The Hesperosaurus is a stegosaurian dinosaur from the Upper Jurassic, approximately 150 million years ago. It is compared to the Stegosaurus more often that experts sometimes refer to the two as male and female counterparts of the same species. This, however, is not the case as the Hesperosaurus and Stegosaurus dinosaurs differ not only in body structure but in their way of living too. 

Key facts

Hesperosaurus pronunciationhes-per-oh-sore-us
What does Hesperosaurus mean?Western lizard
Dinosaur typeAnkylosauria
On the menuHerbivorous
Length21 feet (6.5 meters)
Height7 feet (2 meters)
WeightAbout 7700 lbs (3.5 tons)
Life expectancyUnknown
Legs used to get aroundQuadruped
Estimated top speedUnknown
When they livedUpper Jurassic era 154-142 million years ago
Where they have been found?USA

When & Where

In 1985, fossil discoverer, Patrick McSherry unearthed the remains of a stegosaur in Johnson County, Wyoming. With the help of other paleontologists, he secured the specimen and classified it as a Stegosaurus. It was not until 2001 that Kenneth Carpenter, Clifford Miles, and Karen Cloward described and named the remains Hesperosaurus mjosi. The naming was in accordance with its place of discovery; the western United States of America. 

Size & Weight

The Hesperosaurus was a huge dinosaur that measured up to 6.5 meters in length and weighed 3.5 metric tons in body mass. Fully grown Hesperosaurus are estimated to have weighed a staggering 5 metric tons. Although scientists often grouped the Stegosaurus and Hesperosaurus as one, the Hesperosaurus was relatively small and had fewer plates on its back.  

Mobility & Diet

Like its cousin Stegosaurus, the Hesperosaurus was a herbivorous dinosaur. It is believed to have lived in grassland areas and fed on low-lying vegetation. The skull structure and teeth formation of the Hesperosaurus indicates that it could only have been able to feed on plant matter. 

Interesting Points

  • The specific name commemorates Mjos who partook in the process of collecting and preparing the holotype. Mjos also had a cast of the Hesperosaurus made. 
  • The Hesperosaurus had a thagomizer at the end of its tail which paleontologists have described as a means of protection.
  • Its mounted skeleton in the North American Museum of Ancient Life is almost complete, with only the limbs missing.
  • It is considered one of the most famous Stegosaurus.

Featured Image Credit: Nobu Tamura, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons