Description and Classification

Oxalaia is recognized as a member of the Spinosauridae family, a group of carnivorous dinosaurs known for their long, crocodile-like snouts and conical teeth, well-suited for catching fish. Based on the size of its snout fragments, paleontologists estimate that Oxalaia was a very large predator, potentially reaching lengths of 12 to 14 meters (about 39 to 46 feet) and weighing between 5 to 7 metric tons (around 5.5 to 7.7 short tons). This would make it one of the largest theropods ever discovered in South America, rivaling even some members of the carcharodontosaurid family from the same continent.

The classification of Oxalaia places it within the subfamily Spinosaurinae, alongside its close relative Spinosaurus from North Africa. This is based on features like the morphology of its premaxillary teeth (the teeth at the very tip of the snout) and the arrangement of openings for nerves and blood vessels on the snout. However, knowledge of Oxalaia is limited because it is only known from a fused pair of premaxillae (the bones forming the tip of the upper jaw) and a fragment of a maxilla (the main bone of the upper jaw). These fragments, though incomplete, provide important clues about its appearance and relationships to other spinosaurids like Baryonyx and Suchomimus.

Distinguishing Features

Despite being known from limited fossil material, Oxalaia possesses several features that help distinguish it from other spinosaurids:

• Its snout tip (formed by the premaxillae) is notably wider and more rounded compared to many other spinosaurids, though similar in some respects to certain specimens of Spinosaurus.
• The first two teeth in its premaxilla were relatively unserrated, meaning they lacked the tiny, knife-like ridges common on the teeth of many carnivorous dinosaurs.
• It has a unique arrangement of foramina (small openings) on the side of the snout tip, which likely housed nerves and blood vessels associated with sensory organs for detecting prey in water.
• The premaxillae were completely fused, with no visible seam between them, even on the palate (roof of the mouth).

Paleoenvironment and Diet

Oxalaia lived in a lush, tropical coastal environment during the Late Cretaceous. The Alcântara Formation, where its fossils were discovered, represents an ancient system of river deltas, mangrove swamps, and shallow marine areas. The climate was warm and humid. This environment supported a diverse ecosystem, including other dinosaurs such as rebbachisaurid sauropods (long-necked plant-eaters) and carcharodontosaurid theropods (large meat-eaters), as well as various species of crocodiles, turtles, pterosaurs (flying reptiles), and abundant fish.

Like other spinosaurids, Oxalaia was primarily a piscivore, meaning it specialized in hunting fish. Its long, narrow snout, conical teeth (ideal for gripping slippery prey), and nostrils positioned further back on the skull (though this part is not preserved in Oxalaia, it’s inferred from relatives) were all adaptations for a fish-eating lifestyle. It likely waded into shallow waters or swam to catch fish, possibly using its snout to sense movement in murky water. While fish were its main food source, it may have also opportunistically eaten other small animals or scavenged carcasses when available.

Significance and Ongoing Research

The discovery of Oxalaia is significant for several reasons. It represents one of the largest theropods found in Brazil and South America, highlighting the diversity of giant predators on the continent during the Cretaceous. It also extends the known geographic range of large spinosaurine spinosaurids to South America, providing further evidence of faunal connections between South America and Africa during this period, as these landmasses were still relatively close after the breakup of Gondwana. The close resemblance to Spinosaurus supports this connection.

Ongoing research and future fossil discoveries are crucial for a more complete understanding of Oxalaia. Paleontologists hope to find more complete skeletal remains to confirm its size, detailed anatomy, and lifestyle. Further study of the Alcântara Formation continues to reveal more about the ancient ecosystem Oxalaia inhabited and its interactions with other prehistoric life. Clarifying its exact evolutionary relationships with other spinosaurids, particularly Spinosaurus, remains an active area of paleontological investigation, depending heavily on new fossil finds.