Atlanticopristis

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Atlanticopristis
Temporal range: Late 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
Order: Rajiformes
Suborder: Sclerorhynchoidei
Genus: Atlanticopristis
Pereira & Medeiros, 2008
Species:
A. equatorialis
Binomial name
Atlanticopristis equatorialis
Pereira & Medeiros, 2008

Atlanticopristis (meaning "Atlantic saw") is an extinct genus of sclerorhynchoid that lived during the Late Cretaceous (Cenomanian) of what is now the Northeast Region of Brazil, between 100.5 and 93.9 million years ago. It contains a single species, Atlanticopristis equatorialis, originally assigned to the closely related genus Onchopristis .

Contents

Similar to modern sawfish, it would have had a long snout armed with modified fish scales shaped into "teeth", but the rostral denticles of Atlanticopristis 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 same-aged Kem Kem Beds in Morocco, due to the past connection of South America and Africa into the supercontinent Gondwana.

Discovery and naming

In 2007, fourteen rostral denticles which were discovered in the Maranhão state of northeastern Brazil, at the Alcântara Formation of the Itapecuru Group on Cajual Island, were referred to as Onchopristis sp. based on the shape of the peduncle, the presence of multiple barbs, and the enamel ribbing. [1]

In 2008, the Portuguese paleontologists Manuel Medeiros and Agostinha Pereira assigned the fourteen rostral denticles to their own genus and species, Atlanticopristis equatorialis, based on the lack of an intermediate form between Atlanticopristis and Onchopristis, as well as morphological differences that distinguish it from other sclerorhynchoids. 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. [2]

The fossils were brought back from the Falésia do Sismito exposure, but because the bones of sclerorhynchoids 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. 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. [2]

Description

Denticle comparison with three other sclerorhynchoid species, as well as the sawfish, Pristis pristis (Atlanticopristis in blue) Sawfish Teeth Comparison by PaleoGeek.svg
Denticle comparison with three other sclerorhynchoid 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. [2]

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. [2]

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

Sawfish and sawsharks 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. [3] This adaptation could be related to their feeding habits, such as sifting through sand/mud to search for food or to slash at prey. Likewise, these spines were attached to the rostrum of sclerorhynchoids 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 sclerorhynchoid teeth would have aided in the attachment of these ligaments. [2]

Classification

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

Atlanticopristis belongs to the Sclerorhynchoidei, an extinct suborder of rajiform rays during the Cretaceous period that had long rostra with large denticles similar to sawfishes and sawsharks. This feature was convergently evolved, recently proposed as 'pristification', [4] and their closest living relatives are actually skates. [5] While Pereira and Medeiros (2008) assigned Atlanticopristis to the family Sclerorhynchidae and considered it to be very closely related to Onchopristis, [2] recent phylogenetic analyses suggest that Onchopristis belongs to its own monotypic family Onchopristidae, and that Atlanticopristis does not belong to the sclerorhynchids. [4] [5]

The barb number on the spines of Atlanticopristis more closely resembles that of Onchopristis dunklei than Onchopristis numida, as O. numida usually has no more than a single barb, while O. dunklei always has more than one. The sclerorhynchoid Borodinopristis , also has multibarbed teeth, but is too distinct in all other aspects to suggest a close relation. The formation of multiple barbs on both sides of the teeth is a characteristic also seen in the extinct Australian sawshark Ikamauius. In general, sclerorynchoids all developed dentition closer to that of sawsharks than modern sawfish, but they are more closely related to the skates. This similarity is considered a case of convergent evolution, where unrelated organisms evolve analogous traits. [2] [4] [5]

Atlanticopristis and Onchopristis exhibit similarities to a Bolivian species of sclerorhynchoid 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 within sclerorhynchoids, separating Onchopristis from Pucapristis. [2]

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 Late Cretaceous, sometime between 100.5 and 93.9 million years ago. [6] 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. [2] [7] [6] [8] The describers of Atlanticopristis suggested that the taxon 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. [2]

Atlanticopristis would have shared its habitat with freshwater, marine, and estuarine fish like the closely related sclerorynchoid Onchopristis cf. O. numida, [9] the large coelacanth Mawsonia gigas , the ray Myliobatis sp. and numerous species of bony fishes, ray-finned fishes, lungfish and marine invertebrates which were prominent in the region, as shown by the many mollusc genera discovered in the deposits. [2] Its remains have also been found in association with those of land-based animals like crocodilians and dinosaurs, including the spinosaurid Oxalaia quilombensis along with other indeterminate theropods and the mesoeucrocodylian Coringasuchus anisodontis . [6] [2]

The paleoecological situation in Cenomanian Brazil highly resembles that of Cenomanian North Africa, particularly the Kem Kem Beds and Bahariya Formation, where many of the same or similar biota can be found in both regions. Researchers have suggested that after the separation of Gondwana, a supercontinent that included Africa and South America, the taxa on each landmass would have continued to evolve separately, contributing to small anatomical differences between the transoceanic taxa. [10]

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 stage of the Late Cretaceous period, about 100 to 94 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 type species S. aegyptiacus is mainly known from Egypt and Morocco. Although a potential second dubious species, S. maroccanus, has been recovered from Morocco, this dubious species is likely a junior synonym of S. aegyptiacus. Other possible junior synonyms include Sigilmassasaurus from the Kem Kem beds in Morocco and Oxalaia from the Alcântara Formation in Brazil, though other researchers propose both genera to be distinct taxa.

<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 critically 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 100 to 94 million years ago during the Cenomanian age of the 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 clade Batomorphi, often referred to as 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.

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

Sclerorhynchus is an extinct genus of ganopristid sclerorhynchoid that lived during the Late Cretaceous. The genus Ganopristis is considered a junior synonym of Sclerorhynchus. It was a widespread genus, with fossils found in the Middle East, North Africa, Europe, and North America. While it had a long rostrum with large denticles similar to sawfishes and sawsharks, its closest living relatives are actually skates. Complete specimens of S. atavus show that its fin arrangement was similar to skates, with the pectoral and pelvic fins touching, both dorsal fins located behind the pelvic fins, and a reduced caudal fin.

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

Schizorhiza is an extinct genus of schizorhizid sclerorhynchoid that lived during the Late Cretaceous. It contains one valid species, Schizorhiza stromeri. It lived from the Campanian to Maastrichtian, and its fossils have been found in Africa, the Middle East, North America, and South America.

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

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

Onchopristis is an extinct genus of sclerorhynchoid from the Cretaceous of North Africa, Europe, North America, and potentially South America. 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 ages, making this genus one of the oldest known sclerorhynchoid.

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Australopristis is an extinct genus of sclerorhynchoid fish 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 sclerorhynchoids. 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.

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References

  1. Pereira, A.A.; Medeiros, M.A. (2007). "A new Elasmobranchii form from the Alcântara Formation (Itapecuru deposits; Eocenomanian of Brazil". Congresso Brasileiro de Paleontologia. Vol. 20. Boletim de Resumos, UNB Brasília. p. 18.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 Pereira, A. A.; Medeiros, M. A. (2008). "A new sclerorhynchiform (Elasmobranchii) from the middle Cretaceous of Brazil". Revista Brasileira de Paleontologia. 11 (3): 207–212. doi: 10.4072/rbp.2008.3.07 .
  3. Welten, M.; Smith, M. M.; Underwood, C.; Johanson, Z. (September 2015). "Evolutionary origins and development of saw-teeth on the sawfish and sawshark rostrum (Elasmobranchii; Chondrichthyes)". Royal Society Open Science. 2 (9): 150189. Bibcode:2015RSOS....250189W. doi:10.1098/rsos.150189. PMC   4593678 . PMID   26473044.
  4. 1 2 3 Greenfield, T. (2024). "Pristification: Defining the convergent evolution of saws in sharks and rays (Chondrichthyes, Neoselachii)". Mesozoic. 1 (2): 121–124. doi:10.11646/MESOZOIC.1.2.3.
  5. 1 2 3 Villalobos-Segura, E.; Kriwet, J.; Vullo, R.; Stumpf, S.; Ward, D.J.; Underwood, C.J. (2021). "The skeletal remains of the euryhaline sclerorhynchoid †Onchopristis (Elasmobranchii) from the 'Mid'-Cretaceous and their palaeontological implications". Zoological Journal of the Linnean Society. 193 (2): 746–771. doi:10.1093/zoolinnean/zlaa166.
  6. 1 2 3 Medeiros, Manuel Alfredo; Lindoso, Rafael Matos; Mendes, Ighor Dienes; Carvalho, Ismar de Souza (August 2014). "The Cretaceous (Cenomanian) continental record of the Laje do Coringa flagstone (Alcântara Formation), northeastern South America". Journal of South American Earth Sciences. 53: 50–58. Bibcode:2014JSAES..53...50M. doi:10.1016/j.jsames.2014.04.002. ISSN   0895-9811.
  7. Medeiros, Manuel; Carvalho Freire, Pedro; Pereira, Agostinha; Anderson Barros Santos, Ronny; Lindoso, Rafael; Flávia Amaral Coêlho, Ana; Brandão Passos, Emanuel; Sousa Melo Júnior, Emilio (2007). "Another African dinosaur recorded in the Eocenomanian of Brazil and a revision on the paleofauna of the Laje do Coringa site". Paleontologia: Cenários De Vida. Vol. 1. Editora Interciência. pp. 413–423. ISBN   9788571931848.
  8. Kellner, Alexander W. A.; Azevedeo, Sergio A. K.; Machado, Elaine B.; Carvalho, Luciana B.; Henriques, Deise D. R. (2011). "A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil" (PDF). Anais da Academia Brasileira de Ciências. 83 (1): 99–108. doi: 10.1590/S0001-37652011000100006 . ISSN   0001-3765. PMID   21437377.
  9. Pereira, A.A.; Medeiros, M.A. (2003). "Novas ocorrências de peixes no Eocenomaniano do Maranhão". Congresso Brasileiro de Paleontologia. Vol. 18. Boletim de Resumos, UNB Brasília. pp. 221–222.
  10. Candeiro, Carlos Roberto A. (August 2015). "Middle Cretaceous dinosaur assemblages from northern Brazil and northern Africa and their implications for northern Gondwanan composition". Journal of South American Earth Sciences. 61: 147–153. Bibcode:2015JSAES..61..147C. doi:10.1016/j.jsames.2014.10.005. ISSN   0895-9811.