Oxalaia

Oxalaia (in reference to the African deity Oxalá) is a genus of spinosaurid theropod 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.

Although Oxalaia is known only from two partial skull bones, Kellner and colleagues found that its teeth and cranium had a few distinct features not seen in other spinosaurids or theropods, including two replacement teeth in each socket and a very sculptured secondary palate. Oxalaia's habitat was tropical, heavily forested, and surrounded by an arid landscape. This environment had a large variety of lifeforms also present in Middle-Cretaceous North Africa, due to the connection of South America and Africa as parts of the supercontinent Gondwana. As a spinosaurid, the traits of Oxalaia's skull and dentition indicate a partly piscivorous (fish-eating) lifestyle similar to that of modern crocodilians. Fossil evidence suggests spinosaurids also preyed on other animals such as small dinosaurs and pterosaurs.

Oxalaia
Temporal range: Late Cretaceous, (Cenomanian)
100.5–93.9 Ma
Holotype snout fossil of Oxalaia in right lateral view, left lateral view, ventral view, and slightly oblique ventral view
Holotype snout in multiple views
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Spinosauridae
Subfamily: Spinosaurinae
Genus: Oxalaia
Kellner et al., 2011
Type species
Oxalaia quilombensis
Kellner et al., 2011
Synonyms

Discovery and naming

Spinosaur Taxonomy Map
Map showing the Northeast Region of Brazil, with the discovery sites of three spinosaurine fossil specimens in the Araripe and São Luís-Grajaú Basins marked. From top to bottom: Oxalaia, Irritator, and Angaturama.

Oxalaia stems from the Alcântara Formation, a succession of sedimentary rocks that is part of the Itapecuru Group of the São Luís-Grajaú Basin, in northeastern Brazil. These rocks have been dated by scientists to the Cenomanian stage of the Late Cretaceous Period, 100.5 to 93.9 million years ago.[1][2] Outcropping at the northern coast of the formation, the Laje do Coringa locality is made up mostly of sandstones and mudstones, along with conglomerate rock layers containing fossil plant and vertebrate fragments.[3] These sediments were deposited under marine and fluvial conditions similar to those of the Bahariya Formation in Egypt, where Spinosaurus remains have been found.[1][4] In 1999, fossils of Oxalaia were recovered from the Laje do Coringa.[5] Palaeontologist Elaine Machado, of the National Museum of Rio de Janeiro, was surprised to find such a well-preserved fossil at the site and stated in a press release that "this is how most scientific discoveries happen, it was by accident".[6] The finding was a rare occurrence due to the erosive nature of the tides at the deposit, which are responsible for the fragmented state of most fossils in the bone bed; remains not found on site are often removed from the formation by wave action.[5] Generally, the majority of fossil remains found at the Alcântara Formation consist of teeth and isolated skeletal elements, of which the Laje do Coringa site has yielded hundreds.[1][5][7]

Oxalaia quilombensis
Diagram illustrating known jaw material in place

Oxalaia is one of three spinosaurids discovered in Brazil, the other two being Irritator and its possible synonym Angaturama, both of which were also initially known from partial skulls. They were discovered in the Romualdo Formation of the Santana Group, part of the Araripe Basin. Microfossils date this formation to the Albian, around nine to six million years before Oxalaia.[5][8][9] The fossil record of spinosaurids is poor compared to those of other theropod groups; very few body fossils are known and most genera have been erected from isolated elements such as vertebra or teeth.[10][11] The holotype specimen of Oxalaia quilombensis, designated MN 6117-V, was found in situ (at its original place of deposition) with part of the left side embedded in the rock matrix; it consists of the fused praemaxillae (frontmost snout bones) from a large individual. An isolated and incomplete left maxilla (main upper jaw bone) fragment (MN 6119-V) was referred to Oxalaia because it showed the same general traits occurring in spinosaurids, the maxilla was discovered on the rock surface, having possibly moved from its original location after erosion. Both bone fragments were found on Cajual Island, Maranhão, in the Northeast Region of Brazil, and were housed at the National Museum of Rio de Janeiro.[5] In 2018, a fire engulfed the palace housing the museum,[12] possibly destroying Oxalaia's specimens, along with various other fossils found in Brazil.[13] Besides the partial skull bones, numerous spinosaurid teeth had earlier been reported from the Laje do Coringa site.[5]

The discoveries of Oxalaia and of the Late Cretaceous reptiles Pepesuchus and Brasiliguana were announced in a presentation by the Brazilian Academy of Sciences in March 2011.[14][15] Machado described Oxalaia as "the dominant reptile of [what is now] Cajual Island". She stated that there is interest in spinosaurids in Brazil and abroad because of their debut in the Jurassic Park franchise and their distinctiveness among other carnivorous dinosaurs.[14] The species description of Oxalaia was written by Brazilian palaeontologists Alexander Kellner, Elaine Machado, Sergio Azevedo, Deise Henriques, and Luciana Carvalho. This paper, among many others, were composed into a volume of 20 works on prehistoric biodiversity that was published by the Academy in March 2011.[6] The type species Oxalaia quilombensis is the eighth officially named species of theropod from Brazil. The generic name Oxalaia is derived from the name of the African deity Oxalá, which was introduced into Brazil during the slavery period. The specific name quilombensis refers to the quilombo settlements like those on Cajual Island, which were founded by escaped slaves.[5]

Description

Oxalaia Size Chart
Tentative size estimate, with the animal in a swimming position

The holotype praemaxillae are together approximately 201 mm (7.9 in) long, with a preserved width of 115 mm (4.5 in) (maximal estimated original width is 126 mm (5.0 in)), and a height of 103 mm (4.1 in). Based on skeletal material from related spinosaurids, the skull of Oxalaia would have been an estimated 1.35 m (4 ft 5 in) long;[5] this is smaller than Spinosaurus's skull, which was approximated at 1.75 m (5 ft 9 in) long by Italian palaeontologist Cristiano Dal Sasso and colleagues in 2005.[16] Kellner and his team compared the Dal Sasso specimen (MSNM V4047) to Oxalaia's original snout in 2011; from this they estimated Oxalaia at 12 to 14 metres (39 to 46 ft) in length and 5 to 7 tonnes (5.5 to 7.7 short tons) in weight, making it the largest known theropod from Brazil,[5] the second largest being Pycnonemosaurus, which was estimated at 8.9 m (29 ft) by one study.[14][17]

The tip of the rostrum (snout) is enlarged and the rear-end constricted, forming the terminal rosette shape that distinguishes spinosaurids;[5] this form would have interlocked with the also-expanded front of the dentary (tooth-bearing bone of the mandible).[18] The rostrum of Oxalaia features broad, deep foramina (holes) that are possibly nutrient canals for blood vessels and nerves; it is also rounder in side view than that of Spinosaurus, whose upper jaw ends in a more acute downward angle as shown by specimens MSNM V4047 and MNHN SAM 124. The maxillae show a pair of elongated and thin processes extending forwards along the midline of the roof of the mouth; they are encased between the praemaxillae and border an elaborate, triangle-shaped pit at their front end. Similar processes are present in Suchomimus, Cristatusaurus, and MNHN SAM 124, although not as exposed.[5] These structures compose the animal's secondary palate.[5][19] The undersides of the praemaxillae are greatly ornamented in Oxalaia, in contrast to the smoother condition it has in other spinosaurids.[5]

Oxalaia quilombensis by PaleoGeek coloured
Hypothetical life restoration based on relatives

The praemaxillae have seven alveoli (tooth sockets) on each side, the same number found in Angaturama, Cristatusaurus, Suchomimus, and MNHN SAM 124 (referred to Spinosaurus); MSNM V4047, another upper jaw specimen from Spinosaurus, had only six. It cannot be confirmed whether this lower number of teeth is due to ontogeny; for that, a larger sample size is necessary. A large diastema (gap in tooth row) separates the third tooth socket from the fourth; this is observed in all other spinosaurids, being smaller in Suchomimus. Another diastema of nearly equal length is found between the fifth and sixth alveolus; this diastema is seen in MNHN SAM 124 and is much longer in MSNM V4047 but is absent from Suchomimus and Cristatusaurus. The maxilla fragment referred to Oxalaia (MN 6119-V) has two alveoli and a broken third one that includes a partial tooth. Like the praemaxilla, it had preserved nutrient canals. It also features a shallow dent in the middle, suggesting it was located near the external nares (bony nostrils). Small fragments inside some of the remaining alveoli show that unlike its Early Cretaceous relatives Suchomimus and Cristatusaurus, Oxalaia lacked serrations on its teeth. Apart from the single, functional tooth in each socket, there were two replacement teeth,[5] which according to Kellner are "a common feature in sharks or in some reptiles, but not in theropods".[15] A cross-section of the teeth showed the typical oval shape exhibited by spinosaurs rather than the lateral compression of other theropod teeth.[5]

The spinosaurid teeth reported from Laje do Coringa were classified into two primary morphotypes by Brazilian palaeontologist Manuel Medeiros in 2006. Both show typical spinosaurine dentition, though morphotype II has smoother tooth enamel than the first.[20] Oxalaia's teeth display a closer morphology to morphotype I while the second grouping of teeth represent either worn down morphotype I teeth or an undescribed spinosaurine from the Alcântara Formation.[5]

Classification

Spinosaurus skull en
Labeled skull diagram of the related Spinosaurus

The type elements of Oxalaia closely resemble those of specimens MSNM V4047 and MNHN SAM 124, both referred to Spinosaurus aegyptiacus, but Oxalaia can be differentiated from it and other spinosaurids by its autapomorphic (distinguishing) craniodental features, like its sculptured palatal part of the premaxillae, and the possession of two replacement teeth in each position.[5][19] More fragmentary spinosaurids such as Siamosaurus and "Sinopliosaurus" fusuiensis are based only on teeth, making them difficult to separate from other taxa. The habit of naming theropods from isolated teeth or tooth fragments has resulted in many invalid and synonymous genera; it has also occurred with spinosaurids and is compounded by the common lack of overlapping skeletal remains—a precondition of validly distinguishing taxa.[19][21]

In 2017, a phylogenetic analysis by the Brazilian palaeontologists Marcos Sales and Cesar Schultz concluded that Oxalaia was more closely related to African spinosaurines than to Brazilian spinosaurines like Angaturama, as indicated by a wider snout and the lack of a dorsal sagittal crest on the praemaxillae. The Brazilian genera Oxalaia and Angaturama were recovered as the two closest relatives of Spinosaurus, Oxalaia forming its sister taxon. Though fragmentary, the Brazilian material indicates that spinosaurines were more diverse than previously recognized. Spinosaurus differs from Oxalaia by its significantly more widely spaced tooth sockets, the presence of a slight narrowing between its third and fourth sockets, and the sharper slope of its snout. Oxalaia is currently assigned to the subfamily Spinosaurinae due to the morphology of its upper jaw and the absence of fine serrations on its teeth that typify baryonychines.[5][19] Below is a cladogram by Sales and Schultz, in which Oxalaia is grouped in the Spinosaurinae, as a closer relative to Spinosaurus than Angaturama.[19]

Spinosauridae

BaryonyxBaryonyx walkeri restoration

Cristatusaurus

SuchomimusSuchomimustenerensis (Flipped)

AngaturamaIrritator Life Reconstruction

Oxalaia

Spinosaurus Spinosaurus by Joschua Knüppe

Palaeoecology

Spinosaurid fossils palaeogeographic map
Generalised locations of spinosaurid fossil discoveries from the Albian-Cenomanian, 113 to 93.9 million years ago, marked on a map of that time span.

The Late Cretaceous deposits of the Alcântara Formation have been interpreted as a humid habitat of tropical forests dominated by conifers, ferns, and horsetails. These forests were surrounded by an arid-to-semi-arid landscape that was probably subjected to brief periods of heavy rainfall followed by lengthy dry periods.[1][22] A great abundance and variety of animal taxa, such as dinosaurs, pterosaurs, snakes, molluscs, crocodilians, notosuchids, and fish have been discovered in the formation. Aquatic taxa known from the deposits include the large coelacanth Mawsonia gigas; the ray Myliobatis; two sclerorhynchid sawfishes; as well as several bony fish, ray-finned fish, and lungfish species.[1][23] Dinosaur fossil remains suggest the presence of diplodocoids, basal titanosaurs, the giant theropod Carcharodontosaurus, a noasaurid closely related to Masiakasaurus, and a possible velociraptorine dromaeosaurid. Also, characteristic teeth and a single vertebral centrum were referred to Spinosaurus sp.[1]

Most of the flora and fauna discovered in the Alcântara Formation was also present in North Africa in the Kem Kem Beds of Morocco during the Cenomanian; with a few exceptions including Oxalaia quilombensis, Atlanticopristis equatorialis, Equinoxiodus alcantariensis, and Coringasuchus anisodontis. According to Medeiros and colleagues, the Laje do Coringa assemblage may also be linked to the contemporaneous Bahariya Formation in Egypt, which holds a distinct combination of key taxa constituting Spinosaurus aegyptiacus, Carcharodontosaurus saharicus, and Onchopristis numidus. This extreme similarity between the Cretaceous biota of Brazil with that of Africa is a result of their connection as parts of the supercontinent Gondwana (which comprised most landmasses of the modern southern hemisphere). This connection was broken by rifting and sea-floor spreading 130–110 million years ago. Afterwards, the transoceanic assemblages would have continued to evolve separately, contributing to small differences between taxa.[1][24] Machado stated that Cajual Island was still attached to the African continent during the Cenomanian.[6] Similarly, Medeiros and colleagues noted that the presence of an island chain or other lasting land connection during that time could explain the faunal similarities.[1]

Gavialis gangeticus, ZOO Praha 045 (Flipped and Cropped)
An Indian gharial, displaying the same interlocking rosette shape seen in spinosaurid snout tips

Spinosaurids likely spent most of their time near or in water and fed mostly on aquatic animals, avoiding direct competition with other large predators but being able to sustain themselves on terrestrial animals if necessary. Such behavior is observed in cases such as juvenile Iguanodon bones found in the stomach cavity of a Baryonyx fossil and an Irritator tooth embedded in pterosaur remains.[10][25] The conical, transversely oval-shaped teeth of Oxalaia and its nasal openings, that were retracted further back on the skull than in most theropods (likely to avoid water entering its nostrils while fishing) are characteristic of spinosaurids. Both features are useful adaptations for catching and feeding on fish.[5][10][18] The expanded, interlocking front jaws and piercing teeth of spinosaurs worked as an efficient fish trap, a trait also exhibited by the Indian gharial—the most piscivorous extant crocodilian.[18] Kellner compared the general appearance of spinosaurid skulls to those of alligators.[15]

References

  1. ^ a b c d e f g h 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. doi:10.1016/j.jsames.2014.04.002. ISSN 0895-9811.
  2. ^ "GSA Geologic Time Scale". The Geological Society of America. Archived from the original on 2019-01-20. Retrieved 2018-06-13.
  3. ^ Elias, Felipe; Bertini, Reinaldo; Alfredo Araújo Medeiros, Manuel (December 2007). "Pterosaur teeth from the Laje do Coringa, middle Cretaceous, São Luís-Grajaú basin, Maranhão state, Northern-Northeastern Brazil". Revista Brasileira de Geociências. 37 (4): 668–676. doi:10.25249/0375-7536.20073744760668676.
  4. ^ Catuneanu, O; Khalifa, M.A; Wanas, H.A (August 2006). "Sequence stratigraphy of the Lower Cenomanian Bahariya Formation, Bahariya Oasis, Western Desert, Egypt". Sedimentary Geology. 190 (1–4): 121–137. doi:10.1016/j.sedgeo.2006.05.010. ISSN 0037-0738.
  5. ^ a b c d e f g h i j k l m n o p q r s Kellner, Alexander W. A.; Azevedo, 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.
  6. ^ a b c Janeiro, Priscila Bessa, iG Rio de (March 2011). "Museu Nacional anuncia descoberta de maior dinossauro brasileiro – Ciência – iG". Último Segundo (in Portuguese). Retrieved 2018-06-12.
  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). Paleontologia: Cenários De Vida. 1. pp. 413–423. ISBN 9788571931848.
  8. ^ Martill, D. M.; Cruickshank, A. R. I.; Frey, E.; Small, P. G.; Clarke, M. (1996). "A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil". Journal of the Geological Society. 153: 5–8. doi:10.1144/gsjgs.153.1.0005.
  9. ^ Kellner, A. W. A.; Campos, D. A. (1996). "First Early Cretaceous dinosaur from Brazil with comments on Spinosauridae". N. Jb. Geol. Paläont. Abh. 199 (2): 151–166. doi:10.1127/njgpa/199/1996/151.
  10. ^ a b c Hone, David William Elliott; Holtz, Thomas Richard (June 2017). "A century of spinosaurs – a review and revision of the Spinosauridae with comments on their ecology". Acta Geologica Sinica – English Edition. 91 (3): 1120–1132. doi:10.1111/1755-6724.13328. ISSN 1000-9515.
  11. ^ Bertin, Tor (2010). "A catalogue of material and review of the Spinosauridae". PalArch's Journal of Vertebrate Palaeontology. 7 (4): 1–39.
  12. ^ Phillips, Dom (September 2018). "Brazil museum fire: 'incalculable' loss as 200-year-old Rio institution gutted". The Guardian. Retrieved 2018-09-03.
  13. ^ Lopes, Reinaldo José (September 2018). "Entenda a importância do acervo do Museu Nacional, destruído pelas chamas no RJ". Folha de S.Paulo (in Portuguese). Retrieved 2018-09-03.
  14. ^ a b c "Museu Nacional anuncia descoberta do maior dinossauro carnívoro do Brasil – Notícias – Ciência". Ciência (in Portuguese). Retrieved 2018-06-12.
  15. ^ a b c "Pictures: New Dinosaur, Crocodile Cousin Found in Brazil". National Geographic. March 2011. Retrieved 2018-06-12.
  16. ^ dal Sasso, C.; Maganuco, S.; Buffetaut, E.; Mendez, M.A. (2005). "New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities". Journal of Vertebrate Paleontology. 25 (4): 888–896. doi:10.1671/0272-4634(2005)025[0888:NIOTSO]2.0.CO;2. ISSN 0272-4634.
  17. ^ Grillo, O. N.; Delcourt, R. (2016). "Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king". Cretaceous Research. 69: 71–89. doi:10.1016/j.cretres.2016.09.001.
  18. ^ a b c Milner, Andrew; Kirkland, James (September 2007). "The case for fishing dinosaurs at the St. George Dinosaur Discovery Site at Johnson Farm". Utah Geological Survey Notes. 39: 1–3.
  19. ^ a b c d e Sales, M. A. F.; Schultz, C. L. (2017). "Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil". PLoS ONE. 12 (11): e0187070. doi:10.1371/journal.pone.0187070. PMC 5673194. PMID 29107966.
  20. ^ Medeiros, M. A. (2006). "Large theropod teeth from the Eocenomanian of northeastern Brazil and the occurrence of Spinosauridae". Revista Brasileira de Paleontologia. 9 (3): 333–338. doi:10.4072/rbp.2006.3.08.
  21. ^ Buffetaut, Eric; Ouaja, Mohamed (2002). "A new specimen of Spinosaurus (Dinosauria, Theropoda) from the Lower Cretaceous of Tunisia, with remarks on the evolutionary history of the Spinosauridae". Bulletin de la Société Géologique de France. 173 (5): 415–421. doi:10.2113/173.5.415.
  22. ^ Toledo, Carlos E. V.; Sousa, Eliane P. de; Medeiros, Manuel A. A.; Bertini, Reinaldo J. (December 2011). "A new genus of dipnoiformes from the Cretaceous of Brazil". Anais da Academia Brasileira de Ciências. 83 (4): 1181–1192. doi:10.1590/S0001-37652011000400006. ISSN 0001-3765.
  23. ^ 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.
  24. ^ 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. doi:10.1016/j.jsames.2014.10.005. ISSN 0895-9811.
  25. ^ Amiot, R.; Buffetaut, E.; Lécuyer, C.; Wang, X.; Boudad, L.; Ding, Z.; Fourel, F.; Hutt, S.; Martineau, F.; Medeiros, A.; Mo, J.; Simon, L.; Suteethorn, V.; Sweetman, S.; Tong, H.; Zhang, F.; Zhou, Z. (2010). "Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods". Geology. 38 (2): 139–142. Bibcode:2010Geo....38..139A. doi:10.1130/G30402.1.

External links

  • Data related to Oxalaia at Wikispecies
2011 in archosaur paleontology

The year 2011 in Archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago. The year 2011 in paleontology included various significant developments regarding archosaurs.

This article records new taxa of fossil archosaurs of every kind that have been described during the year 2011, as well as other significant discoveries and events related to paleontology of archosaurs that occurred in the year 2011.

Alcântara Formation

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

Alexander Kellner

Alexander Wilhelm Armin Kellner (born September 26, 1961) is a Brazilian geologist and paleontologist who is a leading expert in the field of studying pterosaurs. His research has focused mainly on fossil reptiles from the Cretaceous Period, including extinct dinosaurs and crocodylomorphs.Kellner has over 500 publications to his name, has published more than 160 primary studies and two science books. He has participated in paleontological expeditions to many locations including Brazil, Chile, Iran, the United States, Argentina, China, and Antarctica.

His scientific achievements include the description of more than thirty species. For his work he has received several honors and prizes, including the TWAS Prize for Earth Sciences from The World Academy of Sciences and admission to the National Order of Scientific Merit (class Comendador), one Brazil's most prestigious awards.

Atlanticopristis

Atlanticopristis (meaning "Atlantic saw") is an extinct genus of sclerorhynchid sawfish 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 Portuguese 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.

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, and also such plants as conifers and ferns. The finds include the remains of the largest carnivorous dinosaur in Brazil. Traces of the maxillary and nostril of the specimen were found. Known as Oxalaia quilombensis, the species is part of the family of dinosaurs known as Spinosauridae, with elongated skulls and spines along the back.

The presence of fossils also present in Africa proves that the continents were once united, forming Gondwana. The "Lage of the Joker", where the fossils are found, is up to 2 meters below the water at high tide, so it can only be visited for only a few hours a day.

Currently, the island of Cajual is home to a small community of quilombolas.

Cenomanian

The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.

As a unit of geologic time measure, the Cenomanian age spans the time between 100.5 ± 0.9 Ma and 93.9 ± 0.8 Ma (million years ago). In the geologic timescale it is preceded by the Albian and is followed by the Turonian. The Upper Cenomanian starts approximately at 95 M.a.

The Cenomanian is coeval with the Woodbinian of the regional timescale of the Gulf of Mexico and the early part of the Eaglefordian of the regional timescale of the East Coast of the United States.

At the end of the Cenomanian an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli Event", that is associated with a minor extinction event for marine species.

Cristatusaurus

Cristatusaurus is a genus of theropod dinosaur that lived during the Early Cretaceous Period of what is now Niger, 112 million years ago. It was a baryonychine member of the Spinosauridae, a group of large bipedal carnivores with well-built forelimbs and elongated, crocodile-like skulls. The type species Cristatusaurus lapparenti was named in 1998 by scientists Philippe Taquet and Dale Russell, on the basis of jaw bones and some vertebrae. Two claw fossils were also later assigned to Cristatusaurus. The animal's generic name, which means "crested reptile", alludes to a sagittal crest on top of its snout; while the specific name is in honor of the French paleontologist Albert-Félix de Lapparent. Cristatusaurus is known from the Albian to Aptian Erlhaz Formation, where it would have coexisted with sauropod and iguanodontian dinosaurs, other theropods, and various crocodylomorphs.

Originally proposed to be an indeterminate species of Baryonyx, the identity of Cristatusaurus has been subject to debate, in part due to the fragmentary nature of its fossils. Some argue that it is probably the same dinosaur as Suchomimus, which has also been found in Niger, in the same sediment layers. In that case the genus Cristatusaurus would have priority, since it was named two months earlier. Others have concluded, however, that Cristatusaurus is a nomen dubium, considering it indistinguishable from both Suchomimus and Baryonyx. Some distinctions between the fossils of Cristatusaurus and Suchomimus have been pointed out, but it is uncertain whether these differences separate the two genera or if they are due to ontogeny (changes in an organism during growth).

Dinosaur size

Size has been one of the most interesting aspects of dinosaur science to the general public and to scientists. Dinosaurs show some of the most extreme variations in size of any land animal group, ranging from the tiny hummingbirds, which can weigh as little as three grams, to the extinct titanosaurs, which could weigh as much as 90 tonnes (89 long tons; 99 short tons).Scientists will probably never be certain of the largest and smallest dinosaurs to have ever existed. This is because only a tiny fraction of animals ever fossilize, and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork. Weight estimates for dinosaurs are much more variable than length estimates, because estimating length for extinct animals is much more easily done from a skeleton than estimating weight. Estimating weight is most easily done with the laser scan skeleton technique that puts a "virtual" skin over it, but even this is only an estimate.Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the 100- to 1,000-kilogram (220 to 2,200 lb) category when sorted by estimated weight into categories based on order of magnitude, whereas recent predatory carnivoran mammals peak in the 10- to 100-kilogram (22 to 220 lb) category. The mode of Mesozoic dinosaur body masses is between one and ten metric tonnes. This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kg (4.4 to 11.0 lb).

Ichthyovenator

Ichthyovenator (meaning "fish hunter") is a genus of spinosaurid theropod dinosaur that lived during the Early Cretaceous of what is now Laos, likely from the Aptian stage (113–125 million years ago). Ichthyovenator is known from fossils collected in the Grès supérieurs Formation. Like other members of its family, it had elongated neural spines forming a sail on its back, although Ichthyovenator's was unusual due to its particular wave-like curvature and being split in two over the hips. Ichthyovenator was initially thought to belong to the Baryonychinae subfamily, but more recent analyses place it in the Spinosaurinae.

Irritator

Irritator is a genus of spinosaurid theropod dinosaur that lived in what is now Brazil during the Albian stage of the Early Cretaceous Period, about 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 illegally 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 an homage to the fictional character Professor Challenger from Arthur Conan Doyle's novels.

Many paleontologists regard Angaturama limai—known from a snout tip that was described later in 1996—as a potential junior synonym of Irritator. Both animals hail from the same stratigraphic units of the Araripe Basin. It was also previously proposed that Irritator and Angaturama's skull parts belonged to the same specimen. Although this has been cast into doubt, more overlapping fossil material is needed to confirm whether they are the same animal or not. Other spinosaurid skeletal material, some of which could belong to Irritator or Angaturama, was retrieved from the Romualdo Formation, allowing for a replica skeleton to be made and mounted for display at the National Museum of Rio de Janeiro in 2009.

Estimated at between 6 and 8 meters (20 and 26 ft) in length, Irritator weighed around 1 tonne (1.1 short tons), making it one of the smallest spinosaurids known. Its long, shallow and slender snout was lined with straight and unserrated conical teeth. Lengthwise atop the head ran a thin sagittal crest, to which powerful neck muscles were likely anchored. The nostrils were positioned far back from the tip of the snout, and a rigid secondary palate on the roof of the mouth would have strengthened the jaw when feeding. Belonging to a subadult, Irritator challengeri's holotype remains the most completely preserved spinosaurid skull yet found. The Angaturama snout tip expanded to the sides in a rosette-like shape, bearing long teeth and an unusually tall crest. One possible skeleton indicates it, like other spinosaurids, had enlarged first-finger claws and a sail running down its back.

Irritator had been mistaken initially for a pterosaur, and later a maniraptoran dinosaur. In 1996, the animal was identified as a spinosaurid theropod. The holotype skull was thoroughly prepared before being redescribed in 2002, confirming this classification. Both Irritator and Angaturama belong to the Spinosaurinae subfamily. A generalist diet—like that of today's crocodilians—has been suggested; Irritator might have preyed mainly on fish and any other small prey animals it could catch. Fossil evidence is known of an individual that ate a pterosaur, either from hunting or scavenging it. Irritator may have had semiaquatic habits, and inhabited the tropical environment of a coastal lagoon surrounded by dry regions. It coexisted with other carnivorous theropods as well as turtles, crocodyliforms, and a large number of pterosaur and fish species.

List of South American dinosaurs

This is a list of dinosaurs whose remains have been recovered from South America.

List of dinosaur genera

This list of dinosaurs is a comprehensive listing of all genera that have ever been included in the superorder Dinosauria, excluding class Aves (birds, both living and those known only from fossils) and purely vernacular terms.

The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered dinosaurs. Many listed names have been reclassified as everything from birds to crocodilians to petrified wood. The list contains 1559 names, of which approximately 1192 are considered either valid dinosaur genera or nomina dubia.

Spinosauridae

Spinosauridae (meaning "spined lizards") is a family of megalosauroidean theropod dinosaurs. The genus Spinosaurus, from which the family, subfamily, and tribe borrow their names, is the longest terrestrial predator known from the fossil record, and likely reached lengths of 15 m (49 ft). Most spinosaurids lived during the Cretaceous Period, with possible origins in the Late Jurassic, and fossils of them have been recovered worldwide, including in Africa, Europe, South America, Asia, and Australia, although none have been formally named from the latter continent. Spinosaur remains have generally been attributed to the Early to Mid Cretaceous, with the exception of the Ostafrikasaurus from the Late Jurassic.

Spinosaurids were large bipedal carnivores with elongated, crocodile-like skulls lined with conical teeth bearing little to no serrations, and small crests on top of their heads. The teeth in the front end of their lower jaws fanned out into a spoon-shaped structure similar to a rosette, which gave the animal a characteristic look. Their shoulders were robust, prominent and bore stocky forelimbs with giant "hooked" claws on the first finger of their hands. Many genera had unusually tall neural spines on their vertebrae, which supported sails or humps of skin or fat tissue.

Direct fossil evidence and anatomical adaptations indicate that spinosaurids were at least partly piscivorous, with additional fossil finds indicating they also hunted pterosaurs and small to medium-sized dinosaurs. Osteological analyses have suggested a semiaquatic lifestyle for some members of this clade.

Spinosaurus

Spinosaurus (meaning "spine lizard") is a genus of theropod dinosaur that lived in what now is North Africa, during the upper Albian to upper Turonian stages of the Cretaceous period, about 112 to 93.5 million years ago. This genus was known first from Egyptian remains discovered in 1912 and described by German paleontologist Ernst Stromer in 1915. The original remains were destroyed in World War II, but additional material has come 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.

Spinosaurus was among the largest of all known carnivorous dinosaurs, nearly as large as or even larger than Tyrannosaurus, Giganotosaurus and Carcharodontosaurus. Estimates published in 2005, 2007, and 2008 suggested that it was between 12.6–18 metres (41–59 ft) in length and 7 to 20.9 tonnes (7.7 to 23.0 short tons) in weight. New estimates published in 2014 and 2018 based on a more complete specimen, supported the earlier research, finding that Spinosaurus could reach lengths of 15–16 m (49–52 ft). The latest estimates suggest a weight of 6.4–7.5 tonnes (7.1–8.3 short tons). The skull of Spinosaurus was long and narrow, similar to that of a modern crocodilian. Spinosaurus is known to have eaten fish, and most scientists believe that it hunted both terrestrial and aquatic prey; evidence suggests that it lived both on land and in water as a modern crocodilian does. The distinctive spines of Spinosaurus, which were long extensions of the vertebrae, grew to at least 1.65 meters (5.4 ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that the spines were covered in fat and formed a hump. Multiple functions have been put forward for this structure, including thermoregulation and display.

Piatnitzkysauridae
Megalosauria

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