Oxalaia

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Oxalaia
Temporal range:
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 Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Spinosauridae
Genus: †Oxalaia
Kellner et al., 2011
Species:
†O. quilombensis
Binomial name
†Oxalaia quilombensis
Kellner et al., 2011
Synonyms
  • Oxalaia quilimboensis Arden et al., 2018 (
    lapsus calami
    )

Oxalaia (in reference to the African deity

junior synonym
of this taxon.

Although Oxalaia is known only from two partial skull bones, Kellner and colleagues found that its teeth and

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
.

Discovery and naming

spinosaurine fossil specimens in the Araripe and São Luís-Grajaú Basins marked. From top to bottom: Oxalaia, Irritator
, and Angaturama.

Oxalaia stems from 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]

Silhouette of Oxalaia's head with the fossil jaw and snout fragments in place
Diagram illustrating known jaw material in place

Oxalaia is one of three

Sigilmassasaurus brevicollis.[1] American palaeontologist Mickey Mortimer informally noted that these may instead belong to Oxalaia.[14]

The discoveries of Oxalaia and of the Late Cretaceous reptiles

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]

Specimen UFMA 1.10.240, a distal caudal vertebra which was discovered in the

Alcantara Formation of Brazil was assigned to Sigilmassasaurus in 2002.[17]

Description

Diagram with the silhouettes of a swimming Oxalaia and a scuba diver in side view, the dinosaur is roughly over seven times longer than the human
Tentative size estimate, with the animal in a swimming position

The holotype premaxillae are together approximately 201 millimetres (7.9 inches) 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 metres (4.4 feet) 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.[18] 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 m (39 to 46 ft) in length and 5 to 7 tonnes (5.5 to 7.7 short tons; 4.9 to 6.9 long 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.[15][19]

The tip of the

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 premaxillae 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][21] The undersides of the premaxillae are greatly ornamented in Oxalaia, in contrast to the smoother condition it has in other spinosaurids.[5]

Speculative life restoration of Oxalaia depicted as similar to Spinosaurus, with half its body underwater while in a swimming position
Hypothetical life restoration based on relatives

The premaxillae have seven

replacement teeth,[5] which according to Kellner are "a common feature in sharks or in some reptiles, but not in theropods".[16] 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.[22] 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

spinosaurids
(Oxalaia in green, third from left) compared with a human

The type elements of Oxalaia closely resemble those of specimens MSNM V4047 and MNHN SAM 124, both referred to Spinosaurus aegyptiacus. Kellner and colleagues differentiated Oxalaia from it and other spinosaurids by its

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.[21][23]

Skull diagram of Spinosaurus, with the different bones labeled and color coded
Labeled skull diagram of the related Spinosaurus

In 2017, a

baryonychines.[5][21] Below is a cladogram by Sales and Schultz, in which Oxalaia is grouped in the Spinosaurinae, as a closer relative to Spinosaurus than Angaturama.[21]

Spinosauridae

In 2020, a paper by Robert Smyth and colleagues assessing spinosaurines from the

individual variation. The authors thus considered the species a junior synonym of Spinosaurus aegyptiacus. If supported by future studies, this would imply Spinosaurus aegyptiacus had a wider distribution and support a faunal exchange scenario between South America and Africa during the Cenomanian when there was little separation of South America and Africa by water, which allowed Spinosaurus aegyptiacus to traverse the short distance of the sea into South America.[24]

Palaeoecology

Locations of spinosaurid fossil discoveries marked with white circles on a map of Earth during the Albian to the Cenomanian of the Cretaceous Period
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

titanosaurs, a giant Carcharodontosaurid sp., a noasaurid closely related to Masiakasaurus, and a dromaeosaurid. Also, characteristic teeth and a vertebral centra were referred to Spinosaurus sp.[1][27]

Most of the flora and fauna discovered in the Alcântara Formation was also present in North Africa in the

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][28] 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]

Indian gharial, displaying the same interlocking rosette
shape seen in spinosaurid snout tips

As a spinosaur, Oxalaia would have had large, robust forelimbs; relatively short hindlimbs; elongated

piscivorous extant crocodilian.[20] Kellner compared the general appearance of spinosaurid skulls to those of alligators.[16]

References

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  2. ^ "GSA Geologic Time Scale". The Geological Society of America. Archived from the original on 2019-01-20. Retrieved 2018-06-13.
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    PMID 21437377
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  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 Brazilian Portuguese). Retrieved 2018-06-12.{{cite news}}: CS1 maint: multiple names: authors list (link)
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  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 Brazilian Portuguese). Retrieved 2018-09-03.
  14. ^ Mortimer, M. "Megalosauroidea". theropoddatabase.com. Retrieved 2018-11-06.
  15. ^ a b c "Museu Nacional anuncia descoberta do maior dinossauro carnívoro do Brasil – Notícias – Ciência". Ciência (in Brazilian Portuguese). Retrieved 2018-06-12.
  16. ^ a b c "Pictures: New Dinosaur, Crocodile Cousin Found in Brazil". National Geographic. March 2011. Archived from the original on March 31, 2011. Retrieved 2018-06-12.
  17. ^ Medeiros and Schultz, (2002). A fauna dinossauriana da Laje do Coringa, Cretáceo médio do Nordeste do Brasil. Arquivos do Museu Nacional. 60(3), 155-162.
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  19. doi:10.1016/j.cretres.2016.09.001
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  20. ^ 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.
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  22. doi:10.4072/rbp.2006.3.08
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  26. doi:10.4072/rbp.2008.3.07
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  29. S2CID 134735938. Archived
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  30. doi:10.1130/G30402.1
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External links

  • Data related to Oxalaia at Wikispecies

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