Name: Polacanthus ‭(‬Many Spikes‭)‬.
Phonetic: Po-la-can-thuss.
Named By: Richard Owen‭ ‬-‭ ‬1865.
Synonyms: Euacanthus.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Ornithischia,‭ ‬Thyreophora,‭ ‬Ankylosauria,‭ ‬Ankylosauridae,‭ ‬Polacanthinae.
Species: P.‭ ‬foxii‭ (‬type‭)‬.
Type: Herbivore.
Size: 4‭ ‬meters long.
Known locations: United Kingdom,‭ ‬Isle of Wight,‭ ‬Sussex.
Time period: Barremian of the Cretaceous.
Fossil representation: Several specimens of individuals,‭ ‬but only the rear has been well preserved.

       Discovered by Reverend William D.‭ ‬Fox in‭ ‬1865,‭ ‬Polacanthus has been frustratingly ill preserved with only the hind quarters and parts of armour well preserved.‭ ‬The skull is also unknown,‭ ‬and for this reason modern reconstructions are based upon comparisons with other similar dinosaurs like Gastonia.
       What can be ascertained is that Polacanthus was a quadrupedal low browser with heavy armour adaptations along its back.‭ ‬These include spikes over much of its body and a huge‭ '‬shield‭' ‬that‭ ‬covered its hips and sacrum.‭ ‬This shield was built up from a mass of osteoderms and was not connected to any bone structure underneath.‭ ‬It could be that the armour was primarily for defence against theropods like Neovenator and Eotyrannus,‭ ‬which would have only been able to bite down from above.‭
       The spikes would've made it difficult to get close without a carnivore impaling its snout,‭ ‬and the sacral armour prevented a bite to the sacrum that could have paralysed Polacanthus.‭ ‬If the tail was also a defensive weapon,‭ ‬the sacral armour would have helped to prevent a predator from disabling its defence.

Further reading
- On a new Wealden saurian named Polacanthus - W. Fox - 1865.
- Polacanthus foxii, a large undescribed dinosaur from the Wealden Formation in the Isle of Wight - J. W. Hulke - 1881.
- The armoured dinosaur Polacanthus foxi, from the Lower Cretaceous of the Isle of Wight - W. T. Blows - 1987.
- A new species of Polacanthus (Ornithischia; Ankylosauria) from the Lower Cretaceous of Sussex, England - W. T. Blows - 1996.
- Espinas dermicas del dinosaurio anquilosaurio Polacanthus en las facies Weald de Salas de Los Infantes (Burgos, España). - Estudios Geológicos 55: 267-272. - X. Pereda-Suberbiola, M. Meijide, F. Torcida, J. Welle. C. Fuentes, L. A. Izquierdo, D. Montero, G. Pérez & V. Urién - 1999.
- New remains of the ankylosaurian dinosaur Polacanthus from the Lower Cretaceous of Soria, Spain. - Cretaceous Research 28: 583–596. - X. Pereda-Suberbiola, C. Fuentes, M. Meijide, F. Meijide-Fuentes & M.J. Meijide-Fuentes - 2007.
- Wealden armoured dinosaurs, by P. M. Barrett & S. C. R. Maidment. In English Wealden fossils. Palaeontological Association, London, Field Guides to Fossils 14, 769 pp, D. J. Batten (ed). - 2011.
- Elementos de la armadura dermica del dinosaurio anquillosaurio Polacanthus Owen, 1865, en al Cretácico inferior de Morella (Castellón, España). - Ameghiniana 48(4): 508-519. - J. M. Gasulla, F. Oretga, X. Pereda-Suberbiola, F. Escaso & J. L. Sanz - 2011.
- First Valanginian Polacanthus foxii (Dinosauria, Ankylosauria) from England, from the Lower Cretaceous of Bexhill, Sussex. - Proceedings of the Geologists' Association 125: 233–251. - William T. Blows & Kerri Honeysett - 2014.
- Osteology and Taxonomy of British Wealden Supergroup (Berriasian–Aptian) Ankylosaurs (Ornithischia, Ankylosauria) - Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1826956. - Thomas J. Raven, Paul M. Barrett, Stuart B. Pond & Susannah C. R. Maidment - 2020.


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