Hesperosaurus
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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