Atlanticopristis

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Atlanticopristis
Temporal range: Middle Cretaceous, (Cenomanian)
100.5–93.9  Ma
Atlanticopristis by PaleoGeek.png
Hypothetical life reconstruction based on relatives
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Rajiformes
Family: Sclerorhynchidae
Genus: Atlanticopristis
Pereira & Medeiros, 2008
Species:
A. equatorialis
Binomial name
Atlanticopristis equatorialis
Pereira & Medeiros, 2008

Atlanticopristis (meaning "Atlantic saw") is an extinct genus of sclerorhynchid (a sawfish-like chondrichthyan) that lived during the Middle Cretaceous (Cenomanian) of what is now the Northeast Region of Brazil, between 100.5 and 93.9 million years ago. Fourteen fossil teeth from Atlanticopristis were found in the Alcântara Formation, and referred to the closely related Onchopristis in 2007; a redescription in 2008 by Brazilian paleontologists Manuel Medeiros and Agostinha Pereira assigned it to a new genus containing one species, Atlanticopristis equatorialis.

Like all sawfish, it would have had a long snout armed with modified fish scales shaped into "teeth", but Atlanticopristis's teeth had barbs on both sides. Atlanticopristis inhabited fresh to brackish water estuaries near large conifer forests, and lived in the same time and place as many species of bony fish, cartilaginous fish, and lobe finned fish, as well as some crocodilians, and several dinosaurs. Many of the taxa present in the Alcântara Formation are also known from the Middle Cretaceous Kem Kem Beds in Morocco, due to the past connection of South America and Africa into the supercontinent Gondwana.

Discovery and naming

Fossils of Atlanticopristis were discovered in the Maranhão state of northeastern Brazil, at the Alcântara Formation of the Itapecuru Group on Cajual Island. The formation, composed of Cretaceous sediments, outcrops at the coastline of the São Marcos Bay, and documents the separation of South America and Africa; while presenting a large quantity and variety of continental and marine vertebrates. Fossils from the Alcântara Formation are highly diverse and plentiful, yet often fragmentary. [1] [2] [3] [4] Fourteen rostral teeth from Atlanticopriostis were brought back from the Falésia do Sismito exposure; due to the fact that sawfish are made of cartilage, their skeletons do not fossilize easily, so most remains found consist of the teeth from their snouts. The specimens of Atlanticopristis are currently housed at the Centro de Pesquisa de História Natural e Arqueologia do Maranhão (Archaeology and Natural History Research Center of Maranhão), in São Luís. [1]

The holotype tooth (CPHNAMA-VT 1174) was designated as such for being the most complete and well preserved specimen. Additionally, several specimens were assigned as paratypes: CPHNAMA-VT 1086, a single tooth and the largest specimen; CPHNAMA-VT 1085, two complete teeth; CPHNAMA-VT 1088 and CPHNAMA-VT 1173, two groups of four incomplete teeth each, all missing the tip of the crown; and CPHNAMA-VT 1173, two partial specimens with most of the crown. [1]

Portuguese paleontologists Manuel Medeiros and Agostinha Pereira described the material in 2008. The genus contains one species, Atlanticopristis equatorialis. The generic name referring to the Atlantic Ocean, in which most sediments of the Alcântara Formation were deposited, and "pristis" being the Greek word for "saw". The specific name "equatorialis" was chosen due to the discovery site being in close proximity to the equator. [1]

Description

Denticle comparison with three other sclerorhynchid species, as well as the sawfish, Pristis pristis (Atlanticopristis in blue) Sawfish Teeth Comparison by PaleoGeek.svg
Denticle comparison with three other sclerorhynchid species, as well as the sawfish, Pristis pristis (Atlanticopristis in blue)

The teeth on the rostrum (snout) of Atlanticopristis have a varied number of barbs at the front and rear margins. They are also laterally compressed, with both sides displaying thin enamel ridges extending outward from the base of the tooth, forming a fan shape. Some of the teeth also have grooves running down their length on both sides. The peduncle (or base) of the tooth is enlarged, and covered in irregular ridges, the bottom is typically concave, having a sub-rectangular or ellipsoid shape. [1]

The specimens range in size from 11.5 mm (0.45 inches) to 18.8 mm (0.74 inches). The holotype (CPHNAMA-VT 1174) is 15 mm (0.59 inches) in length, including the peduncle; which itself is 6.3 mm (0.24 inches) wide, and 3 mm (0.11 inches) long. It has a thickness of 3 mm (0.11 inches). The barb number on all specimens ranges from two to four barbs at the front margin and four to five at the rear, some specimens like CPHNAMA-VT 1085 having vestigial bumps that could be considered additional barbs. [1]

Onchopristis numidus tooth, displaying the same enamel ribbing found in Atlanticopristis Onchopristis numidus 052013.JPG
Onchopristis numidus tooth, displaying the same enamel ribbing found in Atlanticopristis

Sawfish evolved long snouts armed with rows of teeth on both sides, although these spines do not represent true teeth, but highly modified fish scales, or dermal denticles. [5] This adaptation could be related to their feeding habits, such as sifting through sand/mud to search for food or to slash at prey. Like extant sawsharks, these spines were attached to the rostrum of sclerorhynchids like Atlanticopristis using ligaments, compared to modern sawfish which have their teeth attached via alveoli (tooth sockets). The longitudinal ribbing, or ridges, of enameloid that can be seen on sclerorhynchid teeth would have aided in the attachment of these ligaments. [1]

Classification

Pristiophorids, like this Japanese sawshark, are similar in dentition to Mesozoic sclerorhynchids, but are not close relatives. Pristiophorus japonicus cropped.jpg
Pristiophorids, like this Japanese sawshark, are similar in dentition to Mesozoic sclerorhynchids, but are not close relatives.

Atlanticopristis belongs to the Sclerorhynchidae, a possibly monophyletic [6] family of Cretaceous sawfish-like chondrichthyans dating from the Early to Late epochs of the Cretaceous Period. The fossilized teeth of Atlanticopristis had previously been referred to an indeterminate species of Onchopristis in 2007 by Pereira and Medeiros, based on the shape of the peduncle, the presence of multiple barbs, and the enamel ribbing. [2] In 2008 the teeth were assigned to a new genus based on the lack of an intermediate form between Atlanticopristis and Onchopristis, as well as morphological differences that distinguish it from other sclerorhynchids. Pereira and Medeiros also stated that Atlanticopristis is so closely related to Onchopristis that, "any other subjective interpretation could consider them as synonyms." The barb number on the spines of Atlanticopristis more closely resembles that of Onchopristis dunklei than Onchopristis numidus, as O. numidus usually has no more than a single barb, while O. dunklei always has more than one. The sclerorhynchid Borodinopristis , also has multibarbed teeth, but is too distinct in all other aspects to suggest a close relation. [1]

The formation of multiple barbs on both sides of the teeth is a characteristic also seen in the extinct Australian sawshark Ikamauius. In general, sclerorynchids all developed dentition closer to that of sawsharks than modern sawfish, but they are more closely related to the latter. This similarity is considered a case of convergent evolution, where unrelated organisms evolve analogous traits. [1]

Atlanticopristis and Onchopristis exhibit similarities to a Bolivian species of sclerorhynchid Pucapristis branisi, such as the enamel ribbing and the formation of a barb on the posterior margin, however, their peduncles differ greatly. In 1987, French paleoichthyologist Henri Cappeta distinguished two groups inside of sclerorhynchidae, separating Onchopristis from Pucapristis. [1]

Paleoecology

Like Onchopristis (model pictured), Atlanticopristis coexisted with spinosaurids Spinosaurus attacking Onchopristis.jpg
Like Onchopristis (model pictured), Atlanticopristis coexisted with spinosaurids

Atlanticopristis originates from the Alcântara Formation, which is dated to the Cenomanian stage of the Middle Cretaceous Period, sometime between 100.5 and 93.9 million years ago. [3] Like most modern sawfishes, [7] it inhabited an estuarine environment of fresh to brackish water. Atlanticopristis likely came from the shallow marine regions of the southern Atlantic Ocean, and periodically entered estuarine waters. The area that is now Laje do Coringa locality would have comprised tidal estuaries of rivers and lagoons, alongside these would have been large forests of conifers, horsetails, and ferns. The animal would have shared its habitat with freshwater, marine, and estuarine fish like the closely related sclerorynchid Onchopristis numidus ; Mawsonia gigas , a large coelacanth; Myliobatis sp. (of uncertain species), a ray; as well as many species of bony fishes, ray-finned fishes, and lungfish. Marine invertebrates were prominent in the region, as shown by the many mollusc genera discovered in the deposits. Atlanticopristis remains have also been found in association with those of land-based animals like crocodilians and dinosaurs, [3] [1] among these are two members of Spinosauridae (a family of crocodile-like dinosaurs); Oxalaia quilombensis , and Spinosaurus sp. An indeterminate Carcharodontosaurus species is known from the deposits, along with other small-to-medium-sized theropods, and the mesoeucrocodylian Coringasuchus anisodontis . [3]

The paleoecological situation in Cenomanian Brazil highly resembles that of Middle Cretaceous north Africa, particularly the Kem Kem and Bahariya Formations; many of the same biota can be found in both north Africa and northeastern Brazil. This is a result of Gondwana, a supercontinent that comprised Africa and South America, after their separation, the taxa on each landmass would have continued to evolve separately; contributing to small anatomical differences between the transoceanic taxa. [8]

Related Research Articles

<i>Spinosaurus</i> Genus of spinosaurid dinosaur

Spinosaurus is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago. The genus was known first from Egyptian remains discovered in 1912 and described by German palaeontologist Ernst Stromer in 1915. The original remains were destroyed in World War II, but additional material came to light in the early 21st century. It is unclear whether one or two species are represented in the fossils reported in the scientific literature. The best known species is S. aegyptiacus from Egypt, although a potential second species, S. maroccanus, has been recovered from Morocco. The contemporary spinosaurid genus Sigilmassasaurus has also been synonymized by some authors with S. aegyptiacus, though other researchers propose it to be a distinct taxon. Another possible junior synonym is Oxalaia from the Alcântara Formation in Brazil.

<i>Irritator</i> Spinosaurid theropod dinosaur genus from the Early Cretaceous Period

Irritator is a genus of spinosaurid dinosaur that lived in what is now Brazil during the Albian stage of the Early Cretaceous Period, about 113 to 110 million years ago. It is known from a nearly complete skull found in the Romualdo Formation of the Araripe Basin. Fossil dealers had acquired this skull and sold it to the State Museum of Natural History Stuttgart. In 1996, the specimen became the holotype of the type species Irritator challengeri. The genus name comes from the word "irritation", reflecting the feelings of paleontologists who found the skull had been heavily damaged and altered by the collectors. The species name is a homage to the fictional character Professor Challenger from Arthur Conan Doyle's novels.

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

Sawfish, also known as carpenter sharks, are a family of rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged in a way that resembles a saw. They are among the largest fish, with some species reaching lengths of about 7–7.6 m (23–25 ft). They are found worldwide in tropical and subtropical regions in coastal marine and brackish estuarine waters, as well as freshwater rivers and lakes. All species are endangered.

<i>Carcharodontosaurus</i> Genus of carcharodontosaurid dinosaur from the Cretaceous period

Carcharodontosaurus is a genus of carnivorous theropod dinosaur that lived in North Africa from about 99 to 94 million years ago during the Cenomanian stage of the Late Cretaceous. Two teeth of the genus, now lost, were first described from Algeria by French paleontologists Charles Depéret and Justin Savornin as Megalosaurus saharicus. A partial skeleton was collected by crews of German paleontologist Ernst Stromer during a 1914 expedition to Egypt. Stromer did not report the Egyptian find until 1931, in which he dubbed the novel genus Carcharodontosaurus, making the type species C. saharicus. Unfortunately, this skeleton was destroyed during the Second World War. In 1995 a nearly complete skull of C. saharicus, the first well-preserved specimen to be found in almost a century, was discovered in the Kem Kem Beds of Morocco; it was designated the neotype in 1996. Fossils unearthed from the Echkar Formation of northern Niger were described and named as another species, C. iguidensis, in 2007.

<span class="mw-page-title-main">Rajiformes</span> Order of fishes in the superorder Batoidea

Rajiformes is one of the four orders in the superorder Batoidea, flattened cartilaginous fishes related to sharks. Rajiforms are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the head and the gill slits are on the underside of the body. Most species give birth to live young, although some lay eggs enclosed in a horny capsule.

<span class="mw-page-title-main">Spinosauridae</span> Family of dinosaurs

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<i>Malawisaurus</i> Extinct genus of dinosaurs

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<i>Rebbachisaurus</i> Extinct genus of dinosaurs

Rebbachisaurus is a genus of sauropod dinosaur of the superfamily Diplodocoidea, that lived during the Late Cretaceous period in Africa and possibly also South America about 99-97 million years ago. Remains attributed to Rebbachisaurus have been found in Morocco, Niger, Algeria, Tunisia and possibly also Argentina, although only the Moroccan remains can be referred to the genus without doubt. The discovery of Rayososaurus, a South American sauropod nearly identical to Rebbachisaurus which may have actually have been the same animal as Rebbachisaurus, supports the theory that there was still a land connection between Africa and South America during the Early Cretaceous, long after it was commonly thought the two continents had separated.

<i>Sigilmassasaurus</i> Spinosaurid theropod dinosaur genus from Cretaceous Period

Sigilmassasaurus is a controversial genus of spinosaurid dinosaur that lived approximately 100 to 94 million years ago during the Late Cretaceous Period in what is now northern Africa. Named in 1996 by Canadian paleontologist Dale Russell, it contains a single species, Sigilmassasaurus brevicollis. The identity of the genus has been debated by scientists, with some considering its fossils to represent material from the closely related species Spinosaurus aegyptiacus, while others have classified it as a separate taxon, forming the clade Spinosaurini with Spinosaurus as its sister taxon.

<i>Protosphyraena</i> Extinct genus of fishes

Protosphyraena is a fossil genus of swordfish-like marine fish, that thrived worldwide during the Upper Cretaceous Period (Coniacian-Maastrichtian). Though fossil remains of this taxon have been found in both Europe and Asia, it is perhaps best known from the Smoky Hill Member of the Niobrara Chalk Formation of Kansas. Protosphyraena was a large fish, averaging 2–3 metres in length. Protosphyraena shared the Cretaceous oceans with aquatic reptiles, such as mosasaurs and plesiosaurs, as well as with many other species of extinct predatory fish. The name Protosphyraena is a combination of the Greek word protos ("early") plus Sphyraena, the genus name for barracuda, as paleontologists initially mistook Protosphyraena for an ancestral barracuda. Recent research shows that the genus Protosphyraena is not at all related to the true swordfish-family Xiphiidae, but belongs to the extinct family Pachycormidae.

<span class="mw-page-title-main">Kem Kem Group</span> Geological group in eastern Morocco

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<i>Oxalaia</i> Extinct genus of dinosaurs

Oxalaia is a genus of spinosaurid dinosaur that lived in what is now the Northeast Region of Brazil during the Cenomanian stage of the Late Cretaceous period, sometime between 100.5 and 93.9 million years ago. Its only known fossils were found in 1999 on Cajual Island in the rocks of the Alcântara Formation, which is known for its abundance of fragmentary, isolated fossil specimens. The remains of Oxalaia were described in 2011 by Brazilian palaeontologist Alexander Kellner and colleagues, who assigned the specimens to a new genus containing one species, Oxalaia quilombensis. The species name refers to the Brazilian quilombo settlements. Oxalaia quilombensis is the eighth officially named theropod species from Brazil and the largest carnivorous dinosaur discovered there. It is closely related to the African genus Spinosaurus, and/or may be a junior synonym of this taxon.

The Alcântara Formation is a geological formation in northeastern Brazil whose strata date back to the Cenomanian of the Late Cretaceous.

<i>Onchopristis</i> Extinct genus of cartilaginous fishes

Onchopristis is an extinct genus of sclerorhynchoid from the Cretaceous of North Africa, Europe, and North America. Its name is derived from the Ancient Greek ónkos and prístis. It contains two valid species, O. numida and O. dunklei, though some researchers argue that both may be considered a single taxon with variation in morphology caused by a wide geographical range. Specimens of Onchopristis have been discovered in coastal and fluvial deposits dated from the Barremian to the Cenomanian age, making this genus one of the oldest and longest-lived sclerorhynchoid genera.

The Aoufous Formation is a geological formation that contains some of the vertebrate assemblage of the Kem Kem Group, of Late Cretaceous date. Two other formations comprise the Kem Kem beds: the underlying Ifezouane Formation and the overlying Akrabou Formation.

<i>Onchosaurus</i> Extinct genus of cartilaginous fishes

Onchosaurus is an extinct genus of sclerorhynchid sawskate from the Late Cretaceous. Its fossils have been found in the Cretaceous sediments of Egypt, Brazil, Congo, Morocco, France, Niger, Japan, Chile, Peru and the United States.

<span class="mw-page-title-main">Sclerorhynchoidei</span> Extinct suborder of cartilaginous fishes

Sclerorhynchoidei is an extinct suborder of rajiform rays that had long rostra with large denticles similar to sawfishes and sawsharks. This feature was convergently evolved and their closest living relatives are actually skates. While they are often called "sawfishes", sawskates is a more accurate common name for sclerorhynchoids. The suborder contains five named families: Ganopristidae, Ischyrhizidae, Onchopristidae, Ptychotrygonidae, and Schizorhizidae. Several genera are not currently placed in any of these families. Sclerorhynchoids first appeared in the Barremian and went extinct during the Cretaceous–Paleogene extinction event, with former Paleocene occurrences being misidentifications or reworked specimens. One female specimen of Libanopristis with nine embryos preserved in situ represents one of the first fossil evidence of batoid ovoviviparity.

Itapeuasaurus is a genus of rebbachisaurid sauropod dinosaur from the Alcântara Formation of Maranhão in Brazil. The type and only species is Itapeuasaurus cajapioensis. It is the most complete Cenomanian-aged diplodocoid known from South America and it is also the first reported Cenomanian-aged rebbachisaurid discovered in South America.

Australopristis is an extinct genus of rajiform ray from the late Cretaceous epoch. Its name is derived from the Latin for "southern" and the Greek for "saw". It is known from a single species, A. wiffeni named for the late prominent fossil hunter Joan Wiffen. This species is currently known only from rostral teeth found at Mangahouanga stream and East Wing, Haumuri bluff, New Zealand. Its rostral teeth possess a smooth root which makes it unique among Sclerorhynchids. Rostral teeth appear to vary in morphology according to position and ontogenetic stage. Unlike the related Onchopristis and Atlanticopristis, it lives in a marine rather than fluvial environment and likely preferred cooler waters.

Baharipristis is an extinct genus of sawskate from the Cretaceous period. It contains a singular species, B. bastetiae. It was described from the Cenomanian-aged Bahariya formation of Gebel Ghorabi, Egypt based on distinctive isolated rostral teeth. It shares the formation with at least 9 other genera of Sclerorhynchid Saw-snouted sharks.

References

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