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Oxalaia

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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 e
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

Oxalaia was a large predatory dinosaur. It lived during the Upper Cretaceous of what is now Brazil, sometime between 100.5 to 93.9 million years ago. Oxalaia is known only from two bones of the skull, which were found in 1999. The animal was named in 2011 by Brazilian palaeontologists.

It was a member of the Spinosauridae family, a group of crocodile-like theropod dinosaurs. Like other spinosaurids, Oxalaia had a long snout with jaws and teeth shaped to feed on fish. Oxalaia's habitat was tropical, with large forests surrounded by dry deserts. Oxalaia shared this environment with many other animals, most of which are also known from the Cretaceous of Africa.

Discovery and naming[change | change source]

Diagram showing the known skull fossils in place

Fossils of Oxalaia were found in the Northeast Region of Brazil in 1999. The region they were found in always gets covered up by the sea and eroded, so they were almost lost.[1] Multiple fossil teeth were also found at the same site.[2]

The full name of the dinosaur is Oxalaia quilombensis. The animal was named by Brazilian palaeontologists Alexander Kellner, Elaine Machado, Sergio Azevedo, Deise Henriques, and Luciana Carvalho. The first part of the dinosaur's name (the genus) comes from an African god. The second part of the name (the species) comes from the quilombos, a group of Brazilian towns.[1]

In 2011, the discovery of Oxalaia was presented at the Brazilian Academy of Sciences.[3] Machado said that people are interested in spinosaurids: because of how different they are from other carnivorous dinosaurs, and because of their introduction to the public in the Jurassic Park franchise.[4]

Only two pieces of bone are known from Oxalaia. The first is the front of its snout, called the premaxilla bone. The second is a piece of its left maxilla, or upper jaw bone. The specimens were put on display in the National Museum of Brazil in 2011.[1] A large fire broke out at the museum in 2018, possibly destroying Oxalaia's fossils.[5][6]

Oxalaia is the third spinosaurid named from Brazil so far. The other two are Irritator and Angaturama (which might be the same animal as Irritator). These two animals are known from another part of Brazil, and lived nine to six million years before Oxalaia.[1][7][8]

Description[change | change source]

Size compared to a human

To estimate its size, Oxalaia's skull bones were compared with those of its close relative, Spinosaurus. Oxalaia was probably 12 to 14 metres (39 to 46 feet) long, and likely weighed 5 to 7 tonnes (4.9 to 6.9 long tons; 5.5 to 7.7 short tons). This makes it the largest known carnivorous dinosaur from Brazil.[1]

The tip of Oxalaia's snout, called the premaxilla, was 201 millimetres (7.9 inches) long. Oxalaia's complete skull was probably 1.35 metres (4 feet 5 inches) long.[1] This is shorter than the skull of Spinosaurus, which was 1.75 metres (69 in) long.[9]

What Oxalaia might have looked like, based on its relatives

The front of Oxalaia's upper jaw was spoon-shaped, or larger at its front end than at its rear end. The bottom of the snout tip was curved inwards. This shape would have connected with the lower jaw, or mandible, which was also spoon-shaped.[1] The roof of Oxalaia's mouth had a very complex and bony surface, called a secondary palate. This structure made the upper jaw more sturdy, so it would bend less when feeding.[1][10][7] The fossil snout preserves broad and deep holes. These probably contained blood vessels and nerves.[1]

The snout of Oxalaia had seven tooth sockets on each side. It had one tooth in each socket, and there were two teeth underneath to replace it if it fell out.[1] This feature is common in sharks, but not in most theropod dinosaurs.[11] Oxalaia's teeth were also oval in cross section, instead of flattened somewhat sideways like in most theropods.[1]

Classification[change | change source]

Labeled skull diagram of the related Spinosaurus

Oxalaia is more closely related to the African than Brazilian members of its family. Oxalaia, Irritator, Angaturama, Ichthyovenator, and Spinosaurus are the only five dinosaurs from their clade that don't have knife-like (or serrated) teeth. This places them in their own subfamily, called the Spinosaurinae.[1][10][12]

Oxalaia can be separated from Spinosaurus by differences between their jaw bones. For example: Oxalaia had a rounder snout, and more closely spaced teeth than Spinosaurus. Oxalaia's two replacement teeth per socket, and less smooth secondary palate, also make it unique among the other known spinosaurs.[1]

The cladogram below is from a study by Marcos Sales and Cesar Schultz. It shows Oxalaia's relationship with other spinosaurids:[10]

Spinosauridae

BaryonyxBaryonyx walkeri restoration.jpg



Cristatusaurus



SuchomimusSuchomimustenerensis (Flipped).png




AngaturamaIrritator Life Reconstruction.jpg




Oxalaia



Spinosaurus Spinosaurus by Joschua Knüppe.png






Palaeobiology[change | change source]

Diet and feeding[change | change source]

An Indian gharial, showing the same interlocking shape of spinosaurid snout tips

Spinosaurids likely spent most of their time near or in water, feeding mostly on aquatic animals like fish. This way, they would avoid competing with other large predatory dinosaurs. Fossil evidence shows that spinosaurs sometimes also ate pterosaurs and small dinosaurs.[13][14]

The cone-shaped teeth of Oxalaia were built for impaling prey, instead of cutting flesh like those of most theropod dinosaurs. Oxalaia's nostrils were placed far back on the head. This was probably to avoid water getting inside its nostrils when fishing. Both of these features were unique to spinosaurid dinosaurs. Because they were useful for catching and feeding on fish.[1][13][15]

The spoon-shaped front jaws and piercing teeth of spinosaurs worked as an efficient fish trap. This trait is also seen in the Indian gharial—the most fish-eating of the living crocodilians.[15]

Habitat[change | change source]

Map of Earth, 113 to 93.9 million years ago. The white dots are spinosaurid fossils dated to that time period

Oxalaia is known from the Alcântara Formation, a geological formation in northeastern Brazil. This formation dates to the Upper Cretaceous Period, sometime between 100.5 to 93.9 million years ago. Back then, the environment of the formation had a wet climate. There were large tropical forests made of plants like conifer trees, ferns, and horsetails. These forests were surrounded by an arid, or dry, landscape.[16][17]

Oxalaia shared this habitat with many different kinds of animals. Other dinosaurs from the formation included giant carnivores like Carcharodontosaurus, and perhaps Spinosaurus. Smaller predators lived there too, such as dromaeosaurids, and an animal very similar to Masiakasaurus. There were also large sauropods, a group of herbivorous (plant-eating) dinosaurs. Fish from the formation included bony fish, ray-finned fish, and lungfish. There were also giant coelacanths and sawfishes. Besides dinosaurs, there were other reptiles, like pterosaurs and crocodilians. Fossils of snakes and molluscs have also been found.[16]

The fauna from the Upper Cretaceous of Brazil is very similar to that of Morocco and Egypt during the same time period. This is because South America and Africa used to be connected, in a giant supercontinent called Gondwana.[16][18]

References[change | change source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 Kellner, Alexander W.A. et al (2011). "A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil". Anais da Academia Brasileira de Ciências 83 (1): 99–108. doi:10.1590/S0001-37652011000100006. ISSN 0001-3765. http://www.scielo.br/pdf/aabc/v83n1/v83n1a06.pdf. 
  2. Medeiros, M.A. (2006). "Large theropod teeth from the Eocenomanian of northeastern Brazil and the occurrence of Spinosauridae". Revista Brasileira de Paleontologia 9: 333–338. doi:10.4072/rbp.2006.3.08. 
  3. "Pictures: New Dinosaur, Crocodile Cousin Found in Brazil". National Geographic. March 2011. Retrieved 2018-06-12.
  4. "Museu Nacional anuncia descoberta do maior dinossauro carnívoro do Brasil – Notícias". Ciência (in Portuguese). Retrieved 2018-06-12.
  5. Phillips, Dom (September 2018). "Brazil museum fire: 'incalculable' loss as 200-year-old Rio institution gutted". The Guardian. Retrieved 2018-09-03.
  6. 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.
  7. 7.0 7.1 Sues, Hans-Dieter; Frey, Eberhard; Martill, David; Scott, Diane (2002). "Irritator challengeri, a Spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil". Journal of Vertebrate Paleontology 22 (3): 535–547. doi:10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2. https://www.researchgate.net/publication/254314432. 
  8. 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. 
  9. 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. http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1671%2F0272-4634%282005%29025%5B0888%3ANIOTSO%5D2.0.CO%3B2. 
  10. 10.0 10.1 10.2 Sales, Marcos A. F.; Schultz, Cesar L. (2017). "Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil". PLOS ONE 12 (11): e0187070. doi:10.1371/journal.pone.0187070. ISSN 1932-6203. PMC 5673194. PMID 29107966. 
  11. "Pictures: New Dinosaur, Crocodile Cousin Found in Brazil". National Geographic. March 2011. Retrieved 2018-06-12.
  12. Allain, Ronan (2014). "New material of the theropod Ichthyovenator from Ban Kalum type locality (Laos): Implications for the synonymy of Spinosaurus and Sigilmassasaurus and the phylogeny of Spinosauridae". Journal of Vertebrate Paleontology Programs and Abstracts. http://vertpaleo.org/GlobalPDFS/SVP-2014-Program-and-Abstract-Book-9-18-2014.aspx. 
  13. 13.0 13.1 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. https://onlinelibrary.wiley.com/doi/abs/10.1111/1755-6724.13328. 
  14. Amiot, R.; Buffetaut, E.; Lécuyer, C.; Wang, X.; Boudad, L.; Ding, Z.; Fourel, F.; Hutt, S. et al. (2010). "Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods". Geology 38 (2): 139–142. doi:10.1130/G30402.1. 
  15. 15.0 15.1 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. https://www.researchgate.net/publication/285906225_The_case_for_fishing_dinosaurs_at_the_St_George_Dinosaur_Discovery_Site_at_Johnson_Farm. 
  16. 16.0 16.1 16.2 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. https://www.sciencedirect.com/science/article/pii/S0895981114000364. 
  17. 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. http://www.scielo.br/scielo.php?script=sci_abstract&pid=S0001-37652011000400006&lng=en&nrm=iso&tlng=en. 
  18. 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. https://www.sciencedirect.com/science/article/pii/S0895981114001424. 

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