"Ichthyornis" is notable primarily for its combination of vertebrae which are concave both in front and back (similar to some fish, which is where it gets its name) and several more subtle features of its skeleton which set it apart from its close relatives. "Ichthyornis" is perhaps most well known for its teeth. The teeth were present only in the middle portion of the upper and lower jaws. The jaw tips had no teeth and were covered in a beak. The beak of "Ichthyornis", like the hesperornithids, was compound and made up of several distinct plates, similar to the beak of an albatross, rather than a single sheet of keratin as in most modern birds. The teeth were more flattened than the rounded teeth found in crocodilians, though they became wider towards the base of the crown. The tips of the teeth were curved backward and lacked any serrations.