''Iaceornis'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of marine ornithuran

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s closely related to modern birds. It was endemic to

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, living about 83.5 million years ago. It is known from a single fossil specimen found in

Gove County, Kansas Gove County is a county in the U.S. state of Kansas. Its county seat is Gove City, and its most populous city is Quinter. As of the 2020 census, the county population was 2,718. The county was named for Granville Gove, a captain of Compa ...

, and consisting of a partial skeleton lacking a skull. Since it was first discovered by

Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of paleontology. A prolific fossil collector, Marsh was one of the preeminent paleontologists of the nineteenth century. Among his legacies are the discovery or ...

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 A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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
PDF fulltext
/ref> In Clarke's

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis, she found that ''Iaceornis'' is more advanced than '' Ichthyornis'' but less advanced than modern birds.

References

Ornithurae Late Cretaceous dinosaurs of North America Fossil taxa described in 2004 {{Paleo-bird-stub