''Birgeria'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of carnivorous marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

from the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

period. ''Birgeria'' had a global distribution, with fossil known from

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

Spitsbergen Spitsbergen (; formerly known as West Spitsbergen; Norwegian language, Norwegian: ''Vest Spitsbergen'' or ''Vestspitsbergen'' , also sometimes spelled Spitzbergen) is the largest and the only permanently populated island of the Svalbard archipel ...

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Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

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Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

and

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. The oldest fossils are from Griesbachian aged beds of the Wordie Creek Formation of East

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

. ''Birgeria'' existed throughout the entire Triassic period, from the very beginning just after the Permian-Triassic mass extinction, up to the very end with its extinction during the Triassic-Jurassic mass extinction. The type species was first described as ''Saurichthys mougeoti''. Following a reinvestigation, Erik Stensiö concluded that this species cannot be ascribed to ''

Saurichthys ''Saurichthys'' (from , 'lizard' and 'fish') is an extinct genus of predatory Actinopterygii, ray-finned fish from the Triassic period (geology), Period. It is the type genus of the family (taxonomy), family Saurichthyidae (Changhsingian-Ju ...

''. 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 Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...

) in 1915.

Systematics

''Birgeria'' is the only genus of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Birgeriidae and order Birgeriformes. The genera '' Psilichthys'', '' Ohmdenia'' 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 of Birgeriidae in his 1949 monograph. Birgeriidae first appears in the Early Triassic ( Induan) of

and went extinct in the

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

. It was most speciose during the Early and Middle Triassic. In most cladistic analyses, ''Birgeria'' and the

Saurichthyiformes Saurichthyiformes is an extinct order (biology), order of Actinopterygii, ray-finned fish which existed in Asia, Africa, Australia (continent), Australia, Europe and North America, during the late Permian to early Middle Jurassic. Saurichthy ...

are recovered as each others' closest relatives. Together, they are also often recovered as stem chondrosteans, closely related to sturgeons and paddlefish ( Acipenseriformes), with their exact relationship to each other and to sturgeons/paddlefish varying depending on the study. However, other studies have suggested that they are not closely related to Acipenseriformes, and instead are part of the stem-group of

Actinopterygii Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class (biology), class of Osteichthyes, bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built ...

, and thus are not closely related to any living group of fish. 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. A jaw fragment from the

of California, described as ''Xenestes velox'' by

David Starr Jordan David Starr Jordan (January 19, 1851 – September 19, 1931) was the founding president of Stanford University, serving from 1891 to 1913. He was an ichthyologist during his research career. Prior to serving as president of Stanford Universi ...

, was tentatively synonymized with ''Birgeria''. With about eight valid species, ''Birgeria'' was much less speciose than ''Saurichthys''. The following species are known: * †''B. acuminata'' (Agassiz, 1843) - Middle Triassic (

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

) of India, Late Triassic ( Carnian to Rhaetian) of Europe (Belgium, France, Germany, the Netherlands, Poland, Slovakia, Switzerland, and the United Kingdom) * †''B. aldingeri'' Schwarz, 1970 - Early Triassic ( Olenekian) of Norway * †''B. americana'' Romano et al., 2017 - Olenekian of

, US * †''B.? costata'' (

Münster Münster (; ) is an independent city#Germany, independent city (''Kreisfreie Stadt'') in North Rhine-Westphalia, Germany. It is in the northern part of the state and is considered to be the cultural centre of the Westphalia region. It is also a ...

, 1839 ) - Middle Triassic (Anisian to Ladinian) of Germany * †''B. groenlandica'' Stensiö, 1932 - Earliest Triassic ( Induan) of Greenland * †''B. guizhouensis''? Liu et al, 2006 - Carnian of China * †''B. liui'' Jin, 2001 - Ladinian to Carnian of China * †''B. mougeoti'' (Agassiz, 1844) - Induan to Olenekian of France and

* †''B. nielseni'' Lehman, 1948 - Induan of

* †''B. stensioei'' Aldinger, 1931 - Anisian of Italy * †''B.? velox'' (

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

, 1907) - Carnian/Norian of California, US Fossils of indeterminate species are known from Canada (

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

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, and

Saudi Arabia Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in West Asia. Located in the centre of the Middle East, it covers the bulk of the Arabian Peninsula and has a land area of about , making it the List of Asian countries ...

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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

and the hind portion of the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

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

heterocercal Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

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 is large. The "parietals" (

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

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 mammals h ...

is unpaired. The

maxilla In vertebrates, the maxilla (: maxillae ) 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. The two maxil ...

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 Chimaera, 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 contain ...

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 core part of the endoskeleton made of the bones of the head and trunk of vertebrates. In the human skeleton, it consists of 80 bones and is composed of the skull (28 bones, including the cranium, mandible and the midd ...

consists of ossified neural and

haemal arches A haemal arch, also known as a chevron, is a bony arch on the ventral side of a tail vertebra of a vertebrate. The canal formed by the space between the arch and the vertebral body is the haemal canal. A spinous ventral process emerging from the ha ...

, 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 individual shops are all owned by individual franchisees. The chain has three ...

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 or superpredator, 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 hig ...

among Triassic

, together with ''

''. Most species of ''Birgeria'' grew over in length, some even up to or possibly more. Some of the largest species are the Early Triassic ''Birgeria aldingeri'' (Spitsbergen) and ''Birgeria americana'' (Nevada). They were the first large-bodied predators after the Permian-Triassic mass extinction. 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 In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

. 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. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

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

Systematics

Appearance

Ecology

See also

References

Further reading