Timespan and Evolution
Ichthyornis fossils have been found in almost all levels of the Niobrara Chalk, from beds dating to the late Coniacian age (about 89 million years ago) to the Campanian age (about 85 million years ago). Even earlier remains attributed to Ichthyornis have been found in the Greenhorn Formation of Kansas, dating to the early Turonian age (about 93 million years ago), and the Cenomanian of Saskatchewan, dating to about 95 million years ago.
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