Oxalaia, named after the African deity Oxalá, is a spinosaurid dinosaur genus that roamed what is today the Northeast Region of Brazil during the Cenomanian stage within the Late Cretaceous period, spanning from approximately 100.5 to 93.9 million years ago. This dinosaur is represented by a rather scant fossil record, discovered in 1999 on Cajual Island, within the rock layers of the Alcântara Formation. These formations are notable for their wealth of fragmentary, isolated fossil specimens. The formal description of Oxalaia took place in 2011.

The entirety of our knowledge about Oxalaia is rooted in just two partial skull bones. However, careful examination of these remains by researchers uncovered several distinct features, setting it apart from other spinosaurids and theropods. These distinguishing features included having two replacement teeth within each socket and the presence of a remarkably sculptured secondary palate. The rostrum, or snout, displayed an enlarged tip, with a narrowed rear end forming the characteristic terminal rosette shape that is a hallmark of spinosaurids.

The habitat of Oxalaia was tropical, characterized by dense forests and situated in the midst of a surrounding arid landscape. This environment hosted a rich diversity of lifeforms, many of which also existed in Middle-Cretaceous North Africa. This ecological similarity is explained by the geological connection of South America and Africa as integral components of the supercontinent Gondwana.

Being a spinosaurid, Oxalaia's cranial structure and dental features are indicative of a predominantly piscivorous, or fish-eating, lifestyle, akin to modern crocodilians. Fossil evidence strongly suggests that spinosaurids diversified their diet to encompass other creatures like small dinosaurs and pterosaurs.

Estimates regarding Oxalaia's size place it in the range of 12 to 14 meters (39 to 46 feet) in length and a weight of approximately 5 to 7 tonnes (5.5 to 7.7 short tons; 4.9 to 6.9 long tons), thus earning it the distinction of being the largest known theropod dinosaur discovered in Brazil.