Istiorachis macarthurae: New Sail-Backed “Short King” from Isle of Wight – Was Its Towering Sail for Courtship or Intimidation?

In a landmark August 2025 Papers in Palaeontology paper, Jeremy Lockwood and colleagues have named Istiorachis macarthurae, a flamboyant new iguanodontian from the Early Cretaceous WesSєx Formation (~125 million years ago) on England’s Isle of Wight. At roughly 6–7 metres long, this “short king” possessed one of the most elaborate sails ever seen in an ornithopod—an array of extremely elongated neural spines rising dramatically above the back and anterior tail.

The sail, formed by hyper-elongated vertebrae, was far taller and more decorative than typical iguanodont structures. Its striking profile likely served dual functions: visual display for courtship and intimidation of rivals or predators. Colour patterns and blood-vessel impressions preserved in related specimens suggest the sail could flush or change appearance, much like modern lizard dewlaps or bird crests.

Named after record-breaking sailor Dame Ellen MacArthur, Istiorachis (“sail spine”) lived in the lush, riverine floodplains of southern England alongside other iguanodontians, ankylosaurs, and theropods. Its modest size compared with giant relatives such as Iguanodon highlights remarkable morphological disparity within Early Cretaceous ornithopods.

“This sail was not for thermoregulation or swimming—it was a billboard,” Lockwood stated. The discovery underscores how display structures evolved independently across dinosaur groups and adds to the Isle of Wight’s status as one of Europe’s richest dinosaur localities.

After decades of scrappy remains, Istiorachis has delivered a vivid portrait of a flamboyant herbivore that used its spectacular sail to attract mates and deter threats in the Wealden world.