Istiorachis macarthurae: A New Iguanodontian Specimen – Was its “Sail” Used for Charm or Threatening Enemies?

In August 2025, the world of paleontology was “awakened” by the discovery of a new iguanodontian species named Istiorachis macarthurae on the Isle of Wight, England. This species is notable for its incredibly impressive “sail” structure, making it one of the most exciting dinosaur discoveries of 2025.

The fossil was unearthed from the WesSєx Formation (Early Cretaceous, approximately 125 million years ago). The specimen includes a partial skeleton with extremely long neural spines, forming a “sail” running along its back and tail. The genus name Istiorachis comes from the ancient Greek: istion (sail) + rhachis (spine). The species macarthurae is named in honor of Dame Ellen MacArthur – the famous British female sailor who set a record for circumnavigating the globe alone, and who also hailed from the Isle of Wight.

Istiorachis was a medium-sized herbivorous iguanodon (about 1 ton). What set it apart from other iguanodontians was its “extra-long” dorsal spines, which formed a distinctive sail-like structure. Researchers led by Jeremy Lockwood (University of Portsmouth) suggest that this “sail” primarily served visual signaling – aiding in the identification of its kind, and especially in attracting mates (Sєxual selection). However, its function could also be diverse: providing thermal support, increasing body surface area to intimidate predators, or even playing a mechanical role related to its quadrupedal gait.

This discovery adds to the growing list of iguanodontians with long dorsal “sails” or spines in the Early Cretaceous period (Ouranosaurus, Morelladon, Hypselospinus…). It demonstrates the high morphological and behavioral diversity within this group.

As of June 2026, Istiorachis macarthurae remains one of the most talked-about dinosaur species of 2025. The Isle of Wight continues to ᴀssert itself as a “paradise” for iguanodontians with unusual dorsal structures – where dorsal “sails” may have served both to attract and intimidate enemies in the dinosaur world 125 million years ago.