Stegosaurus
Name: Stegosaurus
(Roof lizard).
Phonetic: Steg-oh-sore-us.
Named By: Othniel Charles Marsh - 1877.
Synonyms: Diracodon, Hypsirhophus.
Classification: Chordata, Reptilia,
Dinosauria,Ornithischia, Thyreophora, Stegosauria, Stegosauridae.
Species: S. stenops (type),
S. ungulatus, S. sulcatus.
Type: Herbivore.
Size: Largest individuals up to 9 meters long.
Known locations: USA, Colorado, Montana, Oklahoma,
Utah, Wyoming, mostly associated with the Morrison Formation. Portugal
- Alcoba�a Formation.
Time period: Kimmeridgian to the Tithonian of the
Jurassic.
Fossil representation: Many individuals found,
Stegosaurus is one of the better represented
dinosaurs in the fossil
record.
With
its
distinctive back plates, Stegosaurus is one of
the best represented
dinosaurs in popular culture today. Initially thought to just
live in the USA, a partial skeleton discovered in 2006 places
Stegosaurus in Portugal. This has significantly
increased the known
range of this animal and further reinforced the theory that North
America and Europe would have been connected during this time.
Living
the life of a low
browser in the Jurassic, Stegosaurus seems to
have concentrated upon
eating soft and leafy vegetation that did not require much effort to
chew. Studies have shown that Stegosaurus
probably did not have much
bite force, but the shape of its teeth would do most of the work for
it. Fossilised teeth show extra wear on the sides where they would
have been sharpest, meaning all Stegosaurus would
have to do is bite
onto the plant and pull its head back and its teeth would cut through
the soft vegetation. Because
of the aforementioned
method of eating, Stegosaurus probably relied
upon its gut to do the
main work in breaking down the plant material for nutrients, and may
have swallowed stones for use as gastroliths to aid this process.
Kentrosaurus, Miragaia, Tuojiangosaurus, Dacentrurus.
Stegosaurus
had a body type
similar to many other stegosaurids
in that the hind legs were much
longer than the fore legs, carrying the hips high above the rest of
the body. When first discovered it was thought that Stegosaurus
could
have been bipedal, and this continued until examination of the
forelegs combined with the estimated bulk and weight of the animal had
Stegosaurus re-cast as a quadruped. Although now
known to be
quadrupedal, most of the weight seems to be balanced towards the hips
and carried by the hind legs, giving Stegosaurus
a reasonably tight
turning arc that could have been very useful in defending itself.
Another advantage of the high hips is that the head is always held
closer to the ground and nearer its food sources, while the tail and
thagomizer (arrangement of spikes) would be always carried at a
height that would allow for a body strike on an attacking predator.
It
goes without saying that
Stegosaurus is most famous for the plates that run
along its back, in
fact its name meaning ‘roof lizard’ is in reference to them. The
plates themselves are specially developed osteoderms that have no fixed
join with the skeleton. When named, the plates were mistakenly
placed flat across its back like the tiles on a roof, hence the name
‘roof lizard’. Discovery of more complete fossils later revealed
that they were placed vertical as opposed to horizontal. However they
were then placed in a single row which in itself caused problems as the
plates would overlap. The third arrangement was of the more familiar
double row configuration, with the plates being arranged in pairs to
one another. There was still a problem with this in that each plate
was different in size meaning there could be no true pairs as they were
all different. This has led to the fourth arrangement which has been
generally accepted since the second half of the twentieth century.
This arrangement is two rows of plates in an alternating
configuration, meaning that when viewed from the side there would be
no gaps of daylight between the plates. Some have called this
configuration into question on the basis that there is no other
precedent for the arrangement, but that does not mean that the
current accepted arrangement is wrong. The world of natural history
is full of ‘freaks’ that don’t seem to make sense, yet continue
to thrive regardless of how much sense their adaptations make to us.
If
the placement of the
plates was not confusing enough the function of them has been even more
demanding of understanding. One theory that can be discounted is the
one of defence. While large and impressive, the plates were
actually very fragile and would not have been able to withstand much
punishment. The second theory is that of thermoregulation, and the
evidence to support this comes from grooves in the plates that would
have allowed blood vessels to run through them. The blood would then
be carried close to the skin where temperature adjustment could take
place. The third theory, one that has rapidly gained more credence
amongst the paleontological community is that they were used for
display, particularly for intimidating rivals and attracting mates.
This may have involved the flushing of blood into the plates to
provide a vivid colour display necessitating the need for blood vessels
in the plates. One argument against both thermoregulation and colour
change is that the plates would have been covered with keratin, which
does not allow for efficient heat exchange or rapid visual colour
change.
Another
body part that has
had to be revised is the thagomizer. Early representations had the
spikes arranged in upward angles, but with further study they are now
accepted to have stuck out to the sides. It’s likely that it was
the thagomizer that was the primary form of defence. Although the
plates that ran down the tail would be of a hindrance to its
flexibility, Stegosaurus would likely been able
to pivot on its hind
legs easily keeping its tail presented to an attacking predator. In
fact, remains of an Allosaurus
have been found
that show a serious
injury to the tail vertebrae that upon examination appears to have been
caused by a thagomizer spike from a Stegosaurus.
Ceratosaurus, Saurophaganax, Allosaurus, Torvosaurus.
The final area of contention is the cavity in the spinal cord of the hip region. This was once conceived as a nerve cluster which was then in turn misinterpreted as a second brain, perhaps in compensation for its actual brain which has famously been described as the size of a walnut. In reality the second brain theory is impossible in the realms of known science. Thankfully however this cavity is not exclusive to Stegosaurus, it also seems to appear in other dinosaurs and more importantly modern birds. Study of this body has given rise to the notion that it is a glycogen body. This body allows for the storage of excess glycogen, a molecule that is used for energy storage in animals and fungi. While the precise method of use is uncertain this may have acted in a way similar to an adrenaline burst in the flight or fight reflex. With the release of glycogen, the muscles would get a sudden burst of energy allowing for more active movement, perhaps for the swinging of the thagomizer at an attacking Allosaurus.
A former species, S. longispinus, was named as a new genus called Alcovasaurus in 2016.Further reading
- A new order of extinct Reptilia (Stegosauria) from the Jurassic of
the Rocky Mountains. - American Journal of Science 3 (14): 513–514. -
Othniel Charles Marsh - 1877.
- Restoration of Stegosaurus. - American Journal of
Science 3 (42):
179–81. - Othniel Charles Marsh - 1891.
- Osteology of the armored Dinosauria in the United States National
Museum, with special reference to the genus Stegosaurus.
- Series:
Smithsonian Institution. United States National Museum. Bulletin 89. -
C. W. Gilmore - 1914.
- Plates of the dinosaur Stegosaurus:Forced
convection heat loss fins?
- Science 192 (4244): 1123–25 - J. O. Farlow, C. V. Thompson &
D. E. Rosner - 1976.
- Taphonomy and paleoecology of the dinosaur beds of the Jurassic
Morrison Formation. - Paleobiology 6 (2): 208–232. - Peter Dodson, A.K.
Behrensmeyer, Robert T. Bakker & John S. McIntosh - 1980.
- Juveniles of the stegosaurian dinosaur Stegosaurus
from the Upper
Jurassic of North America. - Journal of Vertebrate Paleontology 2 (1):
47–62. - P. M. Galton - 1982.
- Growth and Function of Stegosaurus Plates. -
Paleobiology 12:
459–73.- Buffr�nil - 1986.
- Armor of Stegosaurus stenops, and the taphonomic
history of a new
specimen from Garden Park Colorado". The Upper Jurassic Morrison
Formation: An Interdisciplinary Study. Part 1. Modern Geol. 22. pp.
127–44. - K. Carpenter - 1998.
- Comparative histology, growth and evolution of archosaurian
osteoderms: why did Stegosaurus have such large
dorsal plates?. Journal
of Vertebrate Paleontology 56A (20). - R. P. Main, K. Padian &
J. Horner - 2000.
-New Evidence of Shared Dinosaur Across Upper Jurassic Proto-North
Atlantic: Stegosaurus From Portugal. -
Naturwissenschaften 94 (5):
367–74. - F. Escaso, F. Ortega, P. Dantas, E. Malafaia, N. L. Pimentel,
X. Pereda-Suberbiola J. L. Sanz, J. C. Kullberg, M. C. Kullberg, F.
Barriga - 2007.
- Species of plated dinosaur Stegosaurus (Morrison
Formation, Late
Jurassic) of western USA: new type species designation needed. - Swiss
Journal of Geosciences 103 (2): 187–198. - P. M. Galton - 2010.
- A model for the bite mechanics in the herbivorous dinosaur
Stegosaurus (Ornithischia, Stegosauridae). _ Swiss
Journal of
Geosciences 103 (2): 235. - Reichel Miriam - 2010.
- Stegosauria: a historical review of the body fossil record and
phylogenetic relationships, - Swiss Journal of Geosciences 103(2):
199-210 - S. C. R. Maidment - 2010.
- Internal vascularity of the dermal plates of Stegosaurus
(Ornithischia, Thyreophora). - Swiss J Geoscia 103 (2): 173–85. - James
O. Farlow, Shoji Hayashi & Glenn J. Tattersall - 2010.
- The plated dinosaur Stegosaurus longispinus
Gilmore, 1914
(Dinosauria: Ornithischia; Upper Jurassic, western USA),
type species of Alcovasaurus n. gen. - Neues
Jahrbuch f�r
Geologie und Pal�ontologie - Abhandlungen 279(2): 185-208.
- Peter M. Galton & Kenneth Carpenter - 2016
----------------------------------------------------------------------------
Random favourites
 |
 |
 |
 |