Short answers, pulled from the story.
Stegosaurus is a genus of extinct herbivorous four-legged armored dinosaur from the Late Jurassic. It is recognizable for a double row of kite-shaped upright plates along its rounded back and two pairs of long spikes near the end of its tail. It had short fore limbs, longer hind limbs, a small head, and a short neck.
Stegosaurus lived in the Late Jurassic, roughly between 155 and 145 million years ago. Fossils have been found in the western United States, in the Morrison Formation, and in Portugal, in Kimmeridgian to Tithonian aged strata. It lived alongside dinosaurs such as Apatosaurus, Diplodocus, Camarasaurus, and Allosaurus.
Yale paleontologist Othniel Charles Marsh described and named the first Stegosaurus in 1877, during the rivalry known as the Bone Wars. The original fragmented bones were collected north of Morrison, Colorado, by Arthur Lakes and H.C. Beckwith. The name means roof lizard, because Marsh first thought the plates lay flat over the back like roof shingles.
The spiked tail was most likely used for defense against predators, supported by trauma damage in 9.8 percent of examined specimens and an Allosaurus vertebra punctured by a fitting spike. The plates may have been used mainly for display and secondarily for thermoregulation, since they carried blood vessels and showed extreme vascularization. The function of the plates remains debated.
Stegosaurus stenops reached about 6.5 meters in length and Stegosaurus ungulatus about 7 meters, with some large individuals reaching 7.5 meters and over 5 metric tons. Despite weighing over 4.5 metric tons, its braincase was no larger than a dog's, with a brain of no more than 80 grams, proportionally the smallest of any dinosaur known in Marsh's time.
The Stegosaurus skeleton nicknamed Apex sold for 44.6 million dollars at a Sotheby's auction in New York City on the 17th of July 2024, the most ever paid for a fossil. The nearly complete 27-foot specimen was discovered in 2022 on private land in Colorado. Its sale to a private owner renewed concern among researchers who want important fossils permanently curated at formal institutions.