How many spikes does a stegosaurus have

Depending on the species, a Stegosaurus might have between one and four pairs of spikes—Marsh did not consider the possibility that spikes might have been lost in some specimens or that extra spikes might be found with others. If a bone or specimen looked different enough from what was already known, then it deserved to be separated as a new species.

The practice created persistent headaches for generations of paleontologists after Marsh. Frustratingly, Marsh did not provide details about why he thought each species had differing numbers of spikes.

It seems that he simply took what was found in the field at face value, even though several specimens with only four tail spikes were known to him by the time of his reconstruction. The eight-spiked Stegosaurus may have simply been a product of confusion and standard practices at the time, but there is no evidence that this dinosaur had any more or less than four spikes. Scientists began informally calling the spikes thagomizers after a pop culture reference in , when a "Far Side" cartoon showed a group of cavemen calling the sharp spikes thagomizers "after the late Thag Simmons," according to New Scientist.

Experts think these spikes were used for defense against predators because of two lines of evidence. For one thing, about 10 percent of spikes found are damaged at the tip, Carpenter said. Additionally, scientists have found allosaur fossils Stegosaurus 's main predator with puncture wounds from thagomizers.

Stegosaurus ' long skull was pointed and narrow. It had an unusual head-down posture because it had forelimbs that were short in relation to its hind legs. This leg-length imbalance suggests the dinosaur couldn't move very fast, because the stride of its back legs would have overtaken its front legs. Stegosaurus was an herbivore, as its toothless beak and small teeth were not designed to eat flesh and its jaw was not very flexible.

Interestingly, unlike other herbivorous, beaked dinosaurs including Triceratops and the duck-billed Hadrosaurids , Stegosaurus did not have strong jaws and grinding teeth. Instead, its jaws likely only allowed up and down movements, and its teeth were rounded and peglike. It also had cheeks, which gave it room to chew and store more food than many other of dinosaurs. As a result of its short neck and small head, it most likely ate low-lying bushes and shrubs and other vegetation, including ferns, mosses, cycads, fruits, conifers, horsetails and even fallen fruit.

Some scientists believe Stegosaurus could have stood on its hind legs to reach some taller plants, but this idea is debated. Stegosaurus had a formidable tail. Studded with four long spikes, this dinosaur's business end would have given Allosaurus and other Jurassic predators plenty of incentive to keep moving.

But do we have any evidence that Stegosaurus really used its tail this way? Among paleontologists, the four-spiked tail of Stegosaurus is called a " thagomizer. Whether Stegosaurus —and similarly equipped armored dinosaurs—used their thagomizers as weapons has been a minor point of scientific debate.

The spikes certainly look like weapons, but that, by itself, isn't sufficient to tell what their function was. Paleontologists needed some kind of evidence of direct interaction between predator and prey, and in paleontologists Kenneth Carpenter, Frank Sanders, Lorrie McWhitnney and Lowell Wood reported just that.

Proceedings of the United States National Museum 49, Hayashi, S. Ontogenetic histology of Stegosaurus plates and spikes. Palaeontology 55, Hone, D. Journal of Zoology , Main, R. The evolution and function of thyreophoran dinosaur scutes: implications for plate function in stegosaurs. Paleobiology 31, The views expressed are those of the author s and are not necessarily those of Scientific American.

Darren Naish is a science writer, technical editor and palaeozoologist affiliated with the University of Southampton, UK. He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish. He has been blogging at Tetrapod Zoology since Check out the Tet Zoo podcast at tetzoo.

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