Istiorachis
"sail spine"
Type species Istiorachis macarthurae
- Lived
- 133 to 121 million years ago, Early Cretaceous
- Diet
- Herbivore
- Group
- Ornithopods
- Found in
- United Kingdom
- Named by
- Lockwood et al. 2025
Where its fossils were found
The evidence
Today
125 million years ago
Habitat
A low floodplain crossed by winding rivers, with conifer trees and seasonal dry spells. Iguanodon, Hypsilophodon and Polacanthus lived in the Wessex Formation.
Field notes
About Istiorachis
What it was like
Istiorachis was an iguanodont, a plant eater related to Iguanodon, known from backbones, ribs and part of the hips. The spines on its backbones were unusually tall, which would have given it a low sail or ridge along its back.
Scientists think the sail was more likely for display than for controlling body heat.
Its world
It lived in the Early Cretaceous in what is now England. Its bones come from the Wessex Formation, where it shared the land with Iguanodon, the small Hypsilophodon, the armored Polacanthus and the hunters Neovenator and Baryonyx.
How it was found
Lockwood and colleagues named Istiorachis in 2025, from bones that had been found years earlier.
Field gallery
More views of Istiorachis
Scenes reconstructed from the available fossil evidence.
Lived alongside
Found in the same rock formations
A rock formation can hold fossils laid down millions of years apart, so not every animal here met Istiorachis.
The evidence
The science behind Istiorachis
Which parts of the picture come from its own bones, and which come from its relatives.
From its own fossils
- The original skeleton preserves back, hip and tail vertebrae, incomplete ribs and part of the pelvis.
- Unusually tall spines rise from the back vertebrae and may have supported a fleshy sail or ridge.
Borrowed from relatives
- Iguanodon provides a guide to the missing beaked head, supporting limbs and hoof-like toes.
- Ouranosaurus offers a comparison for a sail-backed body.
Still unknown
- The height, thickness and outline of its fleshy sail.
- Whether the sail served mainly for display or had another use.
- Its head shape, hands, feet and color.
Discovery timeline
- 2010Its worldSweetman & Insole
- 2017Close relativeBertozzo, Dalla Vecchia & Fabbri
- 2025Named itLockwood, Martill & Maidment
Key papers
The research behind what we know of Istiorachis
Its world
Explained how floods and debris flows buried plants and animals on the Wessex Formation floodplain.
The plant debris beds of the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England: their genesis and palaeontological significance. Palaeogeography, Palaeoclimatology, Palaeoecology 292: 409-424
Read the paper : The plant debris beds of the Early Cretaceous (Barremian) Wessex Formation of the Isle of Wight, southern England: their genesis and palaeontological significance (opens in a new tab)Close relative
Restudied a mounted Ouranosaurus skeleton and clarified its anatomy, providing a comparison for another sail-backed plant eater.
The Venice specimen of Ouranosaurus nigeriensis (Dinosauria, Ornithopoda). PeerJ 5: e3403
Read the paper : The Venice specimen of Ouranosaurus nigeriensis (Dinosauria, Ornithopoda) (opens in a new tab)Named it
Named a new iguanodont from a partial skeleton with unusually tall backbone spines and suggested that its sail probably served for display.
The origins of neural spine elongation in iguanodontian dinosaurs and the osteology of a new sail‐back styracosternan (Dinosauria, Ornithischia) from the Lower Cretaceous Wealden Group of England. Papers in Palaeontology 11
Read the paper : The origins of neural spine elongation in iguanodontian dinosaurs and the osteology of a new sail‐back styracosternan (Dinosauria, Ornithischia) from the Lower Cretaceous Wealden Group of England (opens in a new tab)
Close relatives
Other members of Styracosterna
Sources: Wikidata