''Atlanticopristis'' (meaning "Atlantic saw") is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of sclerorhynchoid that lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

(

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

) of what is now the Northeast Region of Brazil, between 100.5 and 93.9

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

. It contains a single species, ''Atlanticopristis equatorialis'', originally assigned to the closely related genus ''

Onchopristis ''Onchopristis'' is an extinct genus of Sclerorhynchoidei, sclerorhynchoid, or sawskate, from the Cretaceous of North Africa, Europe, North America, and potentially South America. It contains two valid species, ''O. numida'' and ''O. dunklei'', t ...

''. Similar to modern sawfish, it would have had a long snout armed with modified

fish scale A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

s shaped into "teeth", but the rostral denticles of ''Atlanticopristis'' had barbs on both sides. ''Atlanticopristis'' inhabited fresh to

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

water

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

near large

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

forests, and lived in the same time and place as many species of

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

cartilaginous fish Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

, and lobe finned fish, as well as some

crocodilia Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...

ns, and several

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s. Many of the

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

present in the Alcântara Formation are also known from the same-aged

Kem Kem Beds The Kem Kem Group (commonly known as the Kem Kem beds) is a geological group in the Kem Kem region of eastern Morocco, whose strata date back to the Cenomanian stage of the Late Cretaceous. Its strata are subdivided into two geological formations ...

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

, due to the past connection of South America and Africa into the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

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 ...

Discovery and naming

In 2007, fourteen rostral denticles which were discovered in the

Maranhão Maranhão () is a States of Brazil, state in Brazil. Located in the country's Northeast Region, Brazil, Northeast Region, it has a population of about 7 million and an area of and it is divided into 217 municipalities. Clockwise from north, it ...

state of northeastern Brazil, at the

Alcântara Formation The Alcântara Formation is a geological Formation (geology), formation in Northeast Region, Brazil, northeastern Brazil whose strata date back to the Cenomanian of the Late Cretaceous. Fossil content Dinosaurs Sauropods Theropods ...

of the Itapecuru Group on

Cajual Island The island of Cajual is located in the Baía de São Marcos near to Alcântara, Maranhão, Brazil. The island is an important Brazilian paleontological site, where fossils of animals such as ''Spinosaurus'' and ''Sigilmassasaurus'' were found, a ...

, were referred to as ''Onchopristis'' sp. based on the shape of the peduncle, the presence of multiple barbs, and the enamel ribbing. In 2008, the Portuguese

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

s 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 The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

, in which most

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s of the Alcântara Formation were deposited, and "''pristis"'' being the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word for "saw". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''"equatorialis"'' was chosen due to the discovery site being in close proximity to the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. The fossils were brought back from the Falésia do Sismito exposure, but because the bones of sclerorhynchoids are made of

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

, 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

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...

s: 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.

Description

The teeth on the

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

(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. The specimens range in size from 11.5 mm (0.45 inches) to 18.8 mm (0.74 inches). The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

(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. Onchopristis_numidus_052013

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 A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

. 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

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

s, compared to modern sawfish which have their teeth attached via

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

(tooth sockets). The longitudinal ribbing, or ridges, of

enameloid Enameloid, also known as durodentine or vitrodentine, is an enamel-like tissue found in fish. It is the primary outer component of shark odontodes (teeth and dermal denticles), and modified forms of enameloid also occur in the teeth and scales of ...

that can be seen on sclerorhynchoid teeth would have aided in the attachment of these ligaments.

Classification

''Atlanticopristis'' belongs to the

Sclerorhynchoidei Sclerorhynchoidei is an extinct suborder of Rajiformes, rajiform Batoidea, rays that had long Rostrum (anatomy)#Vertebrates, rostra with large Fish scale#Placoid scales, denticles similar to Sawfish, sawfishes and Sawshark, sawsharks. This featu ...

, an extinct suborder of rajiform

rays Ray or RAY may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), the bony or horny spine on ray-finned fish Science and mathematics * Half-line (geometry) or ray, half of a line split at an ...

during the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period that had long

rostra The Rostra () was a large platform built in the city of Rome that stood during the republican and imperial periods. Speakers would stand on the rostra and face the north side of the Comitium towards the senate house and deliver orations to t ...

with large denticles similar to

sawfishes Sawfish, also known as carpenter sharks, are a Family (biology), family of very large batoidea, rays characterized by a long, narrow, flattened rostrum (anatomy), rostrum, or nose extension, lined with sharp transverse plane, transverse teeth, ...

and

sawsharks A sawshark or saw shark is a member of a shark order (Pristiophoriformes ) bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey. There are eight species within the Pristio ...

. This feature was

convergently evolved Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

, recently proposed as 'pristification', and their closest living relatives are actually skates. While Pereira and Medeiros (2008) assigned ''Atlanticopristis'' to the family Sclerorhynchidae and considered it to be very closely related to ''Onchopristis'', recent phylogenetic analyses suggest that ''Onchopristis'' belongs to its own monotypic family Onchopristidae, and that ''Atlanticopristis'' does not belong to the sclerorhynchids. 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 A sawshark or saw shark is a member of a shark order (Pristiophoriformes ) bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey. There are eight species within the Pristi ...

Ikamauius ''Ikamauius'' is an extinct genus of sawshark from the Cenozoic of New Zealand. It contains a single species, ''I. ensifer''. It is most closely related to the extant ''Pliotrema ''Pliotrema'' is a genus of sawsharks found in the Western India ...

.'' 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 Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

, where unrelated organisms evolve analogous traits. ''Atlanticopristis'' and ''Onchopristis'' exhibit similarities to a Bolivian species of sclerorhynchoid ''

Pucapristis ''Pucapristis'' is a prehistoric genus of sclerorhynchoid ray whose fossils first appear in the fossil record in rocks dating from the Maastrichtian stage. The genus was described in 1963 by Schaeffer.paleoichthyologist Fish began evolving about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish linea ...

Henri Cappetta, Henri Cappeta distinguished two groups within sclerorhynchoids, separating ''Onchopristis'' from ''Pucapristis''.

Paleoecology

''Atlanticopristis'' originates from the Alcântara Formation, which is dated to the

Stage (geology), stage of the

, sometime between 100.5 and 93.9

. 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. 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. ''Atlanticopristis'' would have shared its habitat with freshwater, marine, and estuarine fish like the closely related sclerorynchoid ''

'' cf. ''O. numida'', 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 Mollusca, mollusc genera discovered in the deposits. Its remains have also been found in association with those of land-based animals like

ns and dinosaurs, including the Spinosauridae, spinosaurid ''Oxalaia quilombensis'' along with other indeterminate theropods and the mesoeucrocodylian ''Coringasuchus anisodontis''. The paleoecological situation in Cenomanian Brazil highly resembles that of Cenomanian North Africa, particularly the

and Bahariya Formation, where many of the same or similar biota (ecology), biota can be found in both regions. Researchers have suggested that after the separation of

, a

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.

References

{{Taxonbar, from=Q55604442 Sclerorhynchoidei Monotypic prehistoric cartilaginous fish genera Late Cretaceous cartilaginous fish Cenomanian genera Late Cretaceous fish of South America Cretaceous Brazil Fossils of Brazil Fossil taxa described in 2008