Oxalaia (in reference to the African deity Oxalá) is a genus of spinosaurid 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 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. One study suggested that this taxon is a junior synonym of the closely related African genus Spinosaurus, but some subsequent studies consider the genus to be diagnostic. 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.
Discovery and naming
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. 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. These sediments were deposited under marine and fluvial conditions similar to those of the Bahariya Formation in Egypt, where Spinosaurus remains have been found. In 1999, fossils of Oxalaia were recovered from the Laje do Coringa. 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". 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. 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.
Oxalaia is one of three spinosaurid dinosaurs 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. 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. 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 premaxillae (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. In 2018, a fire engulfed the palace housing the museum, possibly destroying Oxalaia's specimens, along with various other fossils found in Brazil. It was noted by paleontologist Rubi Pêgas in 2025 that the badly damaged remains of Oxalaia were recovered, and the publication for the recovered items is in preparation. Besides the partial skull bones, numerous spinosaurid teeth had earlier been reported from the Laje do Coringa site. Additionally, two distal caudal vertebra (specimens UFMA 1.10.229 and UFMA 1.10.240) discovered in the Alcantara Formation of Brazil were assigned to Sigilmassasaurus in 2002. However, other researchers noted that these specimens are indeterminate spinosaurids, most likely belonging to Oxalaia considering the geographical and geological context. 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. 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. 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. 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.
Description
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