Spinosaurus

No large theropod looks like Spinosaurus aegyptiacus. The skull is long and narrow, almost crocodilian, with interlocking conical teeth, sensory pits along the rostrum, retracted nostrils, and a deep robust mandible. Running down its back is a dorsal sail of enormously elongated neural spines (up to 1.65 m in some individuals), covered in skin. The sail was almost certainly for display.

The contentious bits all come from Ibrahim et al. The 2014 paper described a new neotype (FSAC-KK-11888) with dramatically reduced hindlimbs, dense limb bones (a hallmark of aquatic vertebrates), and a centre of mass too far forward for stable bipedalism. The 2020 follow-up described the tail: long, paddle-like, with elongated neural spines and chevrons that gave it a fin-like profile. Ibrahim's team argued Spinosaurus was a true pursuit predator that swam after prey using lateral tail propulsion.

Not everyone is convinced. Hone & Holtz (2017) prefer a wading, heron-like ecology. Sereno et al. (2022) modelled the swimming and concluded it was inefficient compared with actual aquatic predators. The argument is still live.

Whatever the locomotion turns out to be, the diet is not in question. Spinosaurus was a fish-eater. Its close relative Baryonyx has preserved fish scales in its stomach. The snout morphology — sensory pits, conical teeth, raised nostrils — matches modern piscivorous crocodilians and gharials. Stable isotope analysis of the teeth (Amiot et al. 2010) backs up an aquatic-leaning diet. The Kem Kem and Bahariya environments held giant coelacanths, lungfish, and sawfish big enough to feed an animal this size.

The sail was display. Thermoregulation has been proposed for these structures in the past but the biomechanics do not really support it.

• Stromer's holotype — destroyed 1944 in Allied bombing of the Munich Paläontologisches Museum; only photographs and Stromer's monograph remain.
• FSAC-KK-11888 — Ibrahim et al. neotype, Casablanca; basis for the 2014 and 2020 reconstructions.
• Sigilmassasaurus material — sometimes assigned to Spinosaurus, sometimes considered a distinct genus.
• Bahariya Oasis specimens (numerous) — Egyptian Geological Museum, partial.

The aquatic-pursuit hypothesis (Ibrahim et al. 2014, 2020) is the single biggest palaeontology argument of the last decade. The supporting evidence is real: bone density, tail morphology, isotope data, snout sensory architecture. The counter-evidence is also real: Sereno et al. (2022) modelled the swimming and found it inefficient, and the stratigraphy of the neotype has been questioned. Where most palaeontologists land today: heavily piscivorous, heron-like at minimum, probably more aquatic than any other large theropod, and the full-pursuit-predator question is still open. There is also a smaller debate over whether S. maroccanus is a junior synonym of S. aegyptiacus.

Spinosaurus became a celebrity in 2001 when Jurassic Park III used it as the antagonist that defeats a T. rex, a scene palaeontologists hated and the public loved. Prehistoric Planet (2022) presents the modern aquatic-pursuit reconstruction.

• theropoda
• giganotosaurus
• tyrannosaurus-rex

• Ibrahim, N., et al. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345, 1613–1616.
• Ibrahim, N., et al. (2020). Tail-propelled aquatic locomotion in a theropod dinosaur. Nature, 581, 67–70.
• Hone, D. W. E., & Holtz, T. R. (2017). A century of spinosaurs — a review and revision of the Spinosauridae. Journal of Vertebrate Paleontology, 37, e1366543.
• Sereno, P. C., et al. (2022). Spinosaurus is not an aquatic dinosaur. eLife, 11, e80092.
• Stromer, E. (1915). Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. Abh. Bayer. Akad. Wiss.