Stegosaurus
Stegosaurus is a genus of herbivorous four-legged armored dinosaurs from the Late Jurassic, characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. Fossils of the genus have been found in the western United States and in Portugal, where they are found in Kimmeridgian- to Tithonian-aged strata, dating to between 155 and 145 million years ago. Of the species that have been classified in the upper Morrison Formation of the western US, only three are universally recognized: S. stenops, S. ungulatus and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs such as Apatosaurus, Diplodocus, Camarasaurus and Allosaurus, the latter of which may have preyed on it.
They were large, heavily built, herbivorous quadrupeds with rounded backs, short fore limbs, long hind limbs, and tails held high in the air. Due to their distinctive combination of broad, upright plates and tail tipped with spikes, Stegosaurus is one of the most recognizable kinds of dinosaurs. The function of this array of plates and spikes has been the subject of much speculation among scientists. Today, it is generally agreed that their spiked tails were most likely used for defense against predators, while their plates may have been used primarily for display, and secondarily for thermoregulatory functions. Stegosaurus had a relatively low brain-to-body mass ratio. It had a short neck and a small head, meaning it most likely ate low-lying bushes and shrubs. One species, Stegosaurus ungulatus, is one of the largest known of all the stegosaurians, with the largest known specimens measuring about long and weighing over.
Stegosaurus remains were first identified during the "Bone Wars" by Othniel Charles Marsh at Dinosaur Ridge National Landmark. The first known skeletons were fragmentary and the bones were scattered, and it would be many years before the true appearance of these animals, including their posture and plate arrangement, became well understood. Despite its popularity in books and film, mounted skeletons of Stegosaurus did not become a staple of major natural history museums until the mid-20th century, and many museums have had to assemble composite displays from several different specimens due to a lack of complete skeletons. Stegosaurus is one of the better-known dinosaurs and has been featured in film, on postal stamps, and in many other types of media.
History and naming
Bone Wars and ''Stegosaurus armatus''
Stegosaurus, one of the many dinosaurs described in the Bone Wars, was first collected by Arthur Lakes and consisted of several caudal vertebrae, a dermal plate, and several additional postcranial elements that were collected north of Morrison, Colorado, at Lakes' YPM Quarry 5. These first, fragmented bones became the holotype of Stegosaurus armatus when Yale paleontologist Othniel Charles Marsh described them in 1877. Marsh initially believed the remains were from an aquatic turtle-like animal, and the basis for its scientific name, 'roof lizard' was due to his early belief that the plates lay flat over the animal's back, overlapping like the shingles on a roof. Though several more complete specimens have been attributed to Stegosaurus armatus, preparation of the bones and analysis has discovered that this type specimen is actually dubious, which is not an ideal situation for the type species of a well-known genus like Stegosaurus. Because of this, the International Commission on Zoological Nomenclature decided to replace the type species with the more well known species Stegosaurus stenops. Marsh also incorrectly referred several fossils to S. armatus, including the dentary and teeth of the sauropod Diplodocus and putting sauropod limb bones and an Allosaurus tibia under YPM 1850.On the other side of the Bone Wars, Edward Drinker Cope named Hypsirhophus discurus as another stegosaurian based on fragmentary fossils from Cope's Quarry 3 near the "Cope's Nipple" site in Garden Park, Colorado, in 1878. Many later researchers have considered Hypsirhophus to be a synonym of Stegosaurus, though Peter Galton suggested that it is distinct based on differences in the vertebrae. F. F. Hubbell, a collector for Cope, also found a partial Stegosaurus skeleton while digging at Como Bluff in 1877 or '78 that are now part of the Stegosaurus mount at the American Museum of Natural History.
Arthur Lakes made another discovery later in 1879 at Como Bluff in Albany County, Wyoming, the site also dating to the Upper Jurassic of the Morrison Formation, when he found several large Stegosaurus fossils in August of that year. The majority of the fossils came from Quarry 13, including the type specimen of Stegosaurus ungulatus, which was collected by Lakes and William Harlow Reed the same year and named by Marsh. The specimen was one of many found at the quarry, the specimen consisting of a partial skull, several vertebrae, an ischium, partial limbs, several plates, and four thagomizers, though eight thagomizers were referred based on a specimen preserved alongside the type. The type specimen also preserved the pes, which was the namesake of the species, meaning "hoofed roofed lizard". In 1881, he named a third species Stegosaurus "affinis", based only on a hip bone, though the fossil has since been lost and the species declared a nomen nudum. Later in 1887, Marsh described two more species of Stegosaurus from Como Bluff, Stegosaurus duplex, based on a partial vertebral column, partial pelvis, and partial left hindlimb from Reed's Quarry 11, though the species is now seen as synonymous with Stegosaurus ungulatus. The other, Stegosaurus sulcatus, was named based on a left forelimb, scapula, left femur, several vertebrae, and several plates and dermal armor elements collected in 1883. Stegosaurus sulcatus most notably preserves a large spike that has been speculated to have been a shoulder spike that is used to diagnose the species.
The greatest Stegosaurus discovery came in 1885 with the discovery of a nearly complete, articulated skeleton of a subadult that included previously undiscovered elements like a complete skull, throat ossicles, and articulated plates. Marshall P. Felch collected the skeleton throughout 1885 and 1886 from Morrison Formation strata at his quarry in Garden Park, a town near Cañon City, Colorado. The skeleton was expertly unearthed by Felch, who first divided the skeleton into labeled blocks and prepared them separately. The skeleton was shipped to Marsh in 1887, who named it Stegosaurus stenops that year. Though it had not yet been completely prepared, the nearly complete and articulated type specimen of Stegosaurus stenops allowed Marsh to complete the first attempt at a reconstructed Stegosaurus skeleton. This first reconstruction, of S. ungulatus with missing parts filled in from S. stenops'', was published by Marsh in 1891.
Early skeletal mounts and plate interpretation
The skeleton of S. stenops has since been deposited at the National Museum of Natural History in Washington D. C., where it has been on display since 1915. Another mount was made for the NMNH in the form of a mounted composite skeleton consisting of several specimens referred to S. stenops that were collected at Quarry 13 at Como Bluff in 1887, the most complete being USNM 6531. The type specimen of S. ungulatus was incorporated into the first ever mounted skeleton of a stegosaur at the Peabody Museum of Natural History in 1910 by Richard Swann Lull. It was initially mounted with paired plates set wide, above the base of the ribs, but was remounted in 1924 with two staggered rows of plates along the midline of the back. Additional specimens recovered from the same quarry by the United States National Museum of Natural History, including tail vertebrae and an additional large plate, belong to the same individual as YPM 1853.The next species of Stegosaurus to be named was S. marshi by Frederick Lucas in 1901. Lucas reclassified this species in the new genus Hoplitosaurus later that year. Lucas also re-examined the issue of the life appearance of Stegosaurus, coming to the conclusion that the plates were arranged in pairs in two rows along the back, arranged above the bases of the ribs. Lucas commissioned Charles R. Knight to produce a life restoration of S. ungulatus based on his new interpretation. However, the following year, Lucas wrote that he now believed the plates were probably attached in staggered rows. In 1910, Richard Swann Lull wrote that the alternating pattern seen in S. stenops was probably due to shifting of the skeleton after death. He led the construction of the first ever Stegosaurus skeletal mount at the Peabody Museum of Natural History, which was depicted with paired plates. In 1914, Charles Gilmore argued against Lull's interpretation, noting that several specimens of S. stenops, including the now-completely prepared holotype, preserved the plates in alternating rows near the peak of the back, and that there was no evidence of the plates having shifted relative to the body during fossilization. Gilmore and Lucas' interpretation became the generally accepted standard, and Lull's mount at the Peabody Museum was changed to reflect this in 1924.
Though considered one of the most distinctive types of dinosaur, Stegosaurus displays were missing from a majority of museums during the first half of the 20th century, due largely to the disarticulated nature of most fossil specimens. Until 1918, the only mounted skeleton of Stegosaurus in the world was O. C. Marsh's type specimen of S. ungulatus at the Peabody Museum of Natural History, which was put on display in 1910. However, this mount was dismantled in 1917 when the old Peabody Museum building was demolished. This historically significant specimen was re-mounted ahead of the opening of the new Peabody Museum building in 1925. 1918 saw the completion of the second Stegosaurus mount, and the first depicting S. stenops. This mount was created under the direction of Charles Gilmore at the U.S. National Museum of Natural History. It was a composite of several skeletons, primarily USNM 6531, with proportions designed to closely follow the S. stenops type specimen, which had been on display in relief nearby since 1918. The aging mount was dismantled in 2003 and replaced with a cast in an updated pose in 2004. A third mounted skeleton of Stegosaurus, referred to S. stenops, was put on display at the American Museum of Natural History in 1932. Mounted under the direction of Charles J. Long, the American Museum mount was a composite consisting of partial remains filled in with replicas based on other specimens. In his article about the new mount for the museum's journal, Barnum Brown described the popular misconception that the Stegosaurus had a "second brain" in its hips. Another composite mount, using specimens referred to S. ungulatus collected from Dinosaur National Monument between 1920 and 1922, was put on display at the Carnegie Museum of Natural History in 1940.