Named By: K. Carpenter, C. A. Miles & K. Cloward - 2001.
Classification: Chordata, Reptilia, Dinosauria, Ornithischia, Stegosauria, Stegosauridae.
Species: H. mjosi (type).
Size: Around 6 meters long.
Known locations: USA - Wyoming - Morrison Formation.
Time period: Kimmeridgian/Tithonian of the Jurassic.
Fossil representation: Almost complete individual missing only the limbs.
famous stegosaur from the Morrison formation is Stegosaurus
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.