October 21. Stegosaurus

Drawing by Marsh (USGS, public domain). This is an inaccurate depiction – a single row of back plates (rather than two) and too many tail spikes (should be two pairs).

We really can’t go through the Jurassic without talking about stegosaurus, arguably one of the most recognizable dinosaurs. The first specimen of stegosaurus was found near Morrison, Colorado, in 1877, by O.C. Marsh during his “bone war” with Edward Cope. Its remarkably small brain was noticed immediately – something like 2½ ounces for a 10-ton body, and modern reconstructions depict a creature that may have moved slowly but that probably carried its spiked tail high and might have wielded it like a weapon. 

Stegosaurus, whose name means “roofed” or “covered lizard,” in reference to the bony plates on its back, was a herbivore that grew to 30 feet long. It couldn’t lift its head very high, so it probably grazed on ground cover or short bushes.

For all its fame, only about 80 individuals are represented in fossils. Most are from the Morrison Formation of western United States, but in 2006 one was found in Portugal. Ancestral stegosaurids – not the genus Stegosaurus – are known from the United States, China, England, Germany, and France, but Stegosaurus itself appears to have had a limited distribution in both time and space. There are some Cretaceous specimens that some researchers have attributed to Stegosaurus, but this is not generally accepted, and as far as we can tell with certainty, Stegosaurus was only on the scene for about 5 million years, from about 150 to 155 million years ago.

If you see an image of Stegosaurus juxtaposed with Triceratops or Tyrannosaurus rex, be very suspicious. That image is off by about 80 million years.

—Richard I. Gibson

Kung-fu Stegosaur

Drawing by Marsh (USGS, public domain). This is an inaccurate depiction – a single row of back plates (rather than two) and too many tail spikes (should be two pairs).