Open Paleo

Istiorachis

Lockwood et al., 2025 ISS-tee-oh-RAH-kiss

From Greek histion (sail) and rhachis (spine); meaning "sail spine", referring to the notably elongated vertebral neural spines

125.8–121.4 million years ago Barremian, Early Cretaceous
Early Cretaceous stages

Istiorachis is an extinct genus of iguanodontian ornithopod dinosaur from the Early Cretaceous (Barremian age) Wessex Formation of the Isle of Wight, England. The genus contains a single species, Istiorachis macarthurae, known from a partial postcranial skeleton including several vertebrae, incomplete ribs, and part of the pelvis. Its vertebral neural spines are notably elongated, giving the animal a 'sail-backed' appearance.

Diagnosis

  1. Two anterior parasagittal tuberosities on ventral surface of posterior dorsal vertebra marking transition from keeled to flat surface
  2. Dorsal neural spines hyperelongated to over fourfold height of anterior articular surface of centrum
  3. Anterior process at base of neural spine in posterior cervical vertebra potentially marking peg-and-socket articulation
  4. Interpostzygapophyseal fossa and tubular cavity between postzygapophyses origins and above neural canal
  5. Strongly developed centropostzygapophyseal lamina especially in anterior dorsal vertebrae
  6. Ischium with sinusoidal shaft in lateral view

Species

Istiorachis macarthurae Lockwood et al., 2025

Type species

Named for Dame Ellen MacArthur, sailor and Isle of Wight native who set the world record for the fastest solo non-stop circumnavigation of the globe in 2005.

Holotype
MIWG 6643 , Dinosaur Isle Museum
Material
Partial skeleton with one cervical vertebra, eight dorsal vertebrae, three dorsal rib heads, partial sacrum, seven caudal vertebrae, both pubes, both ischia
Horizon
L11 Bed, Wessex Formation, Barremian, Early Cretaceous , 125.8–121.4 million years ago
Locality
100 m east of Grange Chine, Isle of Wight, United Kingdom

References

  1. Lockwood, J. A. F.; Martill, D. M.; Maidment, S. C. R. (2025). 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(4). Wiley. doi:10.1002/spp2.70034 lockwood2025a