Kentrosaurus: Jurassic Stegosaur

Kentrosaurus was a small stegosaur that lived during the Jurassic Period, about 156 to 150 million years ago. It reached lengths of up to 17 feet, weighed two tons, and was clearly a herbivore judging from its relatives and the nature of its skull. Fossils of kentrosaurus have been discovered in Tanzania, Africa.

Unlike its relative, the well-known stegosaurus, kentrosaurus had both armored plates and bony spikes running down its back. Stegosaurus had rows of diamond-shaped plated running all the way down the length of its back, while kentrosaurus only had these plates on half of its back (until the back legs). These plates were not actually attached to the vertebrate, so they might not have been very effective defense measures. Instead they might have been used for temperature regulation like the sail of pelycosaurs, or as courtship displays during mating season. The imprint of blood vessels in fossil records gives evidence for the former contention. The two rows of spikes that were present on stegosaurus' tail were present in around seven rows down kentrosaurus' back. These foot-long spikes allowed the animal a potent defensive measure on its tail which it could swing with grim effect, but also a deterrent to predators trying to attack its back. This could have allowed kentrosaurus to graze on low-lying plants fairly safely, as many predators would avoid such potentially dangerous prey.

Kentrosaurus had a very small head, and like stegosaurus most likely had a very small brain to accompany that miniscule cranium. There is evidence to suggest that the olfactory region of the brain was well-developed, so the dinosaur would be able to smell approaching danger. With its advanced defenses, kentrosaurus would not have needed to know much more than how to eat, smell, and avoid predators. Its back legs were twice as long as its front legs, which suggests that kentrosaurus had a bipedal ancestor, and simply evolved sturdier front legs to support its increasing bulk over the evolutionary timeline. These powerful hind legs might have allowed this herbivore to stand up briefly on two legs in order to reach choice vegetation higher than the animal would be on all fours. In any case, the short length of its thigh bone relative to the overall size of the leg suggests that it was a very slow-moving herbivore which would have relied on body defenses rather than speed to elude predators. At the end of its mouth, kentrosaurus possessed a toothless beak which would allow it to snip off vegetation and grind it with simple cheek teeth inside its mouth.

It is unclear how kentrosaurus became extinct, though it was probably due to gradual competition from other herbivores, or the evolution of larger and more effective predators. It did not live past the Jurassic Period.