Nodosaurus
Name:
Nodosaurus
(Knobbled lizard).
Phonetic: No-doe-sore-us.
Named By: Othniel Charles Marsh - 1889.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Thyreophoroidea, Ankylosauria, Nodosauridae.
Species: N. textilis (type).
Diet: Herbivore.
Size: Estimated between 4 and 6 meters long.
Known locations: USA, Wyoming & Kansas.
Time period: Late Cretaceous.
Fossil representation: 2 individuals represented
by partial remains. Additional armour scutes.
Just
like with Ankylosaurus,
Nodosaurus is the type genus of a whole group
of armoured dinosaurs, yet it is also one of the most poorly
represented by fossil material. The nodosaurids
are thought to be the
ancestors of the ankylosaurids, although to have continued to thrive
even in the presence of their more heavily armoured relations. The
obvious similarity between nodosaurids and ankylosaurids is the small
pieces of bony armour (referred to as osteoderms, but also called
scutes) that ran across the back and upper flanks of the body. Key
differences include however a lack of a clubbed tail, a narrower
mouth, and the lack of a more advanced nasal system that appears to
be characteristic of the more advanced ankylosaurids.
Although
an exact size for Nodosaurus currently remains hard
to establish, the
fossil material at least indicates that Nodosaurus
was a medium to
large sized nodosaurid. The osteoderms than ran across its back were
rectangular in individual appearance and arranged in bands that ran
down towards the sides. These osteoderms did not extend to the belly
however, and if a large predatory theropod like a tyrannosaur managed
to flip a Nodosaurus over it would be completely
defenceless. The
additional armour along its back meant that the legs of Nodosaurus
had
to become strong enough to accommodate the extra weight, and to
facilitate this they became short and squat with attachments for
stronger muscles. As such the additional weight and shorter stride of
Nodosaurus meant that it could not rely upon speed
and agility to
escape predators, which has led to the idea that Nodosaurus,
as
well as other nodosaurids, may have collapsed to the ground to try an
prevent a large theropod the chance to work its foot under the body and
flip it over into its back.
This
meant that only the armoured back was presented to attackers,
although it is debateable how effective a defence this would have
actually been. In the west tyrannosaurids
like Daspletosaurus
seem to
have been well suited to crunching through tough prey, while in the
east Appalachiosaurus
seems to have been more gracile, but possibly
could have approached other large tyrannosaurids in size. You also
have to consider that if this defence actually worked, there would
have been no need for the later ankylosaurids to evolve special spikes
around the back of their heads, an area that is surprisingly under
protected in many nodosaurids. It is possible that while attack from
a large tyrannosaur could have easily meant the end for Nodosaurus,
such predators were not as numerous as smaller theropods such as
Dromaeosaurus,
that would have more easily been defeated by the
armour while being physically incapable of flipping a Nodosaurus
onto
its back.
Further reading
Notice of gigantic horned Dinosauria from the Cretaceous. American
Journal of Science 38:173-175. - Othniel Charles Marsh - 1889.
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