Halcyornithidae is an extinct family of telluravian birds thought to be related to the Psittaciformes (parrots),

Passeriformes A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped') which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their ...

(songbirds), and to the extinct Messelasturidae. Halcyornithids have been found in various Eocene formations in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

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 ...

. Widespread and diverse in the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

of North America and Europe, halcyornithids are not found in locales later than the

Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...

. Halcyornithids were small, arboreal birds with zygodactyl feet, with two toes facing forwards and two facing back, a trait shared with other tree-dwelling families of Eocene birds like the Zygodactylidae and the messelasturids. The skull of halcyornithids features a ridge of bone above the eye called the supraorbital process, similar to birds of prey. The relationships of the halcyornithids to other birds remain uncertain. Halcyornithids have been proposed as relatives to

owl Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...

s and as a lineage closer to parrots than to songbirds. Most recently, halcyornithids have been identified as the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

including parrots and songbirds. It is also possible that Halcyornithidae is

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

with respect to the Messelasturidae.

Description

Halcyornithids are recognisable by details of the skull and limbs. The

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) a ...

, the lowermost bone of the leg, is short and shaped like those of parrots. The distal end of the tarsometatarsus has a projection of bone that supports the fourth toe, which is reversed and faces backwards. Unlike in parrots, however, this projection is not separated by a groove from the rest of the trochlea supporting the other toes. The third toe is strongly built, more so than the others. The humerus is long and slender, and the

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

is shaped like that found in owls, and has a

foramen In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, artery, ...

for the supracoracoideus nerve. The skulls of halcyornithids bear a prominent shelf of bone above the upper margin of the eye, the supraorbital process, comparable to that present in falcons and other birds of prey. One proposed function of the supraorbital process is mechanical protection of the eyeball from injury, for example, such as might be caused by struggling prey animals being killed with the beak. The morphology of the head is overall similar to that of messelasturids, but in halcyornithids, the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

is proportionally much longer.

Distribution

A high diversity of halcyornithid birds is found in the Eocene

London Clay The London Clay Formation is a Sediment#Shores and shallow seas, marine formation (geology), geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) age which outcrop, crops out in the southeast of England. The London C ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

, from sites near Walton-on-the-Naze and the

Isle of Sheppey The Isle of Sheppey is an island off the northern coast of Kent, England, neighbouring the Thames Estuary, centred from central London. It has an area of . The island forms part of the districts of England, local government district of Borough ...

. Of the specimens collected from that location, almost none do not bear minor morphological dissimilarities to others, indicating that there were likely many species living in the area, comprising an

adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...

. Halcyornithids are also known from the

Messel Pit The Messel Formation is a Formation (geology), geologic formation in Hesse, central Germany, dating back to the Eocene Epoch (geology), epoch (about 47 Ma). Its geographic range is restricted to the Messel pit. There it unconformably overlie ...

, in

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, where specimens likewise exhibit diversity. Other halcyornithid-bearing sites in Europe include the Geisel Valley of Germany, which has produced the most recent evidence of halcyornithids, of

age, the Fur Formation in

Denmark Denmark is a Nordic countries, Nordic country in Northern Europe. It is the metropole and most populous constituent of the Kingdom of Denmark,, . also known as the Danish Realm, a constitutionally unitary state that includes the Autonomous a ...

, and the Egem in

Belgium Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. Situated in a coastal lowland region known as the Low Countries, it is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeas ...

. From the

Menat In ancient Egyptian religion, a menat (, ) was a necklace closely associated with the goddess Hathor. Operation The menat was held in the hand by its counterpoise and used as a Rattle (percussion instrument), rattle by Hathor's priestesses. It ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

is a skeleton tentatively believed to be a halcyornithid, which may also be of

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

age. In the

, halcyornithids have been found in the

Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River (Colorado River), Green River in Colorado, Wyoming, and Utah. The sedimen ...

of the US state of

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

as well as the Nanjemoy Formation of the state of

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

Classification

Placement of the Halcyornithidae after Ksepka et. al, 2019. Internal classification of the Halcyornithidae and Messelasturidae after Mayr & Kitchener, 2022.

References

{{Taxonbar, from=Q49001519 Eocene birds Prehistoric birds of Europe Prehistoric birds of North America Prehistoric bird families