Stegosaurus, plate by plate.
Nineteen plates nobody can fully explain, four tail spikes that really did hit Allosaurus, a brain the size of a plum and no second brain at all. Meet Sophie, the world’s most complete Stegosaurus, and the questions scientists are still arguing about. Every fact traced to a museum or a peer-reviewed paper.
The short version
Stegosaurus means “roof lizard”. Natural History Museum: Stegosaurus (Dino Directory) Stegosaurus was named by Othniel Charles Marsh in 1877. Natural History Museum: Stegosaurus (Dino Directory)
The Natural History Museum dates it to the Late Jurassic, 152 to 145 million years ago. Natural History Museum: Stegosaurus (Dino Directory) · checked 27 Oct 2026 Stegosaurus was a large, slow-moving plant eater. Natural History Museum: Stegosaurus (Dino Directory)
Stegosaurus lived about 150 million years ago and T. rex about 70 million years ago, so we live closer in time to T. rex than Stegosaurus did. American Museum of Natural History: Apex Stegosaurus fossil and “11 Questions About Stegosaurus”
Despite being so famous, well-preserved Stegosaurus fossils are surprisingly rare: most specimens are less than half a skeleton. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE
Sophie’s back, plate by plate
Eighteen plates and four spikes were found in place. A gap above the tail suggests one more plate washed away, so the full set was probably 19 plates and four spikes. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE Drag the slider to walk from neck to tail.
Plate 1
- Tallest point
- 103 mm
- Longest point
- 45 mm
Plate 2
- Tallest point
- not measured
- Longest point
- 48 mm
- Note
- top third missing (poorly preserved)
Plate 3
- Tallest point
- 112 mm
- Longest point
- 54 mm
Plate 4
- Tallest point
- 126 mm
- Longest point
- 57 mm
Plate 5
- Tallest point
- 107 mm
- Longest point
- 167 mm
Plate 6
- Tallest point
- 127 mm
- Longest point
- 181 mm
Plate 7
- Tallest point
- 258 mm
- Longest point
- 200 mm
Plate 8
- Tallest point
- 352 mm
- Longest point
- 280 mm
- Note
- as preserved
Plate 9
- Tallest point
- 463 mm
- Longest point
- 368 mm
Plate 10
- Tallest point
- 490 mm
- Longest point
- 465 mm
Plate 11
- Tallest point
- 445 mm
- Longest point
- 447 mm
Plate 12
- Tallest point
- 535 mm
- Longest point
- 460 mm
Plate 13
- Tallest point
- 785 mm
- Longest point
- not measured
- Note
- largest; partly plaster
Plate 14
- Tallest point
- not measured
- Longest point
- not measured
- Note
- not measured in the table
Plate 15
- Tallest point
- 536 mm
- Longest point
- 440 mm
Plate 16
- Tallest point
- 382 mm
- Longest point
- not measured
- Note
- height as reconstructed
Plate 17
- Tallest point
- not measured
- Longest point
- not measured
- Note
- poorly preserved
Plate 18
- Tallest point
- 175 mm
- Longest point
- 193 mm
- Note
- height as reconstructed
Plate 19
- Tallest point
- not measured
- Longest point
- not measured
- Note
- poorly preserved
Measurements are maxima from Maidment, Brassey and Barrett’s 2015 description of Sophie, tables 4 and 5. Plate 14 has no row in the table, and plates 2, 17 and 19 were too poorly preserved to measure fully. The spacing of the plates and the body outline in the drawing are our own schematic. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE
Start exploring
Plates, spikes, head & brainPlates in the skin, the thagomizer, tiny teeth and a plum-sized brain.
How it livedFerns and cycads, a few miles an hour, and fights with Allosaurus.
Sophie, Apex & the type specimenThe world’s most complete Stegosaurus, a $44.6 million sale and a skeleton still in its death pose.
Discovery & old mistakesA giant turtle, wrist spikes, eight spikes and a second brain. All wrong.
Open questionsPlates, males and females, herds, bite force and how many species. Still argued about.
Its world & relativesThe Morrison Formation, its neighbours and its plated cousins.
Tile images are credited on their pages and on the credits page.
What were the plates for?
Scientists are not exactly sure what the plates were for. Ideas include warning off predators, recognising their own kind, and controlling body temperature. Natural History Museum: Stegosaurus (Dino Directory) An AMNH curator says display, to mates or rivals, is the most likely function. American Museum of Natural History: Apex Stegosaurus fossil and “11 Questions About Stegosaurus”
The spikes were weapons
An Allosaurus tail bone from Utah’s Cleveland-Lloyd Quarry has a hole about 1.5 inches square that a Stegosaurus spike fits. The bone had started to heal. Smithsonian Magazine: Watch out for that thagomizer!, 2011 More on the plates and spikes page.
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Stegosaurus printables
Fact-checked PDFs in A4 and US Letter.
Stegosaurus Science Detective Pack
Five real cases to solve like a palaeontologist: what were the plates for, did the tail spikes really hit Allosaurus, was it male or female, how heavy was Sophie, and how many species are there? Evidence cards and answer keys
Stegosaurus Plates, Spikes & Sophie Worksheets
Label the Stegosaurus, graph Sophie’s real plate measurements, spike maths, weight estimates, a timeline and a true or false quiz, with an answer key
Plated & Armoured Dinosaurs ID Cards
Twelve double-sided cards: eight plated and armoured dinosaurs, from Stegosaurus to Ankylosaurus, plus four Morrison Formation neighbours, with a timeline game and a Name That Stegosaur game
Stegosaurus Activity & Colouring Pack
Colouring scenes, a maze, dot-to-dot, spot the difference and puzzles for ages 4 to 9
Stegosaurus Facts Poster Set
Six fact-checked posters, from the plum-sized brain to Sophie, the world’s most complete Stegosaurus
Stegosaurus Quiz & Word Puzzles Pack
A crossword, code breaker, word search, fill-the-gap facts, true or false and a 16-question quiz, with answer keys
Best valueThe Complete Stegosaurus Printables Bundle
All six packs plus a guide, A4 and US Letter, in one download.