Iaceornis is a prehistoric marine bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 endemic to North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 during the Late Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 living about 83.5 mya. It is known from a single fossil specimen consisting of a partial skeleton lacking a skull. Since it was first discovered by Othniel Charles Marsh

Othniel Charles Marsh

Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...

 in 1877, the specimen (YPM 1734) was long considered to belong to the contemporary species Apatornis celer. Because it is relatively complete, most discussions of Apatornis actually focused on the Iaceornis fossil. In 2004, paleontologist Julia A. Clarke showed that the skeleton actually differed in important characteristics of the wing bones from the true, holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 specimen of Apatornis. Therefore, she assigned the more complete remains to a new genus and species, Iaceornis marshi, meaning "Marsh's neglected bird".

In Clarke's phylogenetic analysis, she found that Iaceornis is more advanced than Ichthyornis

Ichthyornis

Ichthyornis is a genus of toothed seabirds from the Late Cretaceous of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway during the Turonian-Campanian ages,...

but less advanced than modern birds.