Zhylgaia 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 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...

s known only from fossils. Its remains have been recovered from a 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...

 or Paleogene

Paleogene

The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

 deposit in Central Asia

Central Asia

Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...

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The relationships of this form are unknown; it was initially placed in the Presbyornithidae

Presbyornithidae

Presbyornithidae were a family of waterbirds with an apparently global distribution that lived until the Earliest Oligocene, but are now extinct...

, which at that time were believed to be some sort of "transitional shorebird". Recognizing that the presbyornithids were actually a prehistoric lineage of fairly advanced waterfowl

Waterfowl

Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....

, Zhylgaia was assigned to the form taxon

Form taxon

Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...

 "Graculavidae", an assemblage of Late Cretaceous and Paleocene

Paleocene

The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...

 shorebirds which are not a natural clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 but merely an assemblage of outwardly similar birds. All that can be said about this taxon is that it was a modern bird, in all probability a neognathe

Neognathae

Neognaths are birds within the subclass Neornithes of the class Aves. The Neognathae include virtually all living birds; their sister taxon Palaeognathae contains the tinamous and the flightless ratites....

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