Einiosaurus
Name:
Einiosaurus
(Buffalo lizard).
Phonetic: Ay-nee-o-sore-us.
Named By: Scott Sampson - 1995.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Ceratopsia, Ceratopsidae, Centrosaurinae,
Pachyrhinosaurini.
Species: E. procurvicornis (type).
Diet: Herbivore.
Size: About 4.5 meters long.
Known locations: USA, Montana - Two Medicine
Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: 3 skulls and several
hundred bones from at least 15 individuals.
The
nasal horn of Einiosaurus is quite unusual in that
it curves forward to
point towards the ground, something which is reflected in the species
name E. procurvicornis which translates to
English as 'forward
curving horn'. In young Einiosaurus this horn
is thought to have
started out small, but as the individual grew the horn got larger and
more curved until it reached the extremes in what are thought to be
adult specimens. This strongly suggested that the curved horn was a
sexually selected characteristic that was most developed in the largest
and most mature individuals, although it is not certain if males and
females shared the same level of development.
The
curving of this horn is thought to have ultimately evolved to touch
upon itself to form the nasal bosses that are present in other related
centrosaurine ceratopsians
like Pachyrhinosaurus
and Achelousaurus.
Ultimately this suggests that Einiosaurus was more
basal than
pachyrhinosaurine members of the Centrosaurinae, yet itself was more
advanced than others such as Centrosaurus.
As
a centrosaurine ceratopsian, Einiosaurus had a
short neck frill
compared to the chasmosaurine ceratopsians like Chasmosaurus.
On the
top of this neck frill were two large horns that projected upwards from
the top, a feature similar to Diabloceratops.
Further smaller horns
were placed along the outer edges of the neck frill, and although
these horns were most probably for the purpose of display, it’s
conceivable that these horns would have offered a little more
protection against large tyrannosaurid
predators like Gorgosaurus,
and particularly Daspletosaurus
which was thought to have been better
suited to tackling ceratopsians. Still these frill horns may have
best only served to intimidate predators rather than being of practical
use, especially as part of a herds group display.
Herding
behaviour has been attributed to Einiosaurus due to
the discovery of a
bone bed that yielded the remains of at least fifteen individuals.
Einiosaurus was the only ceratopsian in this
bone-bed, and other
micro fossils of aquatic molluscs suggest that the ground would have
once been underwater. Two theories exist for this occurrence, the
first of which is that a herd of Einiosaurus
clustered around a
diminishing water hole during the dry season that was not replenished
by rain in time to save the herd. Another and often more widely
accepted theory is that the Einiosaurus drowned
while trying to cross a
river, a theory that has been proposed to explain the presence of
other ceratopsian dinosaur bone-beds that exist for Centrosaurus
and
Styracosaurus.
Droughts
and flash floods may have been common problems for Einiosaurus
to deal
with as they seem to have lived in a semi-arid inland environment.
Rivers would have not only been one of the few sources of water but
also formidable barriers as Einiosaurus moved on to
fresh grazing
areas. The plants of this environment would have been considerably
tougher than the lush vegetation of wetland areas, but Einiosaurus
possessed typical ceratopsian features that allowed it to eat these
kinds of plants. The first was a sharp beak that was easily capable
of shearing through though and fibrous stems. The mouth had a battery
of specialised teeth that were easily capable of grinding tough plant
material so that it could be easily digested.
The
name Einiosaurus is a combination of the Blackfeet
'eini'
(buffalo) and the Ancient Greek 'saurus' (lizard).
Further reading
- Two new horned dinosaurs (Ornithischia: Ceratopsidae) from the Upper
Cretaceous Two Medicine Formation, Montana, USA. - Journal of
Vertebrate Paleontology 15 (4): 743–760. - Scott D. Sampson - 1995.
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