Western North America and Europe (Portugal)
Length: 9 meters (30 feet)
Height: 4 meters (14 ft)
Weight: 7 tonnes (15,000 lb) as an adult
Trackways of Stegosaurus show that it was a herd animal with all ages of animals living together. This herd mentality would have offered protection from predators to the vulnerable, smaller juveniles. While a juvenile Stegosaurus possessed all the same physical features of an adult in a smaller scale, it is not possible that it would have been able to defend itself from Allosaurus, the apex predator of its time.
The tail spikes of Stegosaurus were certainly used for defence against Allosaurus! Fossil evidence shows a punctured Allosaurus tail vertebra into which a Stegosaurus tail spike fitted perfectly.