Meaning
Sail backbone
Length
up to 7 metres (23 feet)
Classification
Ornithopoda,
Iguanodontidae Cope, 1869
Iguanodontia, Baur 1891
Ankylopollexia, Sereno 1986
Styracosterna, Sereno 1986
Istiorachis macarthurae Lockwood, Martill and Maidment, 2025
Locations
Istiorachis was originally found at Grange Chine, in a 1.5-m-thick bed that has occasionally yielded dinosaur remains, including the holotype specimen of the tyrannosauroid theropod Eotyrannus lengi.
Unfortunately the excavation site was poached and an unknown amount of the skeleton was taken before collection could be completed.
Istiorachis was a herbivorous dinosaur, feeding on the plants, such as conifers, cycads and tree-ferns that are found in the Wessex Formation.
Istiorachis differs from all other iguanodontians by possessing one autapomorphy, namely two anterior parasagittal tuberosities present on the ventral surface of a posterior dorsal vertebra, marking a change from vertebrae with a ventral keel to a flat surface. A posterior cervical vertebra has a damaged anteroventral process at the base of the neural spine, potentially representing a second autapomorphy. Istiorachis also possesses the following features, which, although not unique to the taxon, occur in a unique character combination.
- An interpostzygapophyseal fossa and tubular cavity is located between the origin of the postzygapophyses and above the neural canal: a similar fossa is also seen in Lesothosaurus diagnosticus, Camptosaurus dispar, Iani smithi, Mantellisaurus atherfieldensis, Tanius sinensis and Eolambia caroljonesa.
- A strongly developed centropostzygapophyseal lamina is present, especially in the anterior dorsal vertebrae.
- Dorsal neural spines hyperelongated to over fourfold the height of the anterior articular surface of the centrum, as also occurs in the non-hadrosaurids Ouranosaurus nigeriensis and Morelladon beltrani.
- Ischium with sinusoidal shaft in lateral view, as also seen in Bactrosaurus johnsoni and Gilmoreosaurus mongoliensis.
- Ischium with strongly developed distal boot with an anteroposterior diameter 3.3-fold as wide as the midshaft, as also seen in Bactrosaurus johnsoni and Eolambia caroljonesa
LOCKWOOD, J. A. F., MARTILL, . M. and MAIDMENT, S. C. R. (2025-08-21). 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): e70034. doi:10.1002/spp2.70034