Istiorachis Sail: Sєxual Display or Rival Intimidation? The “Real Godzilla” Dinosaur’s Flamboyant Back Explained

The towering sail of Istiorachis macarthurae was almost certainly a tool of Sєxual selection — a flamboyant billboard used primarily for attracting mates and secondarily for intimidating rivals, not for thermoregulation or defense.

Led by Jeremy Lockwood of the University of Portsmouth, the 2025 Papers in Palaeontology study examined the hyper-elongated neural spines of the WesSєx Formation specimen. These spines, far longer than in any other iguanodontian, lack the blood-vessel grooves typical of sails used for heat exchange (as in Dimetrodon or Spinosaurus). Instead, they show the lightweight, display-optimized structure seen in modern birds with elaborate crests and tail ornaments.

Sєxual selection is the only hypothesis that fits all evidence: the sail’s extreme size and asymmetry would have made the animal highly visible across floodplains, ideal for courtship displays or rival standoffs. Like the peacock’s tail or the crests of modern hornbills, such costly structures evolve because they signal fitness to potential mates and deter compeтιтors without direct combat.

Defense is unlikely — the sail would have made the animal more conspicuous to predators, not less. Thermoregulation is ruled out by the absence of vascularization and the animal’s relatively small body size (~1 tonne). The most parsimonious explanation remains Sєxual display, with intimidation of rivals as a secondary benefit.

Lockwood noted the sail functioned as “a flamboyant billboard for attracting mates or intimidating rivals.” This discovery reinforces that Sєxual selection drove some of the most extravagant anatomical experiments in dinosaur evolution — turning Istiorachis into the ultimate Early Cretaceous show-off.