleontologists and bird enthusiasts alike, due to their unique appearance and the challenges they faced as they adapted to life in the Paleogene world.