- Stegosaurus: “Roofed lizard”
- Height: 4 meters
- Length: 9 meters
- Weight: 3 tons
- Time Period: Jurassic Period (155-145 MYA)
The state dinosaur
of Colorado and one of the most iconic members of Dinosauria, Stegosaurus,
has a lot of history and theories surrounding it including; where it was found,
its behavior, and how it lived. As with most fossilized organisms, there is
only so much information that can be gleaned from the material and, because of
this, some aspects of its anatomy and behavior can easily be inferred due to
the connections that can be made between the animal and its relatives. Stegosaurus has earned its spot as one
of the most iconic dinosaurs due to the profound amounts of remains that have
been uncovered that allows Paleontologists to understand more about Stegosaurus than other, more fragmentary
species.
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| (Copyright belongs to the Artist; Robert Nicholls) |
The Bone Wars was a
period of extreme increases in the collecting and discovery of as many fossils
as possible due to a rivalry between two Paleontologists Edward Drinker Cope
and Othniel Charles Marsh. During the Bone Wars, many new species of previously
unknown organisms were discovered. Othniel Charles Marsh originally discovered Stegosaurus in 1877 in Morrison,
Colorado. When Othniel Charles Marsh found the remains, he initially thought
they belonged to a turtle-like animal thinking that the large plates overlapped
one another along the back, but he later retracted this theory for the one
accepted today which is to say, the plates lined the back standing vertically.
In 1886, Marshal Felch discovered remains of a separate species of Stegosaurus, dubbed sulcatus, in Cañon City, Colorado. The largest Stegosaurus could stand four meters high at the tallest back plate
and could reach lengths of up to nine meters that, in contrast, is the size of
a modern bus. But the size alone is not what sets Stegosaurus apart from the other animals it shared its ecosystem
with.
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| (Copyright= Public Domain) |
The Plates that
line the spine of Stegosaurus are still very much an enigma. Paleontologists have put forth many theories over the
years regarding the use of the plates. When Othniel Charles Marsh first found
the remains, he thought the plates lay flat against the body like the armor of
a Pangolin. Marsh later revoked this theory for the much more familiar one that
is in use today, in which the plates stand up vertically along the back.
Through the years, Paleontologists have refined the theory regarding the exact
configuration of the dorsal osteoderms which went from two lines of identical
plates on the back (this theory has been found to be incorrect due to a second,
identical, row of plates mirroring the other having never been found), to one
row of plates that alternate. What these plates were used for is still up for
debate and has been ever since the animal’s discovery. Many scientists have
posed theories as to the purpose of the plates including Robert Bakker, World renowned
Paleontologist and curator of the Houston Museum of Nature and Science,
speculated that the plates of Stegosaurus
were the inside, or core, of a bigger plate made of a keratinous material.
Bakker also suggested that these horny outgrowths could be semi-movable and the
animal might have been able to use them as a sort of defense, splaying them out
to the sides to deter predators from coming too close. The other theories
include, temperature regulation like the large flat area of an elephant’s ear,
to appear larger to predators, and as a sexual display to the opposite sex.
Many Paleontologists presently accept that the plates would have had multiple
uses and could have been used for any one of these theories as well.
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| (Copyright of skeletal belongs to; Scott Hartman, Copyright for plate belongs to TaylorMadeFossils) |
Even if the plates
of Stegosaurus were not used for
defense, Stegosaurus also carries
with it four spike-like osteoderms on the end of its tail. These spines bent
outward to the sides and backwards and could have been used an incredible
defense against many of the large predators of the Morrison Formation. In 2014,
Robert Bakker found evidence in the pelvis of the Mid-Jurassic Carnivore, Allosaurus, at the Glenrock
Paleontological Museum in Glenrock, Wyoming. Bakker found that there was a
large open hole in the pubic bone of one of the mounted Allosaurus skeletons and later revealed that the wound fit the tail
spike of a Stegosaurus (informally
known as a Thagomizer) almost perfectly. Evidence suggests that bacteria,
fragmentary bone, and other debris stayed in the wound and infected the area
until it eventually killed the animal. According to Robert Bakker, “A massive
infection ate away a baseball-sized sector of the bone, Probably this infection
spread upwards into the soft tissue attached here, the thigh muscles and
adjacent intestines and reproductive organs.” This theory was also reinforced
by the fact that the vertebrae in the tail of Stegosaurus had no locking
mechanisms and could be swung in many directions as Bakker points out, “Most
dinosaur tails get stiffer towards the end, The joints of a stegosaur tail look
like a monkey’s tail; They have no locking joints and were built for
3-dimensional combat.” This heavily points to the Thagomizer of a Stegosaurus being used a powerful
defense mechanism towards anything it perceived as a threat. Although
Stegosaurus was unique in the family Dinosauria,
it wasn’t the first or last of its kind.
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| (Copyright of art belongs to; Robert Bakker), Copyright of Fossil segment is Public Domain) |
Since Stegosaurus was the first of its kind to
be discovered, its phylogenic suborder and family were named after it. After Stegosaurus’ discovery many other
members of Stegosauridae were discovered
including; Kentrosaurus, Dacentrurus,
Lexovisaurus, Miragaia, and
Hesperosaurus from different parts of the world like Africa and Europe.
These relatives generally all shared a similar body plan as Stegosaurus only variations being the
plates, spines, and skull shapes. Stegosaurus
existed from the early Jurassic to the early Cretaceous and then went extinct,
most likely due to other more successful herbivores taking over the Stegosaur niche. Stegosaurus lived during the Late Jurassic period from around
155-150 million years ago. It was the largest member of Stegosauridae yet to be discovered and would have to eat
constantly. However, the exact feeding strategy of Stegosaurus and Stegosaurs
in general is still not yet fully understood. The teeth of Stegosaurus are peg shaped and coupled with the wear on the teeth
and the restrictions regarding the jaws, suggests that Stegosaurus could only move its jaws up and down. Since the head of
Stegosaurus was small, pointed, and
stood at most three feet off the ground at all times the animal was most likely
a low level browser of soft material like shoots and fruits. According to an
analysis done on the jaw strength of Stegosaurus
done in 2010 the bite force of the animal was about half that of a common dog,
or about 140 Newton for the anterior, 183 Newton for the middle, and 270 for
the posterior teeth. This proves problematic to the understanding of how an
animal the size of Stegosaurus could
have a big enough food intake to survive and more research need to and is being
done on the subject. The one thing fossils have a hard time explaining is how
the animal that the fossils belonged to lived.
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| (Copyright for art belongs to; Geocities) |
The brain of Stegosaurus, although not quite
walnut-sized, was unusually small compared to the body mass and has the
smallest brain size to body mass of any other dinosaur species. This presented
a problem to the animal; how could it survive without a higher intelligence,
and giant bony billboards and four large sword-like spikes were the answer. Paleontologist
Matthew Mossbrucker discovered footprints of Adult, juvenile, and Hatchling
specimens in 2007 in the Morrison Formation, which suggests that Stegosaurs stayed together in small
groups, most likely for protection against predators. Another problem that Stegosaurs faced but fixed with armor
was its speed. Stegosaurus has
extraordinarily short front legs compared with the back legs and the femur was
longer than the tibia and fibula of the leg which would have made walking any
faster than six to seven kilometers an hour rather difficult. The other animals
that Stegosaurus shared its
environment with include, Allosaurus,
Ceratosaurus, Apatosaurus, Camarasaurus, and many others. Stegosaurus most likely fit into a niche
that none of the other organisms around it did, however that niche is not well
understood as stated previously. Although there is evidence that suggests
whenever an Allosaurus did attack a Stegosaurus it met its end, there is
also fossil evidence for the opposite suggesting that Allosaurus did, in fact, prey on Stegosaurus and were able to bring them down. There is a specimen
of Stegosaurus in which a U-shaped bite
mark is visible on one of the plates on the neck. This suggests a hunter/prey
relationship that went both ways in fatalities.
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| (Copyright for art belongs to; Geocities) |
Stegosaurus can be considered the
Rhinoceros or Hippopotamus of the Late Jurassic as it was both an herbivore and
highly dangerous to anything it perceived as a threat. Due to the excessive
deposits of this animal’s fossils, it has become the state fossil of Colorado
and a universal icon of the small group of famous dinosaurs of pop culture. Stegosaurus ruled whatever specifically
was its niche in its time period and then it and its relatives died out near
the end of the Jurassic leaving only fossils and footprints as a reminder of
its existence. However, Paleontologists have been able to, using the fossils
and a little bit of guesswork, roughly understand how this animal behaved, how
it lived, and how it died.
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| (Copyright for Stegosaurus belongs to; Gregory S. Paul) |
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| (Copyright belongs to; PrehistoricWildlife) |
Works
Cited
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Holtz, Thomas R. Jr. (2012)
Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of
All Ages, Winter 2011 Appendix.
Lambert D (1993). The Ultimate
Dinosaur Book. Dorling Kindersley, New York. pp. 110–29. ISBN 1-56458-304-X.
Carpenter K (1998). "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.
Carpenter K, Galton PM (2001).
"Othniel Charles Marsh and the Eight-Spiked Stegosaurus". In
Carpenter, Kenneth. The Armored Dinosaurs. Indiana University Press. pp.
76–102. ISBN 0-253-33964-
Pastino, Blake De. "Allosaurus
Died from Stegosaur Spike to the Crotch, Wyoming Fossil Shows." Western
Digs. Western Digs, 23 Oct. 2014. Web. 20 June 2015.
"Stegosaurus; Colorado State
Fossil." State Symbols USA. STATE SYMBOLS USA, n.d. Web. 21 June 2015.
Jacobson, Rebecca. "First
Steps of a Baby Stegosaurus, Captured in 3-D." PBS. PBS, 16 July 2014.
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