Ichthyornithines

Ichthyornithines were a group of extinct, toothed birds that lived during the Late Cretaceous period. They are known primarily from fossils found in North America, particularly in deposits of the Niobrara Chalk. The most well-known genus is Ichthyornis, which gives the group its name. These birds resembled modern gulls in size and general appearance but possessed several primitive avian and reptilian features.

One of the most significant characteristics of ichthyornithines was their teeth. Unlike modern birds, which have beaks, ichthyornithines had jaws lined with small, sharp teeth. These teeth were set in distinct sockets, a feature common in many reptiles. Their skeletal anatomy also showed a mixture of bird-like and reptilian traits. For instance, they had a keeled sternum, which is an adaptation for flight muscles found in modern birds, indicating they were capable fliers. However, they retained unfused vertebrae in their neck and had a long bony tail, unlike the pygostyle of modern birds.

The diet of ichthyornithines likely consisted of fish and other small marine life, as suggested by their teeth and the marine environments where their fossils are found. They were likely agile swimmers and divers, utilizing their flight capabilities to hunt in coastal waters. The discovery of ichthyornithines was important in understanding the evolutionary transition between non-avian dinosaurs and modern birds, showcasing a stage where bird-like features were emerging alongside reptilian retentions. Their extinction occurred at the end of the Cretaceous period, likely due to the same mass extinction event that wiped out the non-avian dinosaurs.