Saurichthys Semicostatus

''Saurichthys'' (from el, σαῦρος , 'lizard' and el, ἰχθῦς 'fish') is an extinct genus of predatory ray-finned fish from the Triassic period. It type genus family Saurichthyidae (Changhsingian-Middle Jurassic), and the largest and longest lasting genus in the family. This family also includes the Permian ''Eosaurichthys'' (China) and the Jurassic ''Saurorhynchus'' (= ''Acidorhynchus'') from Europe and North America, though it may be more appropriate to treat these as subgenera of ''Saurichthys,'' due to the genus ''Saurichthys'' otherwise being paraphyletic.''''

Fossils of ''Saurichthys'' have been found on all continents except South America and Antarctica.''Saurichthys''
at Fossilworks.org It inhabited both marine and freshwater environments. The oldest fossils of ''Saurichthys'' were recovered from the Wordie Creek Formation in East Greenland and are Griesbachian (Induan, Early Triassic) in age.

Over 50 species of ''Saurichthys'' have been described (see list below). The species differ in size and show variability in their skeletal features. The latter can potentially be ascribed to changes in major developmental genes. The use of subgenera (''Eosaurichthys'', '' Costasaurichthys'', '' Lepidosaurichthys'', ''Saurorhynchus'', ''Sinosaurichthys'') in the literature reflects differences in morphology between species groups. Several species that were described predominantly in the 19th century are based on fragmentary fossils (often isolated teeth). These are mostly considered invalid species by modern taxonomic standards.

Louis Agassiz, who described the type species of ''Saurichthys'' in 1834, named it the "lizard fish" because of skeletal features that he thought were intermediate to reptiles and fishes.

Their exact phylogenetic position is uncertain, though it is agreed that they are not members of Neopterygii. Historically, they have been seen as close relatives of the Acipenseriformes (which includes living sturgeon and paddlefish), though this has been strongly questioned by modern studies.

Appearance

''Saurichthys'' was an elongate, streamlined fish, commonly about to long. Some species were only a few decimetres long (e.g. ''Saurichthys minimahleri''), while others could grow up to about in length (specimen from the Middle Triassic of Turkey).

Species of ''Saurichthys'' had an elongate bodyform superficially similar to the modern garfish. Its dorsal and anal fins were placed opposite each other well back on the body, and the tail was symmetrical (abbreviate diphycercal). These features would have made it a powerful swimmer, and it is presumed to have hunted in a similar way to the pike, attacking from an ambush at high speed. Its jaws were extremely long, making up a third of the total body length, and ended in a sharp, beak-like tip. Two to six longitudinal scale rows are developed, with small scales in between in some species.

The axial skeleton consists of ossified neural and haemal arches. Haemal arches may develop spines. The neural arches often show spines as well as other projections interpreted as prezygapophyses and postzygapophyses. Ossified centra are missing. The axial skeleton shows regionalization, meaning that there are differences in bone morphology between segments of the axial skeleton. Some species show dedifferentiation of the axial skeleton.

Ecology and Evolution

Large species of ''Saurichthys'' were apex predators among Triassic ray-finned fish, together with the marine ''Birgeria'' (Birgeriidae).

''Saurichthys'' is classically interpreted as an ambush predator. It first approached its prey and then attacked it by quick, sudden darts. Some species may have lived as subsurface cruisers (''Sinosaurichthys'').

Specimens showing half-swallowed conspecific individuals suggest that cannibalism was relatively common in ''Saurichthys''. Fossil evidence, in the form of a bolus (ball-shaped mass) of bones in the same strata, indicates that ''Saurichthys'' attacked marine reptiles such as the tanystropheid '' Langobardisaurus'', or possibly scavenged their corpses.

A study on the gastrointestinal tract of ''Saurichthys'' found similarities with present-day sharks and rays, in particular the many windings in the spiral valve. The many windings increased the surface area for digestion, which is sure to have provided the fish with more energy. It indicates that ''Saurichthys'' had an energy-laden lifestyle.

Early Triassic species of ''Saurichthys'' differ from later species most prominently in their more elongate postorbital portion of the skull (part of the skull behind the eyes) and their generally denser scale cover. Middle Triassic and Late Triassic species, on the other hand, typically have a short postorbital portion of the skull and their scale cover is reduced. This reduction includes both the number of the longitudinal scale rows and the size of individual scales. These evolutionary trends are, however, not an indication for anagenesis, but rather the result of parallel evolution in different lineages of ''Saurichthys''. The aforementioned trends are observed only in marine species. Late Triassic freshwater species of Saurichthys (e.g., ''S. orientalis'', ''S. sui'') retain an elongate postorbital skull portion and a denser scale cover, suggesting that freshwater environments served as refugia for species with a more primitive appearance.

Reproduction

Fossils of gravid females provide evidence for (ovo-)viviparity in ''Saurichthys'' and the oldest known example for viviparity in ray-finned fishes.

Internal fertilisation is also evidenced by specialized pelvic fin rays ('' Saurichthys calcaratus'') or ventral scales (gonopodium; ''Saurichthys curionii'', ''Saurichthys macrocephalus'') that are interpreted as copulatory organs of males.

Species

This list includes species of ''Saurichthys'' that are generally considered valid (based on Romano et al. and references cited below). The validity of species that are based on fragmentary material (e.g., isolated scales or teeth) is questionable (see below).

* †''Saurichthys'' ('' Costasaurichthys'' Tintori 2013)
** †''Saurichthys'' (''Costasaurichthys'') ''costasquamosus'' Rieppel 1985
** †''Saurichthys'' (''Costasaurichthys'') ''paucitrichus'' Rieppel 1992
* †''Saurichthys'' (''Eosaurichthys'' Liu and Wei 1988)
** †''Saurichthys'' (''Eosaurichthys'') ''chaoi'' (Liu and Wei 1988)
** †''Saurichthys'' (''Eosaurichthys'') ''madagascariensis'' Piveteau 1945
* †''Saurichthys'' ('' Lepidosaurichthys'' Tintori 2013)
** †''Saurichthys'' (''Lepidosaurichthys'') ''dayi'' (Raymond 1925)
** †''Saurichthys'' (''Lepidosaurichthys'') ''elongatus'' Stensiö 1925
** †''Saurichthys'' (''Lepidosaurichthys'') ''ornatus'' Stensiö 1925
** †''Saurichthys'' (''Lepidosaurichthys'') ''toxolepis'' Mutter et al. 2008
** †''Saurichthys'' (''Lepidosaurichthys'') ''wimani'' (Woodward 1912)
* †''Saurichthys'' (''Saurorhynchus'' Agassiz 1844)
** †''Saurichthys'' (''Saurorhynchus'') ''calcaratus'' Griffith 1977
** †''Saurichthys'' (''Saurorhynchus'') ''deperditus'' (Costa 1862)
** †''Saurichthys'' (''Saurorhynchus'') ''striolatus'' Bronn 1858
** †''Saurorhynchus acutus'' (Agassiz 1844)
** †''Saurorhynchus anningae'' Maxwell & Stumpf 2017
** †''Saurorhynchus brevirostris'' (Woodward 1895)
** †''Saurorhynchus hauffi'' Maxwell & Stumpf 2017
* †''Saurichthys'' (''Sinosaurichthys'' Wu et al. 2011)
** †''Saurichthys'' (''Sinosaurichthys'') ''longipectoralis'' Wu et al. 2011
** †''Saurichthys'' (''Sinosaurichthys'') ''longimedialis'' Wu et al. 2011
** †''Saurichthys'' (''Sinosaurichthys'') ''minuta'' Wu et al. 2011
* †''Saurichthys apicalis'' Agassiz 1834 (type species)
* †'' Saurichthys breviabdominalis'' Maxwell et al. 2015Discovery of two new species of primitive fishes
/ref>
* †''Saurichthys curionii'' (Bellotti 1857)
* †'' Saurichthys daubreei'' Firtion 1934
* †''Saurichthys dawaziensis'' Wu et al. 2009
* †'' Saurichthys dianneae'' Maxwell et al. 2016
* †'' Saurichthys dongusensis'' Minich 1992
* †'' Saurichthys eximius'' Minikh 1982
* †''Saurichthys gigas'' (Woodward 1890), non-von Quenstedt 1858
* †'' Saurichthys gracilis'' (Woodward 1890)
* †'' Saurichthys grignae'' Tintori 2013
* †'' Saurichthys gypsophilus'' Reis 1892
* †'' Saurichthys hamiltoni'' Stensiö 1925
* †'' Saurichthys hoffmanni'' Werneburg et al. 2014
* †'' Saurichthys huanshenensis'' Chou & Liu 1957
* †'' Saurichthys irregularis'' Oertle 1928
* †'' Saurichthys latifrons'' Eck 1865
* †''Saurichthys lepidosteoides'' Frech 1903
* †'' Saurichthys macrocephalus'' (Deecke 1889)
* †'' Saurichthys majiashanensis'' Tintori et al. 2014
* †'' Saurichthys minimahleri'' Werneburg et al. 2014
* †'' Saurichthys nepalensis'' Beltan & Janvier 1978
* †''Saurichthys obrutchevi'' Minich 1981
* †''Saurichthys orientalis'' Sytchevskaya 1999
* †'' Saurichthys parvidens'' Wade 1935
* †'' Saurichthys piveteaui'' Beltan 1968
* †'' Saurichthys proximus'' Minich 1981
* †'' Saurichthys rieppeli'' Maxwell et al. 2015
* †'' Saurichthys sceltrichensis'' Renesto et al. 2021
* †'' Saurichthys seefeldensis'' Kner 1867
* †'' Saurichthys spinosa'' Wu et al. 2018
* †'' Saurichthys stensioi'' Lehman 1952
* †'' Saurichthys sui'' Fang & Wu 2022
* †''Saurichthys tenuirostris'' Münster 1839Fossilworks: ''Saurichthys'' Agassiz 1843
/ref>
* †'' Saurichthys tertius'' Minich 1982
* †'' Saurichthys ultimus'' Minikh 1992
* †'' Saurichthys vjuschkovi'' Minikh 1983
* †'' Saurichthys yangjuanensis'' Wu et al. 2015
* †'' Saurichthys yunnanensis'' Zhang, Zhou, Lu & Bai 2010

Species based on fragmentary fossils

* †'' Saurichthys aculeatus'' Henry 1876
* †'' Saurichthys annulatus'' Winkler 1880
* †'' Saurichthys catalaunicus'' (Betlan 1972)
* †''Saurichthys indicus'' de Koninck 1863
* †'' Saurichthys listroconus'' Plieninger 1844
* †'' Saurichthys longiconus'' Agassiz 1834
* †'' Saurichthys longidens'' Agassiz 1844
* †'' Saurichthys osseus'' (Betlan 1972)
* †'' Saurichthys semicostatus'' Münster 1839
* †'' Saurichthys striatulus'' Henry 1876
* †'' Saurichthys subulatus'' Henry 1876

Synonyms

* †'' Saurichthys acuminatus'' Agassiz 1844 → †''Birgeria acuminata''
* †''Saurichthys acutus'' Agassiz 1844 → †''Saurorhynchus acutus''
* †'' Saurichthys brevirostris'' (Woodward 1895) → †''Saurorhynchus brevirostris''
* †'' Saurichthys costatus'' Münster 1839 → †''Birgeria? costata''
* †''Saurichthys elegans'' Stensiö 1925 → †''Saurichthys elongatus''
* †''Saurichthys intermedius'' (Bassani 1886) → †''Saurichthys curionii''
* †'' Saurichthys krambergeri'' Schlosser 1918 → †'' Saurichthys deperditus''
* †'' Saurichthys mougeoti'' Agassiz 1844 → †''Birgeria mougeoti''
* †'' Saurichthys robustus'' Bassani 1886 → †''Saurichthys curionii'', †'' Saurichthys macrocephalus'', †''Saurichthys costasquamosus''
* †'' Saurichthys stoppanii'' (Bassani 1886) → †''Saurichthys curionii''

References

External links

Saurichthys species information
on paleodb.org.

{{Taxonbar, from=Q2267091

Saurichthyiformes
Triassic bony fish
Prehistoric ray-finned fish genera
Prehistoric fish of Africa
Triassic fish of Asia
Prehistoric fish of Australia
Triassic fish of Europe
Fossil taxa described in 1834
Taxa named by Louis Agassiz