Stegosaurus emerges from fossil record

By Sara Thompson

Special to the Enterprise

Stegosaurus is one of the most recognized dinosaurs that has ever lived. Its shingle-like plates and pointy tail spikes make it seem very formidable. These large herbivores lived during the late Jurassic between 155-145 million years ago and are found in the upper Morrison Formation. This time also had other recognizable dinosaurs such as the long-necked sauropods of Apatosaurs, Diplodocus, and Brachiosaurus, but also predators like Ceratosaurus and Allosaurus, which likely preyed on Stegosaurus.

Stegosaurus had small, peg-like teeth and their jaw suggests they were capable of little more than an up and down movement. They had shorter forelimbs than hindlimbs, a short and stocky neck, and small head. Their limb arrangement would angle their head downward and tail upwards. They may have fed on lower vegetation, no higher than three feet high, but have their spiky tails raised up for defense if needed. Computer models suggest that they did not have a strong bite force and coupled with limited mobility of their jaw may have forced them to eat softer plant material such as moss, fruits, small twigs and limbs, and the leafy parts of plants. There has been no evidence of the use of gastroliths, or swallowed stones, to aid in digestion. Some scientists suggested that Stegosaurus may have reared up onto their hindlimbs to feed on taller vegetation. Their hindlimbs would be strong enough to sustain this position for short periods, but there is no definitive evidence that it happened.

The plates and spikes of Stegosaurus are one of the most distinguishable parts of the animal. The exact arrangement of the back plates is not exactly known, but the most accepted arrangement is two rows of alternating plates. The plates are not attached to the spine or other parts of the skeleton, so it is believed they were “floated” in the skin and flesh of the animal. The bony plates are smooth sided and have small grooves that likely supported capillaries. These would supply blood to a keratin sheath surrounding the bone and could have aided in thermoregulation of the animal or use in display for defense or attraction. The tail spikes of Stegosaurus were their best defense. Stegosaurus tails lacked ossified tendons suggesting they were more flexible than other dinosaur species. The tail spikes also show wear and damage that could be from use in defense. One of the best pieces of evidence of use in defense comes from an Allosaurus. An Allosaurus specimen was found with an injury to its tail vertebrae and a Stegosaurus tail spike fits perfectly into the wound. The tail spikes of Stegosaurus are often times called a thagomizer. This is not an official term by the scientific community but is widely used. It originated by cartoonist Gary Larson, who used the term in a The Far Side comic referencing the tail spike of Stegosaurus.

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