Thagomizer: Why Stegosaurus’ Spiky Tail Was Named After A Cartoon

Jul 13, 2020 2 comments

Humans and stegosaurus missed each other by more than 150 million years, but people have always wondered how difficult or terrifying life would have been if dinosaurs and humans co-existed. This premise is often explored humorously in cartoons and in movies. Cavemen and dinosaurs frequently featured in cartoonist Gary Larson’s The Far Side— a single-panel comic that ran for fifteen years during the 1980s and 90s. The Far Side was known for its surrealistic and dark humor based on uncomfortable social situations and improbable events, including aliens, talking cows, as well as human-dinosaur interaction.


Watercolor of a stegosaurus by Katrine Glazkova/

In 1982, Larson drew a comic depicting a prehistoric classroom. A caveman is giving a lecture to an audience of other cavemen. Before them is a large image of a stegosaurs’ tail. The professor points towards the spikes at the end of the tail and explains that they are called the “thagomizer”, after the late Thag Simmons.

Presumably, caveman Thag Simmons had gone too close to the stegosaurus and was clubbed to death by its spiky tail. Having learned a valuable lesson that it was best to avoid the tail of this particular animal, the other cavemen who witnessed the unfortunate incident decided to immortalize Thag’s name on the prehistoric animal’s anatomy.


Larson later joked that if there were confessionals for cartoonists, he would have gone to seek absolution: “Father, I have sinned—I have drawn dinosaurs and hominids together in the same cartoon.”

Of course, The Far Side is fiction, and no one named Thag Simmons was fatally wounded by an extinct animal. But the “thagomizer” itself is real.

It turns out that this arrangement of spikes at the tip of a stegosaurus’s tail had no formal name. A 2006 article in the New Scientist explains why that happened:

Paleontologists don't get many chances to name new bones. Evolution uses the same bones over and over again, altering their shape and purpose but preserving their basic nature, so anatomists simply use the same old terms to describe them. A humerus is a humerus, whether it's in a chicken wing, a walrus flipper, the massive front leg of a brachiosaurus or our own upper arm.

Only in a few animals do bones evolve into something different enough to earn their own distinct name, like the fearful-looking spikes at the end of a stegosaurus’ tail. Nevertheless, nobody had bothered to give an easy-to-remember name to the spikes, until Gary Larson came up with “thagomizer”. Larson, being a biologist, was aware of the deficiency.


Mounted Thagomizer at the Denver Museum of Nature and Science. Photo: Kevmin/Wikimedia Commons

In 1993, at the annual meeting of the Society of Vertebrate Paleontology at the Denver Museum of Nature and Science, paleontologist Ken Carpenter was making a presentation about a recently discovered stegosaurus skeleton. One of the spikes had apparently broken and healed, and there was a compelling evidence that the stegosaur had used its spiky tail as a weapon.

Carpenter remembered Larson’s cartoon that he read years ago, and he found the joke too good to pass. That was the first time anybody, outside Larson, had used the word “thagomizer” in a professional way.

Shortly after, the Dinosaur National Monument in Utah got the thagomizer label on its spikes, and James Orville Farlow of Indiana University included the term in his book The Complete Dinosaur. Smithsonian Institution's stegosaur fossil display also has the label thagomizer.

Since then, the word has become a semi-formal term for that part of the stegosaur’s anatomy.

Gary Larson also carries the honor of having two insect species named after him—a louse called "Strigiphilus garylarsoni" and a beetle named "Garylarsonus”.

Dale H. Clayton, who named Strigiphilus garylarsoni, wrote in a letter to Larson praising the cartoonist for “the enormous contribution that my colleagues and I feel you have made to biology through your cartoons.”

In his book The Prehistory of the Far Side, Larson quipped:

I considered this an extreme honor. Besides, I knew no one was going to write and ask to name a new species of swan after me. You have to grab these opportunities when they come along.

# The word: Thagomizer,
# Wikipedia,


  1. Good grief!
    When these brainiacs get together, they do some Bizarro things!
    What a load of banana oil!

  2. What makes it even more amazing is how the name Thag and the stegosaurus share roots in language: the word stegosaurus originally means something like “tiled lizard” in Greek (from στεγος - “roof” and σαύρα - “lizard”).
    The “stegos” part is related to a Sanskrit word स्थग “sthaga” (to hide of cover something, like a tiled roof or a thatch covers a house, or like a toga is a cloak to cover oneself) and to the Hindi word ठग “thag” (a thief or fraud) from which we have the word “thug”.


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