Spinosaurus is not an aquatic dinosaur

Area of Science:

• Paleontology
• Functional Morphology
• Biomechanics

Background:

• The discovery of Spinosaurus aegyptiacus fossils, including its distinctive sail-back and jaw structure, initially suggested a fish-eating diet.
• Recent findings, particularly the high-spined tail, fueled the 'aquatic hypothesis,' proposing Spinosaurus as the first fully aquatic dinosaur capable of pursuit predation in water.

Purpose of the Study:

• To rigorously test the functional claims of the 'aquatic hypothesis' regarding Spinosaurus aegyptiacus's locomotion and predatory behavior.
• To reconstruct the biomechanics of Spinosaurus aegyptiacus on land and in water using advanced modeling techniques.

Main Methods:

• A CT-based skeletal reconstruction of Spinosaurus aegyptiacus was created from fossil evidence.
• A posable flesh model was developed by adding internal air and muscle to the skeletal reconstruction.
• The model's performance was analyzed for terrestrial bipedalism and aquatic swimming capabilities, with comparisons to extant reptiles.

Main Results:

• The flesh model demonstrated that Spinosaurus aegyptiacus was bipedal on land.
• In deep water, the dinosaur was a slow-surface swimmer (less than 1 m/s) and too buoyant to dive.
• The sail-like structure is more consistent with display than aquatic propulsion, unlike extant aquatic animals with fleshy tail flukes and reduced limbs.

Conclusions:

• Spinosaurus aegyptiacus was not a fully aquatic dinosaur but a semiaquatic predator.
• Its locomotion was primarily bipedal on land, and it was an inefficient swimmer in deep water.
• The dinosaur was likely an ambush piscivore, frequenting the edges of coastal and inland waterways, with evidence of inland range expansion.