Polacanthus

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)‬,‭ ‬P.‭ ‬rudgwickensis.
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.



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