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ANATOMY
Stegosaurus was up to 26-30 feet long (8-9 m), about 9 feet
tall (2.75 m), and weighed about 6,800 pounds (3100 kg). Its
small brain was only the size of a walnut (weighing roughly
2.5 - 2.9 ounces (70 - 80 grams). Its skull was long.
pointed, and narrow; it had a toothless beak and small cheek
teeth. Its head was carried close to the ground, probably no
more than 3 feet (1 m) high.
Stegosaurus had 17 bony
plates that were embedded in its back. The arrangement of
these plates was unknown until a 1992 Stegosaurus find in
Colorado (Carpenter, et al.) - the plates ran along the
Stegosaurus' back and tail in two rows, and the plates
alternated in alignment.
The function of these
plates is uncertain. The plates were made of bone which was
not solid, but was filled with tube-like tunnels. The
largest of these triangular plates was about 2.5 ft (76 cm)
tall and just as long. The plates were probably
well-nourished by blood vessels, indicating that the plates
may have been used to regulate the dinosaur's temperature.
They may have also been used for protection or mating
display purposes.
Stegosaurus also had
spikes at the end of its flexible tail (these are called
thagomizers;
they were named for a Gary Larson "Far Side" cartoon in
which a caveman is explaining that the end of a Stegosaurus'
tail is called a thagomizer, named for the late Thag
Simmons). These spikes were up to four feet long and were
used for protection from predators; they pointed to the
sides of the tail. Different species of Stegosaurus had
different numbers of tail spikes; Stegosaurus ungulatis
had 8 spikes and Stegosaurus stenops had 4 spikes.
Some early Stegosaurus had shoulder spines.
As even more protection,
Stegosaurus had armor-like scutes on the skin of the neck,
the pelvic area (the hips) and perhaps on the sides of some
species. These bony scutes were dicovered by Carpenter, et.
al. in 1992.
Stegosaurus' rear legs
were longer and straighter than its front legs, which
sprawled out to the sides. The forefeet (the feet of the
front legs) had five short, wide toes with short, hoof-like
tips. The rear feet had three short, wide toes with hooves.
DIET AND TEETH
This plated dinosaur was an herbivore (it ate only plants).
It must have eaten a large amount of low-calorie plant
material each day to sustain its bulk, probably using its
toothless beak to get food. There is debate on whether or
not Stegosaurus could rear up on its rear legs to forage for
vegetation. If it couldn't rear up, it was limited mostly to
plants no taller than about 3 feet (1 m) tall. This would
have included
ferns, smaller club mosses, cycads,
horsetails, and bushy conifers.
PREDATORS OF STEGOSAURUS
It isn't known with any certainly, but possible predators of
Stegosaurus include all the large meat-eaters from western
North America during the
late Jurassic Period.
Some of these meat-eaters included
Allosaurus,
Ceratosaurus,
Marshosaurus, Torvosaurus, and maybe even packs of smaller
meat-eaters like
Ornitholestes.
STEGOSAURUS' PLATES
Stegosaurus' many plates were embedded with a network of blood vessels.
This suggests that these plates were probably used for the
collection and dispersion of heat. If Stegosaurus used the
plates to regulate its body heat, then Stegosaurus was
ectothermic
(cold-blooded)
WHEN STEGOSAURUS LIVED
Stegosaurus lived during the late
Jurassic Period,
about 156-140 million years ago. There was no polar ice
during the last two-thirds of the Jurassic. The climate was
warm and moist and the sea levels high. There were vast
flooded areas, temperate and subtropical forests, and coral
reefs. The extensive water moderated the seasonality.
There was a minor mass
extinction toward the end of the Jurassic period. During
this extinction, most of the stegosaurid and enormous
sauropod dinosaurs died out, as did many genera of ammonoids,
marine reptiles, and bivalves. No one knows what caused this
extinction.
LOCOMOTION
Stegosaurus' back legs were twice as long as its front legs.
It is generally though to have walked on all four legs (quadtupedal),
but it may have reared up on its large hind legs to get
vegetation.
BEHAVIOR
Stegosaurus, like other Stegosaurians, may have been a
herding animal, but this is far from certain.
INTELLIGENCE
Stegosaurus had a very tiny brain - it was only the size of
a walnut. This is especially small, given that Stegosaurus
was up to 26-30 feet (8-9 m) long! It used to be thought
that Stegosaurus had a second brain (which it would seem to
need given that the brain in its head was very, very tiny).
Paleontologists now think that what they thought was a
second brain was just an enlargement in the spinal cord in
the hip area. This enlargement was larger than the animal's
tiny brain. There is debate about what this enlargement
contained - fatty tissue or nerves. This sacral ganglion,
larger than the animal's tiny brain, may have contained both
nerves and fatty tissue. This nerve center may have
controlled the animal's hind legs and tail.
Stegosaurus was a stegosaurian (stegosaur), whose
intelligence (as measured by its relative brain to body
weight, or EQ) was relatively low among the dinosaurs.
DISCOVERY OF FOSSILS
Many fossils of Stegosaurus have been found in western North
America (Utah, Wyoming, and
Dinosaur Ridge, Colorado),
western Europe, southern India, China, and southern Africa.
The
first Stegosaurus fossil
was found in Colorado, USA, in 1876 by M. P. Felch.
Paleontologist
Othniel C. Marsh named Stegosaurus in 1877. The
most complete Stegosaurus yet found
(nicknamed Spike) was discovered near Canon City, Colorado,
USA in 1992 by Bryan Small, Tim Seeber, and Kenneth
Carpenter. Only one set of Stegosaurus footprints have been
found so far, and they were
stolen from Western Australia in 1996.
CLASSIFICATION
Stegosaurus was an herbivorous
ornithischian
dinosaur, belonging to the group Thyreophora (also called
Enoplosauria, they were dinosaurs with dermal armor,
including both the stegosaurs and the ankylosaurs, as well
as some others) and the group Stegosauridae (which includes
Kentrosaurus,
Tuojiangosaurus, and others). Stegosaurus was the largest
and one of the last of the stegosaurids. The type species is
S. armatus. (Return to
FOSSILS index) |
