![](https://www.birdsoutsidemywindow.org/wp-content/uploads/2023/11/dinosaur_stegosaurus_stenops_life-reconstruction_wiki.jpg)
20 November 2023
For those who love dinosaurs, Stegosaurs are a recognizable favorite. These plant-eating armored animals wore rows of raised plates on their backs and spiky tails to protect them from the carnivores, especially the Allosaurus, a theropod ancestor of modern day birds.
When threatened, the Stegosaur swung its tail to batter its attacker with the spikes.
![](https://www.birdsoutsidemywindow.org/wp-content/uploads/2023/11/dinosaur_stegosaurus_tail_royal-belgian-institute_wiki.jpg)
This display at the Denver Museum of Nature and Science shows an Allosaur ready to bite a Stegosaur while two Stegosaur young run beneath her. Look closely in the background and you can see that the end of her tail — the spikes — are out of sight as they swing at the Alloasaur’s back.
![](https://www.birdsoutsidemywindow.org/wp-content/uploads/2023/11/dinosaur_bones_allosaurus_attacking_stegosaurus_family_denverNMH_wiki-1024x681.jpg)
When paleontologists were puzzled by a hole in this Allosaur vertebrae (at left) they figured out that a Stegosaur spike fits the hole (at right). Bone piercing bone in real time. Ouch!
![](https://www.birdsoutsidemywindow.org/wp-content/uploads/2023/11/dinosaur_allosaurus_vertebrae_with_stegosaurus_spike_holes_wiki.jpg)
The arrangement of the tail spikes had no name until “Kenneth Carpenter, then a paleontologist at the Denver Museum of Nature and Science, used the term when describing a fossil at the Society of Vertebrate Paleontology Annual Meeting in 1993.” — quote from Wikipedia.
The name came from a Far Side cartoon in 1982 when Gary Larson invented it as a joke. “Now, this end is called the thagomizer … after the late Thag Simmons.”
The name caught on and is now official.
A thagomizer is the distinctive arrangement of four spikes on the tails of stegosaurian dinosaurs. These spikes are believed to have been a defensive measure against predators.
— Wikipedia: Thagomizer account
The rest is history.
Watch out for that thagomizer!
(credits are in the captions. Tip of the hat to Jonathan Nadle who told me about the thagomizer.)