''Iaceornis'' is a prehistoric marine bird genus endemic to

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

during the Late Cretaceous living about 83.5

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. It is known from a single fossil specimen found in Gove County, Kansas (USA), and consisting of a partial skeleton lacking a skull. Since it was first discovered by Othniel Charles Marsh in 1877, the specimen (YPM 1734) was long considered to belong to the contemporary species ''

Apatornis celer ''Apatornis'' is a genus of prehistoric birds endemic to North America during the late Cretaceous. It currently contains a single species, ''Apatornis celer'', which lived around the Santonian-Campanian boundary, dated to about 83.5 million years ...

''. 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 specimen of ''Apatornis''. Therefore, she assigned the more complete remains to a new genus and species, ''Iaceornis marshi'', meaning "Marsh's neglected bird".Clarke, J.A. (2004). "Morphology, phylogenetic taxonomy, and systematics of ''Ichthyornis'' and ''Apatornis'' (Avialae: Ornithurae)." ''Bulletin of the American Museum of Natural History'', 286: 1-179
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/ref> In Clarke's phylogenetic analysis, she found that ''Iaceornis'' is more advanced than '' Ichthyornis'' but less advanced than

modern bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

References

Bird genera Prehistoric ornithurans Late Cretaceous birds of North America {{paleo-bird-stub