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Stegosaurus
In 1877, Othniel Charles Marsh examined a fragmentary collection of bones from Morrison, Colorado, and concluded he was looking at an aquatic turtle-like creature. The fossil included a single dermal plate that led him to name the animal Stegosaurus armatus, meaning armored roof lizard, because he believed the plates lay flat over the back like shingles on a roof. This initial misinterpretation would haunt the scientific understanding of the creature for decades, as the true posture and function of these structures remained a mystery until the mid-20th century. The first bones were so incomplete that Marsh could not even determine if the animal walked on two legs or four, leading to early sketches that depicted the creature as bipedal with a long neck and plates arranged along its tail. It would take nearly two decades of additional discoveries and the fierce competition of the Bone Wars to begin piecing together the true, quadrupedal reality of this massive herbivore.
The Bone Wars Discovery
The story of Stegosaurus is inextricably linked to the violent rivalry between Othniel Charles Marsh and Edward Drinker Cope, a period known as the Bone Wars. While Marsh was busy describing the first Stegosaurus remains from Dinosaur Ridge, Cope was racing to find his own specimens, naming a stegosaurian Hypsirhophus discurus from Garden Park, Colorado, in 1878. The race to the west was fueled by collectors like Arthur Lakes, who found the first Stegosaurus fossils in 1877, and Marshall P. Felch, who made the most significant discovery of the era. In 1885, Felch unearthed a nearly complete, articulated skeleton of a subadult at his quarry in Garden Park, including a complete skull and throat ossicles that had never been seen before. Marsh named this specimen Stegosaurus stenops, meaning narrow-faced roof lizard, and used it to create the first reconstructed skeleton in 1891. This specimen, now housed at the National Museum of Natural History in Washington D.C., allowed scientists to finally understand the animal's proportions, though the initial mount was still flawed by the lack of complete knowledge regarding the plate arrangement.
The Plate Arrangement Debate
For the first half of the 20th century, the scientific community was divided on how the plates were arranged on the Stegosaurus back. Early reconstructions by Charles R. Knight and Frederic Lucas depicted the plates in pairs, set wide above the base of the ribs, a view that dominated museum displays until 1924. However, Charles Gilmore argued against this interpretation, noting that articulated specimens from Quarry 13 at Como Bluff showed the plates in alternating rows along the midline of the back. By the early 1960s, the staggered double row became the accepted standard, largely because fossils like the type specimen of S. stenops preserved the plates in this specific chiral arrangement. This arrangement is so distinct that a specimen must be distinguished from its hypothetical mirror-image form, as no two plates of the same size and shape have been found for an individual. The debate was further complicated by the discovery of skin impressions on related species like Hesperosaurus, which showed the plates were covered in keratinous sheaths, adding a layer of complexity to how they might have functioned in life.
Othniel Charles Marsh examined the first Stegosaurus bones in 1877 and named the species Stegosaurus armatus. The initial discovery included a single dermal plate that led Marsh to believe the animal was an aquatic turtle-like creature. This initial misinterpretation would haunt the scientific understanding of the creature for decades.
Who discovered the first Stegosaurus fossils and where?
Arthur Lakes found the first Stegosaurus fossils in 1877 at Dinosaur Ridge in Morrison, Colorado. Marshall P. Felch later made the most significant discovery of the era by unearthing a nearly complete skeleton at his quarry in Garden Park, Colorado, in 1885. These discoveries were part of the fierce competition known as the Bone Wars between Othniel Charles Marsh and Edward Drinker Cope.
How were Stegosaurus plates arranged on the back?
The plates were arranged in alternating rows along the midline of the back rather than in pairs. This staggered double row became the accepted standard by the early 1960s after fossils like the type specimen of Stegosaurus stenops preserved the plates in this specific chiral arrangement. The plates were likely used primarily for display and secondarily for thermoregulation.
Did Stegosaurus have a second brain in its hips?
No, Stegosaurus did not have a second brain in its hips. The large canal in the hip region of the spinal cord contained a glycogen body that facilitated the supply of glycogen to the animal's nervous system. This space likely functioned as a balance organ or a reservoir of compounds to support the nervous system.
What is the significance of the Stegosaurus fossil named Sophie?
Sophie is the best-preserved Stegosaurus specimen ever found and was discovered by Bob Simon in 2003 at a quarry on the Red Canyon Ranch near Shell, Wyoming. The skeleton was 85% intact and contained 360 bones, providing scientists with unprecedented detail on the animal's anatomy. The specimen went on display in December 2014 at the Natural History Museum in London.
How did Stegosaurus use its tail spikes?
The tail of Stegosaurus was tipped with four dermal spikes known as a thagomizer and was likely a formidable weapon. A study by McWhinney et al. found that 9.8% of Stegosaurus specimens examined had injuries to their tail spikes. The tail was likely much more flexible than that of other dinosaurs, lacking ossified tendons, which allowed the animal to swivel deftly to deal with attacks.
One of the most enduring misconceptions about Stegosaurus is the existence of a second brain located in its hips. Soon after describing the animal, Marsh noted a large canal in the hip region of the spinal cord, which could have accommodated a structure up to 20 times larger than the famously small brain. This led to the influential idea that the dinosaur had a second brain to control reflexes in the rear portion of the body, giving it a temporary boost when under threat from predators. Modern science has since debunked this theory, revealing that the sacro-lumbar expansion is not unique to stegosaurs and is also present in birds. In birds, this space contains what is called the glycogen body, a structure whose function is postulated to facilitate the supply of glycogen to the animal's nervous system. The space likely functioned as a balance organ or a reservoir of compounds to support the nervous system, rather than serving as a secondary center of intelligence.
Sophie and the Modern Era
The modern understanding of Stegosaurus was revolutionized by the discovery of Sophie, the best-preserved specimen ever found. Discovered by Bob Simon in 2003 at a quarry on the Red Canyon Ranch near Shell, Wyoming, the skeleton was 85% intact and contained 360 bones. The Natural History Museum in London purchased the specimen, which was given the official designation NHMUK PV R36730 and re-nicknamed Sophie after the landowner's daughter. This young adult, measuring 5.8 meters in length and 2.9 meters tall, went on display in December 2014 and provided scientists with unprecedented detail on the animal's anatomy. Even more recently, in July 2024, a nearly complete 27-foot skeleton nicknamed Apex fetched $44.6 million at a Sotheby's auction, the most ever paid for a fossil. These discoveries have clarified the position of plates and spikes, the size of throat ossicles, and the growth patterns of the species, moving the field beyond the fragmentary remains that had defined research for over a century.
Weapons and Defense
The tail of Stegosaurus, tipped with four dermal spikes known as a thagomizer, was likely a formidable weapon rather than just a display feature. While early researchers like Gilmore in 1914 suggested the spikes were used for display, more recent studies have shown a high incidence of trauma-related damage to the tail spikes. A study by McWhinney et al. found that 9.8% of Stegosaurus specimens examined had injuries to their tail spikes, and a punctured tail vertebra of an Allosaurus fits perfectly with a Stegosaurus spike, showing that the spike entered at an angle from below. The tail was likely much more flexible than that of other dinosaurs, lacking ossified tendons, which would have allowed the animal to swivel deftly to deal with attacks. The plates, meanwhile, were probably used primarily for display and secondarily for thermoregulation, with blood vessels running through grooves that could have helped control body temperature or create a colorful warning signal.
Life in the Morrison
Stegosaurus lived in the semiarid environment of the Morrison Formation, which featured distinct wet and dry seasons and flat floodplains. The landscape was a mix of river-lining forests of conifers and tree ferns, and fern savannas with occasional trees like the Araucaria-like conifer Brachyphyllum. The animal lived alongside a diverse array of creatures, including theropods like Allosaurus, Saurophaganax, and Torvosaurus, as well as sauropods such as Brontosaurus, Diplodocus, and Camarasaurus. Stegosaurus may have preferred drier settings than these other dinosaurs, foraging at most one meter above the ground on low-growing foliage like mosses, ferns, and cycads. Evidence from footprints discovered by Matthew Mossbrucker suggests that Stegosaurus lived and traveled in multiple-age herds, with tracks showing four or five baby stegosaurs moving in the same direction alongside adult tracks.
Cultural Iconography
Despite its scientific complexity, Stegosaurus became one of the most recognizable dinosaurs in popular culture, appearing in film, cartoons, and children's toys. The earliest popular image was an engraving by Auguste-Michel Jobin in 1884, which depicted the dinosaur as bipedal with plates along the tail. This image was later corrected by Charles R. Knight, whose 1901 painting of a staggered double row of plates became the basis for the stop-motion puppet used in the 1933 film King Kong. The first mounted skeleton of a stegosaur was put on display at the Peabody Museum in 1910, and by the mid-20th century, Stegosaurus had become a staple of major natural history museums. The creature's distinctive appearance has ensured its place in the public imagination, from the 1904 Louisiana Purchase Exposition to modern museum displays, making it one of the better-known dinosaurs in history.