Tail-propelled aquatic locomotion in a theropod dinosaur

Area of Science:

• Paleontology
• Vertebrate Zoology
• Biomechanics

Background:

• Non-avian dinosaurs were historically considered exclusively terrestrial.
• Previous theories of semi-aquatic dinosaurs, particularly spinosaurids, remained controversial.
• Spinosaurus aegyptiacus, a large Cretaceous theropod, exhibits various adaptations suggesting a piscivorous and potentially aquatic lifestyle.

Purpose of the Study:

• To provide unambiguous evidence for an aquatic propulsive structure in Spinosaurus aegyptiacus.
• To investigate the biomechanical function of the unique tail morphology of Spinosaurus.
• To compare the propulsive efficiency of Spinosaurus's tail with terrestrial and extant aquatic vertebrates.

Main Methods:

• Analysis of the unique tail morphology of Spinosaurus aegyptiacus, characterized by tall neural spines and elongate chevrons.
• Utilizing a robotic flapping apparatus to measure undulatory forces generated by physical tail models.
• Comparative analysis of thrust and efficiency between Spinosaurus tail models, terrestrial dinosaur tails, and extant aquatic vertebrate tails.

Main Results:

• Spinosaurus aegyptiacus possessed a unique, fin-like tail structure capable of extensive lateral movement.
• The Spinosaurus tail shape generated significantly greater propulsive thrust and efficiency in water compared to terrestrial dinosaur tails.
• Performance metrics of the Spinosaurus tail were comparable to those of extant aquatic vertebrates using vertically expanded tails for swimming.

Conclusions:

• The unique tail of Spinosaurus aegyptiacus served as an effective aquatic propulsive organ.
• These findings support a semi-aquatic lifestyle for Spinosaurus and suggest a broader invasion of aquatic environments by dinosaurs.
• Aquatic adaptations, though less pronounced, are also present in other spinosaurid species, indicating a significant ecological shift within this clade.