Sophie’s back, from neck to tail
Sophie is the first Stegosaurus found with its plates still in order along its back. In 2015 Susannah Maidment, Charlotte Brassey and Paul Barrett measured every one they could.
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
How many plates?
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 Sophie has 19 plates and four tail spikes, the most complete set ever discovered. Natural History Museum press release: World’s most complete Stegosaurus goes on show, 2014
One of Sophie’s 19 plates is a cast. Natural History Museum: Secrets of the Stegosaurus, 2014 Before Sophie, the 1914 study of Stegosaurus guessed there were probably 20 plates. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE
Small at the neck, huge over the hips
Her four front plates, on the neck, are almost identical in shape and only about 10 to 13 cm tall. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE Sophie’s biggest plate is number 13, about 785 mm tall, though part of it is plaster. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE
From the chart you can see the pattern: small plates on the neck, the biggest over the hips and the base of the tail, then smaller again towards the spikes.
Which side?
The plates stood upright, alternating on either side of the spine. Natural History Museum: Stegosaurus (Dino Directory) Even with Sophie, scientists can’t tell which way each plate leaned, left or right. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE
The spikes
Sophie’s tail spikes are 34 to 38 cm long. Maidment, Brassey & Barrett (2015), The postcranial skeleton of an exceptionally complete individual of Stegosaurus stenops, PLOS ONE The spiky tail is nicknamed the “thagomizer”, after a Far Side cartoon by Gary Larson about “the late Thag Simmons”. Smithsonian Magazine: Watch out for that thagomizer!, 2011
What were they 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)
Nobody knows for sure. The evidence for each idea is on the open questions page.
The drawing is our own diagram, not a tracing of the fossil. Plate heights and lengths are drawn to one scale from the published measurements. The spacing between plates, the lean of each plate and the body outline are simplified. Real plates are thin sheets of bone with grooves, and in life they were probably covered in keratin.