Istiorachis macarthurae & Thailand’s Giant Spinosaurid: 2025 Discoveries of “Short Kings” and River-Stalking тιтans

Two blockbuster 2025 papers have added striking new chapters to Early Cretaceous dinosaur diversity—one a flamboyant sail-backed “short king” from England, the other a mᴀssive fish-eating spinosaurid from Thailand.

On the Isle of Wight, Jeremy Lockwood and colleagues named Istiorachis macarthurae in Papers in Palaeontology (August 2025). The ~125-million-year-old iguanodontian preserves an ornate sail of extremely elongated neural spines along the back and anterior tail—far taller and more decorative than typical iguanodont sails. Named after record-breaking sailor Ellen MacArthur, the “sail spine” dinosaur likely used its striking structure for visual display or mate attraction in the lush Wealden floodplain. At roughly 6–7 metres long, it was no giant, yet its elaborate ornament made it a standout among styracosternans.

Meanwhile, in northeastern Thailand’s Khok Kruat Formation (~125 Ma), Adun Samathi’s team highlighted a previously unpublished mᴀssive spinosaurid—nicknamed the “Sam Ran spinosaurid”—estimated at over 10 metres long and heavier than a pickup truck. Partial limb, rib, and vertebral material reveals classic spinosaurine traits: elongated snout, conical teeth, and robust forelimbs suited for snatching fish in tropical rivers. This predator coexisted with тιтanosauriforms and smaller herbivores, proving Southeast Asia hosted true giant spinosaurids during the same interval when Istiorachis sailed across Europe.

Together, the discoveries illustrate remarkable morphological disparity within Early Cretaceous ecosystems: ornate display structures in smaller ornithischians versus hyper-specialised aquatic hunting in giant theropods. Both fossils underscore how 2025 continued to reveal that the Early Cretaceous was far more flamboyant and ecologically diverse than previously imagined.