''Ypresiglaux'' (meaning "

Ypresian 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 ...

owl") is an extinct genus of

strigiform 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 ...

bird from the

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

London Clay Formation of

Essex Essex () is a county in the East of England. One of the home counties, it borders Suffolk and Cambridgeshire to the north, the North Sea to the east, Hertfordshire to the west, Kent across the estuary of the River Thames to the south, and G ...

, United Kingdom and

Nanjemoy Formation The Nanjemoy Formation is a geologic formation pertaining to both the Wilcox Group and the Pamunkey Group of the eastern United States, stretching across the states of Virginia, Maryland, and District of Columbia. The formation crops out east of ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

, United States. The genus contains two species: ''Y. michaeldanielsi'', known from a partial skeleton, and ''Y. gulottai'', known from a distal tarsometatarsus.

Discovery and naming

''Ypresiglaux'' was described in 2022 by German paleontologist

Gerald Mayr Gerald Mayr is a German palaeontologist who is Curator of Ornithology at the Senckenberg Research Institute in Frankfurt am Main, Hesse. He has published extensively on fossil birds, especially the Paleogene avifauna of Europe. He is an expert on ...

and British zoologist Andrew C. Kitchener. The generic name, "''Ypresiglaux''", combines a reference to the

-dated type locality with the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word "glaux," meaning "owl". The type species, ''Y. michaeldanielsi'', was described on the basis of a partial skeleton collected in 1992. This specimen, NMS.Z.2021.40.26, which includes the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of t ...

, wing bones, and a partial right leg, was designated as the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

. NMS.Z.2021.40.27, an additional specimen collected in 1982, consists of the distal portion of the right

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

, distal half of the right

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 bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) and meta ...

, and pedal

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

. It was also referred to ''Y. michaeldanielsi''. These fossils were discovered by Michael Daniels in layers of the London Clay Formation (Walton Member), dated to the early

, which is located near

Walton-on-the-Naze Walton-on-the-Naze is a seaside town on the North Sea coast and (as Walton le Soken) a former civil parish, now in the parish of Frinton and Walton, in the Tendring district in Essex, England. It is north of Clacton and south of the port of Ha ...

in Essex, England. The specific name, "''michaeldanielsi''", honors Michael Daniels. ''Y. michaeldanielsi'' represents one of the most completely-known

Palaeogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...

owls. Additional fossil material, consisting of a partial right femur, partial right tarsometatarsus, and pedal phalanges (specimen NMS.Z.2021.40.27) was also collected from the Walton Member of the London Clay Formation. Since the fossil material is slightly larger than overlapping bones of ''Y. michaeldanielsi'', it is possible that it represents a female specimen of the latter, since

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

has been consistently observed in owls. Some important differences between the bones suggest that they may represent a distinct species. However, due to the lack of morphological differences, the specimen could not be confidently placed beyond "''Ypresiglaux'' sp." In 2016, Gerald Mayr described a distal right tarsometatarsus as belonging to a new species of the extinct owl genus ''

Eostrix ''Eostrix'' is a genus of extinct primitive owls in the family Protostrigidae, along with ''Oligostrix'' and ''Minerva''. These owls date from the early Eocene of the United States, Europe, and Mongolia. They have been described based on fossil ...

'', ''E. gulottai''. The holotype specimen, SMF Av 627, was discovered in layers of the Eocene (Ypresian)-dated

(Potapaco Member) of Stafford County, Virginia, USA. In 2022, Mayr and Kitchener moved '' 'Eostrix' gulottai'' to the new genus ''Ypresiglaux'' as the new combination, ''Y. gulottai''. The specific name honors Marco Gulotta, the discoverer of the specimen.

Description

''Ypresiglaux'' was a very small owl. ''Y. michaeldanielsi'' was comparable in size to the Eurasian Pygmy Owl, which has a body mass of 50–77 grams. ''Y. gulottai'' was even smaller, and represents the smallest known owl (extinct or extant). It is suggested that it likely had a diet comparable to the similarly-sized extant

long-whiskered owlet The long-whiskered owlet (''Xenoglaux loweryi'') is a tiny owl that is endemic to a small area in the Andean mountains in Amazonas and San Martín in northern Peru. It is restricted to cloud forests with dense undergrowth and epiphytes at about ...

and

elf owl The elf owl (''Micrathene whitneyi'') is a small grayish-brown owl about the size of a sparrow found in the Southwestern United States, central Mexico, and the Baja California peninsula. It has pale yellow eyes highlighted by thin white "eyebrow ...

, which primarily eat

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

. It is likely that ''Ypresiglaux'' did not have the same degree of head rotational mobility as extant owls because of differences in the

atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...

and

axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...

. Mayr and Kitchener (2022) further suggest that ''Ypresiglaux'' occupied a diurnal niche, contrary to extant owls, which are often

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

. Preserved fossilized toe pad

integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind. Etymology The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...

was observed on a piece of

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

collected with a pedal phalanx. A similar instance was seen in the holotype of the contemporary ''

Lutavis ''Lutavis'' (meaning "clay bird") is an extinct genus of potentially afroavian bird from the Early Eocene London Clay Formation of Essex, United Kingdom. The genus contains a single species, ''L. platypelvis'', known from a partial skeleton. ...

''.

Classification

In their

phylogenetic analyses In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

, Mayr & Kitchener (2022) recovered ''Ypresiglaux'' in various positions within the Strigiformes. They stated that the discovery of additional fossil material could provide more insight into the exact phylogenetic relationships of ''Ypresiglaux''. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

below displays the results of two different phylogenetic analyses. Topology 1: Strict consensus tree Topology 2: 50% majority-rule consensus tree

References

{{Taxonbar, from1=Q113656843, from2=Q113784812, from3=Q113799510 Owls Eocene birds of North America Extinct birds of North America Eocene birds of Europe Extinct birds of Europe Prehistoric bird genera Birds described in 2022 Fossil taxa described in 2022

Discovery and naming

Description

Classification

See also

References