Spinosaurus aegyptiacus was a giant theropod dinosaur of the Late Cretaceous, distinguished by its immense size and highly specialized body plan. Estimated to have reached lengths of up to 15 meters, it was a contender for the largest known carnivorous dinosaur. Its most recognizable features were a towering sail-like structure along its back and an unusually long, narrow skull, which collectively suggest a lifestyle dramatically different from other large land-dwelling predators. Fossil evidence suggests the creature spent significant time in the vast river systems of ancient North Africa, prompting inquiry into its primary food source and unique semi-aquatic existence.
Anatomical Clues to Feeding
The skull of Spinosaurus provided the first major evidence for a specialized diet, deviating entirely from the deep, robust skulls of bone-crushing theropods. Its snout, or rostrum, was elongated, low, and surprisingly narrow, bearing a strong resemblance to the jaws of modern crocodilians. This morphology was designed for quick, snapping strikes rather than sustaining the high bite forces needed to tear through large terrestrial prey.
The teeth were straight, conical, and smooth, lacking the serrated edges characteristic of most meat-eating dinosaurs. These simple, pointed teeth were perfectly suited for piercing and gripping slippery, struggling fish, preventing them from escaping the jaws. The front of the snout also featured an interlocking arrangement of teeth, forming a structure known as a terminal rosette that maximized the grip on captured aquatic animals.
A network of tiny openings (foramina) covered the snout, similar to those found on modern crocodilians. These openings connected to an internal cavity that likely housed neurovascular structures, functioning as pressure receptors to sense movements in the water. This enhanced tactile sensitivity would have allowed Spinosaurus to detect the pressure waves created by swimming prey, enabling it to hunt effectively even in murky or low-light conditions. The external nostrils were also positioned high up on the skull, allowing the dinosaur to keep its snout partially submerged while still breathing comfortably.
Direct Evidence of Aquatic Prey
The anatomical inference is supported by direct fossil evidence from its close relatives within the Spinosauridae family. An incomplete skeleton of the European spinosaurid Baryonyx was discovered with acid-etched fish scales and bones in its stomach region, proving piscivory. Analysis of Spinosaurus teeth using oxygen isotopes also revealed that the animal was exposed to aquatic environments for long periods, reinforcing the idea of a river-dwelling existence.
The environment in which Spinosaurus lived, the Cretaceous river delta systems of what is now Morocco and Egypt, was teeming with massive aquatic life. This habitat was home to gigantic fish, including the huge, lobe-finned coelacanth Mawsonia and the massive, saw-snouted ray Onchopristis numidus, which could reach eight meters in length. These colossal fish represent a readily available and substantial food source that could have sustained a predator the size of Spinosaurus.
The abundance of Spinosaurus teeth found in the sedimentary river deposits of the Kem Kem Group further supports this aquatic focus. Because dinosaurs continually shed teeth throughout their lives, this concentration suggests the animal spent a significant amount of time actively hunting and losing its teeth directly into the river system.
Opportunistic Terrestrial Foraging
While evidence points to a primary diet of large fish, Spinosaurus was a massive carnivore not strictly limited to aquatic prey. It was likely an opportunistic feeder, supplementing its diet with land animals when the chance arose. This flexibility would have been an advantage during periods of drought or when river levels dropped, making fish harder to catch.
Spinosaurids occasionally preyed on or scavenged dinosaurs, such as juvenile Iguanodon, indicating a willingness to consume terrestrial meat. Spinosaurus would have possessed the strength and size to subdue smaller or medium-sized dinosaurs that ventured too close to the water’s edge. Nevertheless, its specialized anatomy was not optimized for the fast pursuit or bone-crushing bites of land-based theropods, suggesting that any terrestrial foraging was secondary to its aquatic hunting.
Reconstructing Hunting Behavior
The evidence synthesizes into a clear picture of how Spinosaurus procured food in its riverine habitat. Studies of its internal bone structure reveal osteosclerosis (unusually dense and solid leg bones and ribs). This increased bone mass, similar to that found in modern aquatic animals like penguins and hippopotamuses, would have provided ballast, aiding in buoyancy control and allowing the dinosaur to submerge its body for deep wading or even diving.
The tail was highly specialized, possessing tall, paddle-like neural spines and chevrons that formed a flexible, fin-like structure. Biomechanical models of this tail show it was capable of powerful lateral movement, generating thrust for active underwater propulsion, unlike the stiff, tapering tails of other large theropods. This adaptation suggests Spinosaurus was not merely a wader but a capable swimmer, able to actively pursue fish in the water column.
The likely hunting technique involved slow movement through the shallows or ambushing prey near the water surface. Using its dense bones to maintain stability and its specialized snout to sense movement, Spinosaurus could swiftly snap its jaws shut on passing fish. Its powerful forelimbs, equipped with large, curved claws, may have also been used to hook, strike, or hold onto slippery, struggling aquatic prey before delivering a fatal bite.