Enaliornis
Encyclopedia
Enaliornis is a 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...

 of hesperornithine 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...

 which lived in the late Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...

, making it the oldest known hesperornithine. Fossils have been found near Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...

, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. Due to its lack of certain hesperornithid apomorphies, they were much more "conventional" birds and were initially held to be Gaviiformes
Gaviiformes
Gaviiformes is an order of aquatic birds containing the loons or divers and their closest extinct relatives. Modern gaviiformes are found in many parts of North America and northern Eurasia , though prehistoric species were more widespread.-Classification and evolution:There are five living...

 (loons/divers).

Enaliornis was originally named Pelagornis
Pelagornis
Pelagornis is a widely-known genus of the prehistoric pseudotooth birds. These were probably rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty....

('sea bird') by Seeley in 1866, but that name was preoccupied by a Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

 bird related to the pelican
Pelican
A pelican, derived from the Greek word πελεκυς pelekys is a large water bird with a large throat pouch, belonging to the bird family Pelecanidae....

s. Three species have been described: The small Enaliornis sedgwicki, the medium-sized Enaliornis seeleyi, and the large Enaliornis barretti. Together, they are the only birds currently assigned to the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Enaliornithidae. The presumed hesperornithine Potamornis
Potamornis
Potamornis is a prehistoric bird genus that dated back to the late Maastrichtian. Its scrappy remains were found in the Lance Formation at Buck Creek, USA, and a single species has been named and described in 2001: Potamornis skutchi....

from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

 Lance Formation
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...

 of Buck Creek (USA) may also be related to this group.
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