''Nasidytes'' is an extinct genus of loon (

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 (Europe, Asia and debatably Africa), though prehistor ...

) that lived during the early

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

in what is now Great Britain. It contains a single species, ''N. ypresianus''. ''Nasidytes'' is the earliest unambiguously identified loon in the fossil record.

Discovery and naming

The

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 ...

of ''Nasidytes ypresianus'', ''NMS.Z.2021.40.24'', was collected in 1992 by Michael Daniels, in

Walton-on-the-Naze Walton-on-the-Naze is a seaside town on the North Sea coast. It is part of the parish of Frinton and Walton, in the Tendring District, Tendring district in Essex, England. The town is located north of Clacton and south of the port of Harwich; ...

Essex Essex ( ) is a Ceremonial counties of England, ceremonial county in the East of England, and one of the home counties. It is bordered by Cambridgeshire and Suffolk to the north, the North Sea to the east, Kent across the Thames Estuary to the ...

, UK. It is from the Walton Member of the London Clay Formation. The holotype is a partial skeleton including 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 ...

and most major wing,

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 o ...

, and leg bones. NMS.Z.2021.40.25, a left

carpometacarpus The carpometacarpus is a bone found in the hands of birds. It results from the fusion of the carpal and metacarpal bone, and is essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally fla ...

collected in 1996 by Daniels, has also been referred to ''N. ypresianus''. In 2022,

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.Mayr, Gerald (2016). ...

and Andrew C Kitchener described ''Nasidytes ypresianus''. The generic name is derived from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''nasus'' ("nose", in reference to the

semantically Semantics is the study of linguistic meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction between sense and reference ...

related word "Naze" in the name of the type locality) and the Greek δύτες (''dytes''), meaning "diver". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

refers to the

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 ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

, when the holotype dates to.

Description

The skeleton displays marked differences from modern

loon Loons (North American English) or divers (British English, British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family (biolog ...

s, more closely resembling fellow fossil loons '' Colymbiculus'' and ''

Colymboides The genus ''Colymboides'' contains three species of early loon dating from the late Oligocene or early Miocene. They are considered to be the earliest known unambiguous gaviiform fossils. The genus is widely known from early Priabonian – about ...

''. The mandible of ''Nasidytes'' is more like that of

coot Coots are medium-sized water birds that are members of the rail family, Rallidae. They constitute the genus ''Fulica'', the name being the Latin term for "coot". Coots have predominantly black plumage, and—unlike many rails—they are usual ...

s in its proportions than that of modern loons, indicating ''Nasidytes'' had a proportionally shorter and wider beak than its living relatives. The single preserved thoracic vertebra exhibits hollow spaces called pleurocoels, which are present in many neornithine

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

representatives but not in modern loons. The carpometacarpus is long, more than half the length of the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

; a long carpometacarpus is a derived trait of gaviiforms. The pedal

phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...

, particularly those of the second toe, are elongated, as in modern loons and many other

water bird A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabi ...

s. One of the ungual phalanges is preserved and has a shape characteristic for many birds with webbed feet.

Classification

Phylogenetic analysis 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 data ...

found ''Nasidytes'' to be the most basal member of Gaviiformes.

Paleobiology

Because of its differently-shaped beak, ''Nasidytes'' probably wasn't a pursuit predator of fish like modern loons, which have long, narrow, dagger-like beaks. Instead, with its shorter, wider beak, ''Nasidytes'' likely fed mainly on marine

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s. Though ''Nasidytes'' was aquatic, it was less adapted for sustained foot-propelled diving than modern loons. According to Mayr and Kitchener, "''Nasidytes'' might have had a

- or

diving duck The diving ducks, commonly called pochards or scaups, are a category of duck which feed by diving beneath the surface of the water. They are part of Anatidae, the diverse and very large family that includes ducks, geese, and swans. The diving ...

-like ecology, performing short, foot-propelled dives in search for food."

Paleoenvironment

The sediments ''Nasidytes'' was found in represent a nearshore marine environment.

References