Name: Hesperosaurus ‭(‬Western lizard‭)‬.
Phonetic: Hes-per-o-sore-us.
Named By: K.‭ ‬Carpenter,‭ ‬C.‭ ‬A.‭ ‬Miles‭ & ‬K.‭ ‬Cloward‭ ‬-‭ ‬2001.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Ornithischia,‭ ‬Stegosauria,‭ ‬Stegosauridae.
Species: H.‭ ‬mjosi‭ (‬type‭)‬.
Diet: Herbivore.
Size: Estimated abount‭ 6‭ ‬ to 7 meters long.
Known locations: USA‭ ‬-‭ ‬Wyoming‭ ‬-‭ ‬Morrison Formation.
Time period: Kimmeridgian/Tithonian of the Jurassic.
Fossil representation: Almost complete individual missing only the limbs.

       The most famous stegosaur from the Morrison formation is Stegosaurus itself‭; ‬however the discovery of Hesperosaurus is proof that Stegosaurus was not the only dinosaur of its type around here during this point of the Jurassic.‭ ‬Like with Stegosaurus,‭ ‬Hesperosaurus had a series of large plates that ran down the length of its back in an alternating series of placements‭ (‬as opposed to sequenced pairs that are common in older restorations of Stegosaurus‭)‬.‭ ‬The plates of Hesperosaurus are distinguishable from Stegosaurus for being wider than they are tall.‭ ‬Theories about plate function have covered everything from defence to thermoregulation,‭ ‬but the differences in plate shape between different stegosaur genera and species is more indicative of a display purpose so that a‭ ‬specific individual stegosaur could recognise others of its own kind.
       Hesperosaurus also has a four spike thagomizer on the end of its tail,‭ ‬but the spikes seem to fit better when they are angled slightly backwards so that they point away from the body.‭ ‬It is this feature that palaeontologists‭ ‬are confident in declaring‭ ‬as a defensive weapon since a theropod tail vertebrae has been found with thagomizer spike shaped damage to it.‭ ‬Possible predators of Hesperosaurus could include theropod dinosaurs such as Ceratosaurus and Allosaurus‭; ‬in fact it is the latter here that has the thagomizer damaged vertebrae attributed to it.‭ ‬Additionally other fossil evidence suggests that Allosaurus would attack dinosaurs like Hesperosaurus.
       Because of its presence in the Morrison Formation and similar shaped plates,‭ ‬it would be tempting to suggest that Hesperosaurus was closely related to Stegosaurus.‭ ‬However while these two genera are related in that they are the same type of dinosaur,‭ ‬in depth study has revealed that Hesperosaurus is actually more closely related to Dacentrurus,‭ ‬a genus of stegosaur from Europe.

Further reading
- New primitive stegosaur from the Morrison Formation, Wyoming. The Armored Dinosaurs. - Indiana University Press, Bloomington 55-75. - K. Carpenter, C. A. Miles & K. Cloward - 2001.


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