Name: Dacentrurus armatus
Etymology: From the Greek "da" (very), "kentron" (sharp point) and "oura" (tail); and from the Latin for "equipped with armour"
Distribution: Late Jurassic (Kimmeridgian) of England
Type Specimen: Partial skeleton including the pelvis, femur and some vertebrae
Estimated size: 10 m long and 4.5 m wide
It must have been amazing to be a palaeontologist in England in the 19th century. The term 'Dinosauria' was coined by Richard Owen in 1842 to classify all the seemingly 'weird' reptile fossils being discovered across England and mainland Europe. And then for Owen to find and describe something like Dacentrurus armatus in 1875, unrecognisable even within the newly formed 'Dinosauria', would have caused a stir!
As more species of Dacentrurus were described, it became clear that it possessed sharp spines that ran along the whole length of the spine to the tip of its tail, forming a 'thagomizer' - it is still not certain whether the thagomizer was used for display or defensive purposes. It was also one of the larger stegosaurs, with average stegosaur length measuring around 5.5-6 m. Of course, when working with small sample sizes, it's hard to clarify whether fossils found are truly representative of their species, or whether they were abnormally small or large!
Owen, R. 1875. Monographs of the fossil Reptilia of the Mesozoic formations (Pt. II) (genera Bothriospondylus, Cetiosaurus, Omosaurus). Palaeontographical Socoiety Monographs 29; 15 - 93.