''Oreochima'' is an archaeomaenid

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

Lower Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic–Jurassic extinction event, 201.3 Ma&nb ...

-aged freshwater strata of

Queen Alexandra Range The Queen Alexandra Range () is a major mountain range about long, bordering the entire western side of Beardmore Glacier from the Polar Plateau to the Ross Ice Shelf. The range is in the Transantarctic Mountains System, and is located in the Ross ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

. Fossils come from the Lower Jurassic

Mawson Formation The Mawson Formation is a geological formation in Antarctica, dating to roughly between 182 and 177 mya (unit), million years ago and covering the Toarcian faunal stage, stages of the Jurassic Period in the Mesozoic Era. Vertebrate remains are kn ...

(

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

) of Storm Peak, Antarctica, where a freshwater lake system, called "Lake Carapace", once existed. ''O. ellioti'' is also notable for being one of few archaeomaenid genera found outside of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, as well for be one of the oldest members of the family.

Description

Two nearly complete specimens of ''Oreochima ellioti'' (specimens AMNH 9910 and AMNH 9916) have an average total length of about 60 mm, with incomplete specimens representing individuals of similar size. The frontals taper anteriorly and were slightly notched where they were in contact with the nasals. The opercular bone was about twice as high as the subopercular.

Phylogeny

The

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

below is simplified after a

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 ...

by Bean (2021). Archaeomaenidae was recovered as one of the most basal stem-teleost clades, lying crownward of the families Pachycormidae and

Aspidorhynchidae Aspidorhynchidae (from Neo-Latin "shield-snouts") is an extinct family of ray-finned fish from the Mesozoic Era. It is the only member of the monotypic order Aspidorhynchiformes. Members of the group are noted for their elongated, conical rostrum ...

, but stemward of the family Pholidophoridae:

Paleoenvironment

The

represents the fossiliferous interbeds of the Kirkpatrick Basalt, part of the Ferrar Group volcanic events, with age constraint in between 180+/-3.5 Ma-176.6+/-1.8 Ma, well correlated with the evolution of the Ferrar Large Igneous Province during the initial breakup of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. This layers record sedimentary and biotic processes in relatively shallow lakes and ponds, and in surrounding wetlands to upland areas, with the biota of the lakes having access to magmatic sources. The so called "Lake Carapace", the main water body recovered locally, was, like the "Chacritas Paleolake" of the sister

Cañadón Asfalto Formation The Cañadón Asfalto Formation is a geological formation from the Lower Jurassic, with doubtful layers of Late Jurassic age previously referred to it. The Cañadón Asfalto Formation is located in the Cañadón Asfalto Basin, a rift basin in th ...

in Patagonia, developed following the local rift in a similar way to the modern

Lake Magadi Lake Magadi is the southernmost lake in the Kenyan Rift Valley, lying in a catchment of faulted volcanic rocks, north of Tanzania's Lake Natron. During the dry season, it is 80% covered by soda and is known for its wading birds, including f ...

in the

Kenyan Rift Valley The Great Rift Valley is part of an intra-continental ridge system that runs through Kenya from north to south. It is part of the Gregory Rift, the eastern branch of the East African Rift, which starts in Tanzania to the south and continues no ...

, as proven by the discovery of

Chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

like the one found in this African lake, that suggests both, Carapace and Chacritas were likely alkaline lakes that had inflows of hydrothermal fluids.

Hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

activity help the development of microbes (

Archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

) and helping the fauna on cooler events. Alongside ''Oreochima'' lived the

spinicaudata Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classif ...

n '' Carapacestheria disgregaris'',

notostraca The order Notostraca, containing the single family Triopsidae, is a group of crustaceans known as tadpole shrimp or shield shrimp. The two genera, ''Triops'' and ''Lepidurus'', are considered living fossils, with similar forms having existed since ...

n branchiopods,

ostracoda Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant) have been identified,Brandão, S.N.; Antonietto, L.S; Nery, D.G.; Santos, S.G.; Karano ...

, up to 50 specimens of

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

nymphs and wings (

mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...

, the

dragonfly A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threat ...

Caraphlebia ''Caraphlebia'' is an extinct genus of Dragonfly, dragonflies, known from the Early Jurassic Mawson Formation of Antarctica. It is one of the only named fossil insects from Antarctica that have been formally described; others include two beetles ...

antartica'', and a

Coleoptera Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...

n). and plant leaves ('' Zamites'').

References

External links

* Archaeomaenidae Early Jurassic fish Fossil taxa described in 1972 Fossils of Antarctica Prehistoric fish of Antarctica {{jurassic-fish-stub

Description

Phylogeny

Paleoenvironment

See also

References

External links