Oxalaia

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 fragmentary fossil specimens, also including fossils from the Itapecuru Formation. The remains of Oxalaia were described by Brazilian palaeontologist Alexander Kellner and colleagues, who named the species Oxalaia quilombensis, referencing the Brazilian quilombo settlements.

Oxalaia quilombensis is the eighth officially named theropod species from Brazil and the largest carnivorous dinosaur discovered there. Some studies suggest it may be closely related to the African genus Spinosaurus, but others believe it is a distinct genus.

Although Oxalaia is known only from two partial skull bones, scientists found unique features in its teeth and skull. These traits suggest it had a partly piscivorous (fish-eating) lifestyle, similar to modern crocodilians. It lived in a tropical, forested area surrounded by arid land, which was connected to North Africa when the continents were part of the supercontinent Gondwana. Evidence shows that spinosaurids like Oxalaia may have also eaten small dinosaurs and pterosaurs.

Discovery and naming

Oxalaia was found in northeastern Brazil, in rocks from the Late Cretaceous period, about 100.5 to 93.9 million years ago. The fossils were discovered in 1999 on Cajual Island. Palaeontologist Elaine Machado was surprised by the well-preserved fossil and described the discovery as accidental. Usually, fossils from this area are fragmented because of erosion, but Oxalaia was an exception.

Oxalaia is one of three spinosaurid dinosaurs found in Brazil. The first fossils of Oxalaia were described in 2011 by Brazilian palaeontologists. The name Oxalaia comes from Oxalá, an African deity brought to Brazil during slavery, and the specific name quilombensis refers to the quilombo settlements founded by escaped slaves on Cajual Island.

Description

The fossils of Oxalaia show that it had a long skull, estimated to be about 1.35 metres (4.4 feet) long. This makes it smaller than its relative, Spinosaurus, but still one of the largest meat-eating dinosaurs found in Brazil. The front of its snout was wide and formed a special shape, helping it fit together with its lower jaw.

Oxalaia had special bones in its upper jaw with holes that may have held blood vessels and nerves. Its teeth were different from older spinosaurids, lacking the jagged edges that others had. Instead, Oxalaia had two extra teeth growing in each socket, a feature more common in sharks than in other meat-eating dinosaurs.

Classification

The fossils of Oxalaia share similarities with another spinosaurid dinosaur called Spinosaurus aegyptiacus, but scientists have found enough differences to classify it as a separate species. These differences include unique features in its skull, such as a special shape on the upper jaw and the presence of extra teeth.

Studies over the years have tried to understand where Oxalaia fits among its relatives. Some suggest it is closely related to African spinosaurids, while others debate whether it should be considered the same species as Spinosaurus aegyptiacus. However, recent research supports that Oxalaia is a distinct species, with its own unique skull characteristics that set it apart from other spinosaurids.

Palaeoecology

The Late Cretaceous deposits of the Alcântara Formation were a humid habitat of tropical forests with conifers, ferns, and horsetails. These forests were surrounded by an arid-to-semi-arid landscape. Many animals lived there, including dinosaurs, pterosaurs, snakes, molluscs, crocodilians, notosuchids, and fish.

As a spinosaur, Oxalaia would have had large forelimbs, short hindlimbs, and a ridge or sail on its back. Spinosaurids probably spent time near or in water, eating mostly aquatic animals. They could also eat land animals if needed. Oxalaia’s teeth and skull were well-suited for catching and eating fish, similar to modern Indian gharial and alligators.