Stegosaurus stenops is one of the most easily recognized dinosaurs, with the raised flat plates on its back and prominent spikes at the end of its tail. S. stenops lived in the Late Jurassic, approximately 157 to 145 million years ago. It was a large herbivorous land animal, reaching 6.5 m long and weighing approximately 3500 kg. Though Stegosaurus have been traditionally interpreted with a quadrupedal gait (on all fours), it is possible that they could have slowly walked on its hind legs, or reared back on its hind legs for feeding (1). S. stenops is well-represented in the fossil record compared to other Stegosaurus species. Both adults and juveniles have been found, including a complete adult articulated skeleton, with bones preserved in the same position as when the animal was alive. Many more partial skeletons have been discovered, providing many samples for paleontologists to study (2).
Stegosaurus stenops lived in the Late Jurassic, approximately 157 to 145 years ago. It has been found in Colorado in the lower Morrison formation. S. stenops lived in semiarid floodplain prairies and riverine forests. A wide variety of dinosaurs and other animals inhabited this habitat as well, such as the large theropods Allosaurus and Torvosaurus. Allosaurus in particular has been implicated as a possible predator of S. stenops, andAllosaurus bones have been discovered with puncture marks fromStegosaurus tail spikes. Other herbivorous dinosaurs in this ecosystem included Apatosaurus, Camptosaurus, and Camarasaurus (1).
The plant life in this ecosystem was very different from those seen in similar environments today. S. stenops lived before the evolution of flowering plants. Many of our modern dominant species would not have been present at this time, such as grasses and some tree groups. Insect varieties were comparable to modern times, but mammals were reduced in size, niche occupation, and development. The mammals of this time period laid eggs and did not grow larger than a rat (2).
Stegosaurus stenops is part of Stegosauridae, a group that contains other dinosaurs with plated or horned backs, such as Kentrosaurus. According to recent phylogenetic analysis, S. stenops and other members of its genus are more derived members of this group, closely related to Wuerhosaurus and Hesperosaurus (1).
Within the Stegosaurus genus, there are several different species. Stegosaurus armatus was the first stegosaur discovered, named by Othniel Charles Marsh in 1877 (2). Including S. stenops and S. armatus, there are currently four Stegosaurus species recognized. More species were originally described in the first rush of stegosaur identification, but they are no longer considered valid (3).
Stegosaurus stenops, like other stegosaurs, was an herbivore. It had ridged leaf-shaped teeth, though the beaked front of its jaws was toothless. S. stenops likely preferred browsing at low to medium levels (1). Analysis on the bite force of Stegosaurus finds that it had a weak bite compared to humans, dogs, and wolves. However, its biting power still would have been sufficient to bite through leaves and small branches up to 12 mm in diameter. It likely fed upon small and fast-growing plants (2). Stegosaurus tooth wear patterns indicate that it could have chewed its food, but the infrequency of tooth wear demonstrates that this was probably only an occasional behavior (3). Stegosaurus also likely used its beak in feeding, using it to chop weaker vegetation (4). Though Stegosaurus spent most of its time in a four-legged quadrupedal stance, some paleontologists think that it could have raised itself onto its back legs, supported by its tail. In this manner, it could have potentially browsed at much higher levels (5).
One of the most recognizable features of Stegosaurus, is the two rows of flattened triangular plates running from the neck to the tip of the tail. The function of these plates has been a matter of debate in the paleontology community for decades. The structure of the plates suggests that they were covered with a layer of skin enriched by many blood vessels. These blood vessels may have helped Stegosaurus regulate its heat through its plates. The plates could have released heat for cooling, and absorbed heat from the sun to warm Stegosaurus (2).
Other paleontologists think that the plates served as protection from predators. The plates even could have helped protect the skin of Stegosaurus from being damaged by abrasion from coarse vegetation. A third possibility is that the plates were used for display, either to make Stegosaurus look larger and more intimidating to predators, or to impress potential mates in courtship rituals. It is possible that all of these uses were valid (1).
A more recent interpretation of plate function describes a different form of display. It is possible that the heavy vascularization of the plates could have allowed them to “blush.” They could have used this to quickly add red color to their plates during a threat display (2).
Paleontologists have also debated on the arrangement of the plates on the back of Stegosaurus. The plates were originally thought to lie flat on the back like shingles, but it is now understood that they were raised on edge. Some reconstruct Stegosaurus with paired sets of plates, while others think they had a staggered pattern (1).
The tip of the tail of Stegosaurus stenops bears four large spikes. These spikes measure between 60-90 cm in length. Often portrayed vertically, more recent discoveries suggest that these spikes may have projected horizontally instead (1). Originally, paleontologists wondered whether the spikes might be used in display (2). Now it is understood that the spikes were most likely weapons. Many dinosaurs have ossified tendons, tendons which have been infiltrated by bone for support, strengthening and stiffening their tail. Stegosaurus did not have these hardened tendons, leaving their tail with a greater degree of flexibility (3). Additionally, the tail spikes demonstrate a high level of trauma-related damage, such as might be caused by heavy impact (4). The discovery of an Allosaurus vertebra with a puncture wound matching the shape of a Stegosaurus spine seems to further support this use (5).
