Santanichthys

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Santanichthys
Temporal range: Early Cretaceous, 125–112  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Genus: Santanichthys
Silva Santos, 1991
Species:
S. diasii
Binomial name
Santanichthys diasii
(Silva Santos, 1958)

Santanichthys diasii is a species of extinct fish that existed around 115 million years ago during the Albian age. S. diasii is regarded as the basal-most characiform, and is the earliest known member of Otophysi. [1] It appears as a small fish, similar in appearance to a modern-day herring little more than 30 millimeters in length. Its most striking characteristic is the presence of a Weberian apparatus, which makes it the most primitive known member of the order Characiformes, [1] the order in which modern-day tetras [2] (including piranhas [3] [4] ) are classified. Santanichthys has been unearthed from numerous locations throughout Brazil, in rocks dating to the Cretaceous Period. Its presence in these strata is seen as an indicator for the biogeography and evolution of its order.

Anatomy and morphology

Santanichthys is a small, characiform fish that would have superficially resembled more advanced tetras or the unrelated herrings. Maximum length appears to be around 3-4 centimeters standard length. The species possesses a primitive but complete Weberian Apparatus, formed from the first four vertebrae of the spinal column. This is the earliest occurrence of the structure found in any known taxon of fish. Anatomically, the fish is similar to many others within its order. The body is semi-laterally compressed and ovate. The fins are more or less complete for a characiform - Santanichthys possesses a single dorsal, anal and caudal fin and paired pectoral and pelvic fins. Skeletal-wise, the fish has from 30-40 elongated vertebrae. A complex suspensorium can be found in the taxon. Jaw teeth however, are noticeably absent. Cycloid scales are wholly present throughout the entire body. [1]

Range and distribution

Fossils of Santanichthys were first unearthed from the Romualdo Member of the Santana Formation in northeastern Brazil. The formation, situated in the hills of the Araripe Basin, is highly renowned for its rich Early Cretaceous fauna. The specific rock strata where fossils of Santanichthys were gathered from date back to the Aptian stage of the Cretaceous period. A large part of this faunal assemblage are masses of fossilized fish found at semi-regular intervals, including shoals of Santanichthys in various states of preservation. [5] Aside from the Santana, Santanichthys fossils have also been found in other Cretaceous deposits in Brazil. The Cretaceous deposits of the Brazilian Riachuelo Formation, specifically the Taquari Member have yielded specimens of Santanichthys. Fossils of the taxon have also been unearthed from the Codo Formation in the Parnaiba Basin of Northeastern Brazil. [1]

The type specimen, DGM-DNPM 647P was taken from Albian deposits of the Romualdo Member in the Santana Formation. It is a fossil of a complete fish, around 4 centimeters long from snout to the base of the tail. At least two dozen specimens are kept by the American Museum of Natural History as AMNH 20050-20075. Some specimens of Santanichthys were taken from the fossilized stomach contents of other, larger fish such as AMNH 19439 and AMNH 12826. [1]

Evolutionary history

Santanichthys diasii is the only species within the genus Santanichthys. It is classified in the order Characiformes, an order that includes the tetras. Analysis of its morphological characters, including the presence of enlarged lagenar capsules has placed it as one of the most basal characiforms. This, combined with the Early Cretaceous origin of these specimens, makes Santanichthys the earliest known otophysan; [1] The next characiforms up the fossil record date from the Late Cretaceous period already. This has several implications on the evolution of the Characiformes. All modern characiforms are strictly freshwater species. The Santana Formation is a marine sedimentary formation and thus Santanichthys was most likely an inhabitant of brackish or marine waters. This supports a marine-to-freshwater model of the evolution and dispersal of characiform species from the breakup of the continent Gondwana (Africa and South America) to the present day. [6]

Taxonomic history

Santanichthys diasii was first described within the genus Leptolepis as Leptolepis diasii in 1958. The specimens, fossilized fish from the Santana Formation no more than thirty centimeters long apiece, were simply described as "prehistoric teleosts" and not much anatomical comparison was done between the specimens and other previously-known prehistoric fish. [7] The second Leptolepis species described at the time of discovery, L. diasii found itself orphaned when the type species for the genus, L. bahiaensis was re-examined and reclassified in a different genus. L. diasii was deemed to be too different and anatomically advanced than others in the genus, and was rotated out of the genus in a 1991 classification by Maisey. [8] The species' current genus, Santanichthys was coined in the same year when the species was redescribed by its original describer. Because of several perceived anatomical structures, it was reclassified within the Clupeomorpha. [9] [10] Subsequent analyses of available Santanichthys fossil material have determined some structures to be akin to a primitive Weberian Apparatus, prompting reclassification of the taxon as a basal otophysan and within the Characiformes. [1]

Related Research Articles

<span class="mw-page-title-main">Characiformes</span> Order of fishes

Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.

<span class="mw-page-title-main">Crato Formation</span> Geologic formation of Early Cretaceous age in northeastern Brazil

The Crato Formation is a geologic formation of Early Cretaceous (Aptian) age in northeastern Brazil's Araripe Basin. It is an important Lagerstätte for palaeontologists. The strata were laid down mostly during the Aptian age, about 113 million years ago. It thought to have been deposited in a semi-arid lacustrine wetland environment.

<span class="mw-page-title-main">Anostomidae</span> Family of fishes

The Anostomidae are a family of ray-finned fishes that belong to the order Characiformes. Closely related to the Chilodontidae and formerly included with them, the Anostomidae contain about 150 described species. Commonly known as anostomids, they are found in freshwater habitats from the Río Atrato in northernmost South America to warm-temperate central Argentina; they are of Amazon origin, with few found west of the Andes. Their scientific name approximately means "mouth on top", from Ancient Greek áno- (ἄνω) "up" + stóma (στόμᾶ) "mouth", in reference to the arrangement of these fishes' mouth opening.

<span class="mw-page-title-main">Romualdo Formation</span> Brazilian geologic formation

The Romualdo Formation is a geologic Konservat-Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, previously designated as the Romualdo Member of the Santana Formation, named after the village of Santana do Cariri, lies at the base of the Araripe Plateau. It was discovered by Johann Baptist von Spix in 1819. The strata were deposited during the Aptian stage of the Early Cretaceous in a lacustrine rift basin with shallow marine incursions of the proto-Atlantic. At that time, the South Atlantic was opening up in a long narrow shallow sea.

<span class="mw-page-title-main">Weberian apparatus</span> Anatomical structure that connects the swim bladder to the auditory system in fishes

The Weberian apparatus is an anatomical structure that connects the swim bladder to the auditory system in fishes belonging to the superorder Ostariophysi. When it is fully developed in adult fish, the elements of the apparatus are sometimes collectively referred to as the Weberian ossicles or Weber's ossicles. The presence of the structure is one of the most important and phylogenetically significant distinguishing characteristics of the Ostariophysi. The structure itself consists of a set of minute bones that originate from the first few vertebrae to develop in an embryonic ostariophysan. These bones grow to physically connect the auditory system, specifically the inner ear, to the swim bladder. The structure acts as an amplifier of sound waves that would otherwise be only slightly perceivable by the inner ear structure alone.

<i>Tropeognathus</i> Genus of anhanguerid pterosaur from the Early Cretaceous

Tropeognathus is a genus of large pterosaurs from the late Early Cretaceous of South America. This genus is considered to be a member of the family Anhangueridae, however, several studies have also recovered it within another family called Ornithocheiridae. Both of these families are diverse groups of pterosaurs known for their keel-tipped snouts and large size. Tropeognathus is regarded as the largest pterosaur found in the Southern Hemisphere, only rivaled by the huge azhdarchids. The type and only species is Tropeognathus mesembrinus. Fossil remains of Tropeognathus have been recovered from the Romualdo Formation, which is a Lagerstätte located in the Santana Group of the Araripe Basin in northeastern Brazil.

<i>Leptolepis</i> Extinct genus of ray-finned fishes

Leptolepis is an extinct genus of stem-teleost fish that lived in what is now Europe during the Jurassic period.

Anhanguera is a genus of pterodactyloid pterosaur known from the Early Cretaceous Romualdo Formation of Brazil and the Late Cretaceous Kem Kem Group of Morocco. This pterosaur is closely related to Ornithocheirus, but belongs in the family Anhangueridae. The generic name comes from the Tupi words añanga, meaning "spirit protector of the animals" + wera "bygone".

Araripesaurus is a genus a pterosaur belonging to the suborder Pterodactyloidea, it was discovered in the Romualdo Formation of the Santana Group in northeastern Brazil, which dates back to the Aptian and Albian of the Early Cretaceous. The type species is A. castilhoi.

Brasileodactylus a genus of pterosaur from the Aptian-age lower Santana formation of Chapada do Araripe, Ceará, Brazil.

<i>Axelrodichthys</i> Extinct genus of coelacanths

Axelrodichthys is an extinct genus of mawsoniid coelacanth from the Cretaceous of Africa, North and South America, and Europe. Several species are known, the remains of which were discovered in the Lower Cretaceous (Aptian-Albian) of Brazil, North Africa, and possibly Mexico, as well as in the Upper Cretaceous of Morocco (Cenomanian), Madagascar and France. The Axelrodichthys of the Lower Cretaceous frequented both brackish and coastal marine waters while the most recent species lived exclusively in fresh waters. The French specimens are the last known fresh water coelacanths. Most of the species of this genus reached 1 metre to 2 metres in length. Axelrodichthys was named in 1986 by John G. Maisey in honor of the American ichthyologist Herbert R. Axelrod.

<i>Mawsonia</i> (fish) Extinct genus of coelacanths

Mawsonia is an extinct genus of prehistoric coelacanth fish. It is amongst the largest of all coelacanths, with one quadrate specimen possibly belonging to an individual measuring 5.3 metres in length. It lived in freshwater and brackish environments from the late Jurassic to the mid-Cretaceous of South America, eastern North America, and Africa. Mawsonia was first described by British paleontologist Arthur Smith Woodward in 1907.

Caririemys is an extinct genus of side-necked turtles, belonging to the Pelomedusoides of the family Euraxemydidae. The type species is C. violetae. A single fossil of an individual was found in the Santana Formation in Brazil, an 80-million-year-old Late Cretaceous deposit that has so far preserved other fossil reptiles such as dinosaurs and crocodilians.

<i>Cearachelys</i> Extinct genus of turtles

Cearachelys is an extinct genus of pleurodiran turtle which existed some 110 million years ago. The genus is monotypic, with only type species Cearachelys placidoi known.

<i>Tharrhias</i>

Tharrhias is an extinct genus of prehistoric bony fish that lived during the Aptian stage of the Early Cretaceous epoch. The type species T. araripis is named after the Araripe Basin, in which it was found in sediments of the Santana Formation.

<i>Araripichthys</i> Extinct genus of ray-finned fishes

Araripichthys is an extinct genus of marine ray-finned fish that lived from the Aptian to Coniacian stages of the Cretaceous period. The genus is named after the Araripe Basin, where it was found in the Crato and Santana Formations. Other fossils of the genus have been found at Goulmima in Morocco, the Tlayua Formation of Mexico and the Apón Formation of Venezuela.

<span class="mw-page-title-main">Araripe Basin</span> Rift Basin in brazil famous for its pterosaur fossils

The Araripe Basin is a rift basin covering about 8,000 square kilometres (3,100 sq mi), in Ceará, Piauí and Pernambuco states of northeastern Brazil. It is bounded by the Patos and Pernambuco lineaments, and is situated east of the Parnaíba Basin, southwest of the Rio do Peixe Basin and northwest of the Tucano and Jatobá Basins.

<span class="mw-page-title-main">Santana Group</span>

The Santana Group is a geologic group, formerly included as the middle part of the Araripe Group, in the Araripe Basin of northeastern Brazil. The group comprises the Crato, Ipubi and Romualdo Formations and is dated to the Aptian to Albian stages of the Early Cretaceous. The formations of the group were deposited in a lacustrine to subtidal shallow marine environment in the Araripe rift basin.

<span class="mw-page-title-main">Ipubi Formation</span>

The Ipubi Formation is the middle geological formation of the Santana Group, the middle part of the Araripe Group, in the Araripe Basin of northeastern Brazil. The formation is dated to the Aptian to Albian stages of the Early Cretaceous, unconformably overlying the Crato Formation and unconformably overlain by the Romualdo Formation, formerly known as the Romualdo Member of the Santana Formation. The averaging 15 metres (49 ft) thick Ipubi Formation comprises shales and sandstones in the lower section and evaporites in the upper part of the formation, deposited in a transgressive to highstand lacustrine environment in the Araripe rift basin.

<span class="mw-page-title-main">Riachuelo Formation</span> Geologic formation in Brazil

The Riachuelo Formation is a geologic formation of the Early to Late Cretaceous age in northeastern Brazil's Sergipe-Alagoas Basin. It is the first Formation of the Basin to contain sediments deposited under fully marine conditions. The formation is subdivided into three members: Angico, Taquari and Maruim.

References

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  2. Froese, Rainer, and Daniel Pauly, eds. (2009). "Characidae" in FishBase . January 2009 version.
  3. Froese, Rainer and Pauly, Daniel, eds. (2009). Species of Serrasalmus in FishBase . January 2009 version.
  4. Froese, Rainer and Pauly, Daniel, eds. (2009). Species of Pygocentrus in FishBase . January 2009 version.
  5. Martilla, David M.; Paulo M. Brito; Jane Washington-Evans (2008-02-16). "Mass mortality of fishes in the Santana Formation (Lower Cretaceous, ?Albian) of northeast Brazil". Cretaceous Research. 29 (4): 649–658. Bibcode:2008CrRes..29..649M. doi:10.1016/j.cretres.2008.01.012.
  6. Forey, Peter L.; Alison Longbottom; Martha Richter (2008). Fishes and the Break-up of Pangaea . Special Publication No 295. Geological Society. pp.  372. ISBN   9781862392489.
  7. Silva Santos, R. (1958). "Leptolepis diasii, novo peixe fóssil da Serra do Araripe, Brasil". Boletim da Divisão de Geologia e Mineralogia do Departamento Nacional de Produção Mineral, Notas Preliminares (in Portuguese). 108: 1–15.
  8. Maisey, J. (1991). Santana fossils, an illustrated atlas. Neptune City, New Jersey, USA: T.F.H. Publications.
  9. Silva Santos, R. (1991). Fósseis do nordeste do Brasil, paleoictiofáunula da Chapada do Araripe. Rio de Janeiro, Brazil: Universidade do Estado do Rio de Janeiro.
  10. Silva Santos, R. (1995). "Santanichthys, novo epíteto genérico para Leptolepis diasii Silva Santos, 1958 (Pisces, Teleostei) da Formação Santana (Aptiano), Bacia do Araripe, NE do Brasil". Anais da Academia Brasileira de Ciências (in Portuguese). 67: 249–258.