Tytthostonyx is a genus of prehistoric seabird.

Found in the much-debated Hornerstown Formation which straddles the Cretaceous–Paleogene boundary 66 million years ago, this animal was apparently closely related to the ancestor of some modern birds, such as Procellariiformes and/or "Pelecaniformes".

A single species is placed herein, Tytthostonyx glauconiticus.

[1] It has been placed into a family of its own, Tytthostonychidae.

This prehistoric bird article is a stub.