Tuesday, August 30, 2011

Stegosaurus: Search for the Truth (2 of 3)

Marsh made other errors about the Stegosaurus that still plague paleontologists today.  He named various species of the Stegosaurus family based on incomplete fossils or mixed-up ones.  Several species that he named were juveniles of a single species.  Meanwhile, other early naturalists mistook some fossils from other species for Stegosaurus’ ones.  Today, scientists are sorting out the various species, and have placed the taxonomy of the Stegosaurus family under extensive review.

Another fallacy that Marsh made was to claim that the Stegosaurus had a second brain in His butt.  Two reasons for this was the large size of the animal, and the cavity found in His spinal region.  Because the Stegosaurus had a large body to small brain ratio, people reasoned that the dinosaur must have had something to control His legs and tail.  The second brain theory would fit for a dinosaur with a walnut-sized brain.  However, the cavity in the hip area is something common to sauropods in general.

Moreover, the small size of the brain of the Stegosaurus became something applied to other dinosaurs.  Since this dinosaur was one of the earliest to be found, people reasoned that the other dinosaurs must have had small brains as well.  The conclusion became that all dinosaurs were stupid, and went extinct as a result.  The truth of the matter was that the Stegosaurus had a very narrow head with a beak, while the other dinosaurs had bigger brains.

How the Stegosaurus walked has been also prone to a plethora of theories.  Since the Stegosaurus has an unusual posture of an inverted “U”, this animal’s forelimbs are shorter than the hind limbs.  Skeletons on display showed an animal with sprawling limbs and a dragging tail.  However, the limbs were directly under the body allowing the dinosaur’s neck to be more erect.  Furthermore, the tail was held high off the ground for balance.

The symbol of the wacky theories endured by the Stegosaurus is the thagomizer.  The tail spikes of this dinosaur were named after a “Far Side” (Gary Larson) cartoon. The cartoon had a professor caveman explaining to his cavemen students that the end of the tail was named “for the late Thag Simmons.”  Paleontologists, in a rare moment of humor, decided to call this dinosaur’s spikes: “thagomizers”.  When first depicted, the Stegosaurus had eight spikes that stood upright.  Later fossils discoveries showed that the dinosaur only had four horizontal spikes.

At first, naturalists believed that the tail was for show.  However, several fossils of Allosaurus, a known predator, had puncture wounds from a Stegosaurus’ tail.  Therefore, this dinosaur had used His tail for defense in combat, and not for display.


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