''Birgeria'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of carnivorous marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

from the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. ''Birgeria'' had a global distribution. Fossils were found in

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

, Spitsbergen,

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, Switzerland,

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

Slovenia Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...

, China,

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Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

and

Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

. The oldest fossils are from

Griesbachian The Induan is the first age of the Early Triassic epoch in the geologic timescale, or the lowest stage of the Lower Triassic series in chronostratigraphy. It spans the time between 251.902 Ma and Ma (million years ago). The Induan is sometime ...

aged beds of the Wordie Creek Formation of East

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...

. The type species was first described as ''Saurichthys mougeoti''. Following a reinvestigation,

Erik Stensiö Prof Erik Helge Osvald Stensiö HFRSE (2 October 1891 – 11 January 1984) was a Swedish paleozoologist. He later took his new surname from his place of origin and is occasionally referred to with both names (as Erik Andersson Stensiö, Erik ...

concluded that this species cannot be ascribed to '' Saurichthys''. He thus erected a new genus, which he named after his colleague Birger Sjöström, who had joined him on an expedition to the Arctic island of Spitsbergen ( Svalbard) in 1915.

Appearance

The scale cover of ''Birgeria'' is reduced. Most of the body is devoid of scales. Scales are only developed on the upper lobe of the

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

and the hind portion of the

caudal peduncle Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

. The scales are small, rhombic and lack a ganoine layer. The

heterocercal Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

tail fin is large and deeply forked. The dorsal and anal fins are situated at the same level in the back of the body. The fin rays are segmented. Birgeria stensioei skeleton

The eyes were located in the front of the skull. The jaws are long and the

gape The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food ...

is large. The "parietals" (

postparietal Postparietals are cranial bones present in fish and many tetrapods. Although initially a pair of bones, many lineages possess postparietals which were fused into a single bone. The postparietals were dermal bones situated along the midline of the ...

s) are small and medially separated by the elongate "frontals" ( parietals). The postrostral is large. The (rostro-)

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

is unpaired. The

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

is cleaver-shaped with a large postorbital blade. Two to three rows of conical teeth are present. The teeth normally show cutting edges. The preopercle is boomerang-shaped. The bones of the

gill cover The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

are small, often weakly

ossified Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

or not ossified at all. The

axial skeleton The axial skeleton is the part of the skeleton that consists of the bones of the head and trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts; the skull (22 bones), also the ossicles of the middle ...

consists of ossified neural and haemal arches, both of which may show spines, and additional supraneurals. Other elements are interpreted as parapophyses. Ossified

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different ...

are missing. The axial skeleton is regionalized, meaning that there are differences in bone

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

between segments of the axial skeleton, although these differences are relatively subtle in ''Birgeria''.

Ecology

Triassic marine vertebrate apex predators

''Birgeria'' was an

apex predator An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...

among Triassic

, together with '' Saurichthys''. Most species of ''Birgeria'' grew over in length, some even up to or possibly more. Some of the largest species are the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

''Birgeria aldingeri'' (Spitsbergen) and ''Birgeria americana'' (Nevada). A specimen of ''Birgeria nielseni'' from Madagascar was described as supposedly carrying embryos whose bodies are covered with rhombic scales. However, this interpretation was later dismissed. It is more likely that these "embryos" were actually preyed ray-fins, which would indicate that the diet of ''Birgeria'' included small actinopterygians. Unlike ''Saurichthys'', ''Birgeria'' was probably not

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

. This view is supported by the fact that fossils with copulatory organs are yet unknown. Based on its anatomical features, ''Birgeria'' is interpreted as a

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

, swift swimmer. Fossils are sparse, which supports the view that it lived offshore.

Systematics

''Birgeria'' is the only genus of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Birgeriidae (

monotypy In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

). The genera ''

Psilichthys ''Psilichthys'' is an extinct genus of prehistoric bony fish from Eumeralla Formation, the Lower Cretaceous epoch of what is now Victoria, Australia, known from single species ''P. selwyni''. This is the first Mesozoic fossil vertebrate named ...

'', ''

Ohmdenia ''Ohmdenia'' is an extinct genus of prehistoric bony fish that lived from the Toarcian stage of the Early Jurassic epoch. ''Ohmdenia'' was first described in 1953 by B. Hauff, based on a fossil found in the well-known Posidonia Shale in Holzma ...

'' and '' Brazilichthys'' have been previously referred to Birgeriidae, but they were shown to be only distantly related to ''Birgeria''. The family was erected by Hermann Aldinger in 1937. Eigil Nielsen gave the first

diagnosis Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems engin ...

of Birgeriidae in his 1949 monograph. Birgeriidae first appears in the

(

Induan The Induan is the first age of the Early Triassic epoch in the geologic timescale, or the lowest stage of the Lower Triassic series in chronostratigraphy. It spans the time between 251.902 Ma and Ma (million years ago). The Induan is sometime ...

) of

and went extinct in the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

. It was most speciose during the Early and

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

. Birgeriidae is the only family of Birgeriformes Heyler, 1969 (

).Romano, C. & Brinkmann, W. (2009). "Reappraisal of the lower actinopterygian ''Birgeria stensioei'' ALDINGER, 1931 (Osteichthyes; Birgeriidae) from the Middle Triassic of Monte San Giorgio (Switzerland) and Besano (Italy)". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 252: 17–31. doi:10.1127/0077-7749/2009/0252-0017. In cladistic analyses, ''Birgeria'' and ''Saurichthys'' are often recovered as stem

chondrosteans Chondrostei is a group of non-neopterygian ray-finned fish, while the term originally referred to a paraphyletic group of all non-neopterygian ray-finned fish, it was redefined by Patterson in 1982 to be a clade comprising the Acipenseriformes (w ...

, closely related with sturgeons and their relatives. A few species, such as ''Birgeria''? ''costata'' or ''Birgeria''? ''annulata'', are only known from fragmentary material. Their affinity with ''Birgeria'' is uncertain. The type material of ''Birgeria guizhouensis'' appears to be lost. With about eight valid species, ''Birgeria'' was much less speciose than ''Saurichthys''.

Appearance

Ecology

Systematics

References

Further reading