Hesperornithinae

Hesperornithinae is an extinct subfamily of flightless seabirds belonging to the order Hesperornithiformes. These birds are known from the Late Cretaceous period, primarily in North America. Hesperornithines were well-adapted to a marine environment, possessing adaptations for swimming and diving. Their most striking feature was their complete lack of wings; any ancestral wing structure had been reduced to vestigial knobs. This flightlessness, combined with their pelvic structure, suggests they were incapable of terrestrial locomotion and likely spent their entire lives in the water.

The diet of hesperornithines consisted of fish and other marine life, which they would have caught using their sharp, backward-pointing teeth housed in shallow grooves along the jaws, a feature not found in modern birds. Their skulls were also distinctive, with kinetic joints that allowed for a wide gape, enabling them to swallow large prey. Hesperornithinae included some of the largest hesperornithiforms, such as Hesperornis itself. They were part of a diverse marine ecosystem that existed before the Cretaceous-Paleogene extinction event, which ultimately led to their demise along with the non-avian dinosaurs. Fossil evidence indicates a predatory role in their ecosystem.