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Categories: StegosauriaHerbivoreUSAMorrisonLate Jurassic

HESPEROSAURUS

Pronunciation: hes-per-o-SOR-us
Meaning: Western lizard
Named by: Carpenter, et al. (2001)
Previous names: None known
First discovery: Wyoming, USA
Roar factor: 6/10

Hesperosaurus mjosi

Hesperosaurus is a spike-tailed stegosaurine dinosaur hailing from the Late Jurassic Morrison Formation of Wyoming, and is the oldest and most primitive stegosaur known from North America.
Well, that was the original diognosis. It had only been named for seven years before Susannah Maidement swung her axe in the general direction of Stegosauria and trimmed its numbers somewhat, assigning Hesperosaurus to Stegosaurus as Stegosaurus mjosi, but not every paleontologist agrees.

Aside from wider than high alternating plates on its back and a deeper, broader skull, its remains were found very low in the Morrison Formation which makes it older than any known species of Stegosaurus. It appears to be closer to Dacentrurus.
(Mjos's Western Lizard) Etymology
Hesperosaurus is derived from the Greek "hespero" (western), in reference to its discovery in the Western United States, and "sauros" (lizard). The species epithet, mjosi, honors Ronald G. Mjos ("mūs") who collected and prepared the specimen.
Discovery
The fossils of Hesperosaurus were discovered in Buffalo Quarry at S.B. Smith Ranch, stratigraphic zone 1 of the Morrison Formation, Johnson County, Wyoming, USA, by Patrick McSherry in June 1985. The holotype (HMNH 001) is a skull and partial skeleton, minus the legs.
References
K. Carpenter, C.A. Miles and K. Cloward (2001) "A New Primitive Stegosaur from the Morrison Formation, Wyoming" in K. Carpenter's "The Armored Dinosaurs". /uk.
• Susannah C.R. Maidment, David B. Norman, Paul M.Barrett and Paul Upchurch (2008) "Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)".
Estimations
Timeline: Vital Stats:
Era: Mesozoic Est. Max. Length: 5 meters
Period: Late Jurassic Est. Max. Height: ?
Timespan: 156-151 million years ago Est. Max. Weight: 700 kg
Age: Kimmeridgian Diet: Herbivorous
             
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