Product Code Database
Stegosauria is a group of Herbivore ornithischian that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere (North America, Europe and Asia), Africa and South America. Their geographical origins are unclear; the earliest unequivocal stegosaurian, Bashanosaurus primitivus, was found in the Bathonian Shaximiao Formation of China.
Stegosaurians were armored dinosaurs (). Originally, they did not differ much from more primitive members of that group, being small, low-slung, running animals protected by armored . An early evolutionary innovation was the development of spikes as defensive weapons. Later species, belonging to a subgroup called the Stegosauridae, became larger, and developed long hindlimbs that no longer allowed them to run. This increased the importance of active defence by the thagomizer, which could ward off even large predators because the tail was in a higher position, pointing horizontally to the rear from the broad pelvis. Stegosaurids had complex arrays of spikes and plates running along their backs, hips and tails.
Stegosauria includes two families, the primitive Huayangosauridae and the more derived Stegosauridae. The stegosaurids like all other stegosaurians were quadrupedal herbivores that exhibited the characteristic stegosaurian dorsal dermal plates. These large, thin, erect plates are thought to be aligned parasagittally from the neck to near the end of the tail. The end of the tail has pairs of spikes, sometimes referred to as a thagomizer. It may be that this is the only scientific term derived from a joke (in this case a The Far Side comic). Although defense, thermo-regulation and display have been theorized to be the possible functions of these dorsal plates, a study of the ontogenetic histology of the plates and spikes suggests that the plates serve different functions at different stages of the stegosaurids' life histories. The terminal spikes in the tail are thought to have been used in old adults, at least, as a weapon for defence. However, the function of stegosaurid plates and spikes, at different life stages, still remains a matter of great debate.
The first stegosaurian finds in the early 19th century were fragmentary. Better fossil material, of the genus Dacentrurus, was discovered in 1874 in England. Soon after, in 1877, the first nearly-complete skeleton was discovered in the United States. Professor Othniel Charles Marsh that year classified such specimens in the new genus Stegosaurus, from which the group acquired its name, and which is still by far the most famous stegosaurian. During the latter half of the twentieth century, many important Chinese finds were made, representing about half of the presently known diversity of stegosaurians.
In 1877, Arthur Lakes, a fossil hunter working for Professor Othniel Charles Marsh, in Wyoming excavated a fossil that Marsh the same year named Stegosaurus. At first, Marsh still entertained some incorrect notions about its morphology. He assumed that the plates formed a flat skin cover — hence the name, meaning "roof saurian" — and that the animal was bipedal with the spikes sticking out sideways from the rear of the skull. A succession of additional discoveries from the Como Bluff sites allowed a quick update of the presumed build. In 1882, Marsh was able to publish the first skeletal reconstruction of a stegosaur. Hereby, stegosaurians became much better known to the general public. The American finds at the time represented the bulk of known stegosaurian fossils, with about twenty skeletons collected.
The next important discovery was made when a German expedition to the Tendaguru, then part of German East Africa, from 1909 to 1912 excavated over a thousand bones of Kentrosaurus. The finds increased the known variability of the group, Kentrosaurus being rather small and having long rows of spikes on the hip and tail. From the 1950s onwards, the geology of China was systematically surveyed in detail and infrastructural works led to a vast increase of digging activities in that country. This resulted in a new wave of Chinese stegosaurian discoveries, starting with Chialingosaurus in 1957. Chinese finds of the 1970s and 1980s included Wuerhosaurus, Tuojiangosaurus, Chungkingosaurus, Huayangosaurus, Yingshanosaurus and Gigantspinosaurus. This increased the age range of good fossil stegosaurian material, as they represented the first relatively complete skeletons from the Middle Jurassic and the Early Cretaceous. Especially important was Huayangosaurus, which provided unique information about the early evolution of the group.
Towards the end of the twentieth century, the so-called Dinosaur Renaissance took place in which a vast increase in scientific attention was given to the Dinosauria. In 2007, Jiangjunosaurus was reported, the first Chinese dinosaur named since 1994. Nevertheless, European and North-American sites have become productive again during the 1990s, Miragaia having been found in the Lourinhã Formation in Portugal and a number of relatively complete Hesperosaurus skeletons having been excavated in Wyoming. Apart from the fossils per se, important new insights have been gained by applying the method of cladistics, allowing for the first time to exactly calculate stegosaurian evolutionary relationships.
Huayangosaurus had relatively long and slender arms. The forelimbs of later forms are very robust, with a massive humerus and ulna. The Carpal bones were reinforced by a fusion into two blocks, an ulnar and a radial. The front feet of stegosaurians are commonly depicted in art and in museum displays with fingers splayed out and slanted downward. However, in this position, most bones in the hand would be disarticulated. In reality, the hand bones of stegosaurians were arranged into vertical columns, with the main fingers, orientated outwards, forming a tube-like structure. This is similar to the hands of Sauropoda, and is also supported by evidence from stegosaurian footprints and fossils found in a lifelike pose. The long hindlimbs elevated the tail base, such that the tail pointed out behind the animal almost horizontally from that high position. While walking, the tail would not have sloped downwards as this would have impeded the function of the tail base retractor muscles, to pull the thighbones backwards. However, it has been suggested by Bob Bakker that stegosaurians could rear on their hind legs to reach higher layers of plants, the tail then being used as a "third leg". The mobility of the tail was increased by a reduction or absence of ossified tendons, that with many Ornithischia stiffen the hip region. Huayangosaurus still possessed them. In species that had short forelimbs, the relatively short torso towards the front curved strongly downwards. The dorsal vertebrae typically were very high, with very tall and transverse processes pointing obliquely upwards to almost the level of the neural spine top. Stegosaurian back vertebrae can easily be identified by this unique configuration. The tall neural arches often house deep ; enlarged canals in the sacral vertebrae have given rise to the incorrect notion of a "second brain". Despite the downwards curvature of the rump, the neck base was not very low and the head was held a considerable distance off the ground. The neck was flexible and moderately long. Huayangosaurus still had the probably original number of nine cervical vertebrae; Miragaia has an elongated neck with seventeen.
The stegosaurian shoulder girdle was very robust. In Huayangosaurus, the acromion, a process on the lower front edge of the shoulderblade, was moderately developed; the coracoid was about as wide as the lower end of the scapula, with which it formed the shoulder joint. Later forms tend to have a strongly expanded acromion, while the coracoid, largely attached to the acromion, no longer extends to the rear lower corner of the scapula.
The stegosaurian pelvis was originally moderately large, as shown by Huayangosaurus. Later species, however, convergent to the Ankylosauria developed very broad Pelvis, in which the formed wide horizontal plates with flaring front blades to allow for an enormous belly-gut. The ilia were attached to the sacral vertebrae via a sacral yoke formed by fused sacral ribs. Huayangosaurus still had rather long and obliquely oriented ischium and . In more derived species, these became more horizontal and shorter to the rear, while the front prepubic process lengthened.
Many basal stegosaurs like Gigantspinosaurus and Huayangosaurus have been discovered with parascapular spines, or spines emerging from the shoulder region. Among stegosaurids, only Kentrosaurus has been found with parascapular spines, which project posteriorly out of the lower part of the shoulder plates. These spines are long, rounded and comma-shaped in lateral view and have an enlarged base. Loricatosaurus was also believed to have a parascapular spine, but Maidment et al. (2008) observed that the discovered specimen, from which the spine is described, has a completely different morphology than the parascapular spine specimens of other stegosaurs. They suggest it may be a fragmentary tail spine instead. Stegosaurids also lack lateral scute rows that run longitudinally on either side of the trunk in Huayangosaurus and Ankylosauria, indicating yet another secondary loss of a plesiomorphic characters. However, the absence of lateral scutes as well as pre-maxillary teeth mentioned above are not specifically diagnostic of stegosaurids, since these features are also present in some other stegosaurians, whose phylogenetic relationships are unclear.
The discovery of an impression of the skin covering the dorsal plates has implications for all possible functions of stegosaurian plates. Christiansen and Tschopp (2010) found that the skin was smooth with long, parallel, shallow grooves indicating a keratinous structure covering the plates. The addition of beta-keratin, a strong protein, would indeed allow the plates to bear more weight, suggesting they may have been used for active defense. A keratinous covering would also allow greater surface area for the plates to be uses as a mating display structures, which could be potentially coloured like the beaks of modern birds. At the same time this finding implies that the use of plates for thermo-regulation may be less likely because the keratinous covering would make heat transfer from the bone highly ineffective.
Huayangosauridae (derived from Huayangosaurus, "Sichuan reptile") is a family of stegosaurian from the Jurassic of China. The group is defined as all taxa closer to the namesake genus Huayangosaurus than Stegosaurus, and was originally named as the family Huayangosaurinae by Dong Zhiming and colleagues in the description of Huayangosaurus. Huayangosaurinae was originally differentiated by the remaining taxa within Stegosauridae by the presence of teeth in the , an , and a . Huayangosaurinae, known from the Middle Jurassic of the Shaximiao Formation, was proposed to be intermediate between Scelidosaurinae and Stegosaurinae, suggesting that the origins of stegosaurs lay in Asia. Following phylogenetic analyses, Huayangosauridae was expanded to also include the taxon Chungkingosaurus, known from specimens from younger Late Jurassic deposits of the Shaximiao Formation. Huayangosauridae is either the sister taxon to all other stegosaurs, or close to the origin of the clade, with taxa like Gigantspinosaurus or Isaberrysaura outside the Stegosauridae-Huayangosauridae split. Huayangosauridae was formally defined in 2021 by Daniel Madzia and colleagues, who used the previous definitions of all taxa closer to Huayangosaurus taibaii than Stegosaurus stenops.
In 2017, Raven and Maidment published a comprehensive phylogenetic framework including most valid stegosaurian genera. Several subsequent publications expanded and corrected this matrix based on novel taxa and revised anatomical interpretations. In 2025, Sánchez-Fenollosa & Cobos compiled these variations and other observations into an updated and expanded dataset. The authors further coined the name Neostegosauria for the clade comprising the Dacentrurinae (including Kentrosaurus) and the Stegosaurinae. These results are displayed in the cladogram below:
A few million years later, during the Callovian-Oxfordian, from China much larger species are known, with long, "graviportal" (adapted for moving only in a slow manner on land due to a high body weight) hindlimbs: Chungkingosaurus, Chialingosaurus, Tuojiangosaurus and Gigantspinosaurus. Most of these are considered members of the derived Stegosauridae. Lexovisaurus and Loricatosaurus, stegosaurid finds from England and France of approximately equivalent age to the Chinese specimens, are likely the same taxon. During the Late Jurassic, stegosaurids seem to have experienced their greatest radiation. In Europe, Dacentrurus and the closely related Miragaia were present. While older finds had been limited to the northern continents, in this phase Gondwana was colonised also as shown by Kentrosaurus living in Africa. No unequivocal stegosaurian fossils have been reported from South-America, India, Madagascar, Australia, or Antarctica, though. A Late Jurassic Chinese stegosaurian is Jiangjunosaurus. The most derived Jurassic stegosaurians are known from North-America: Stegosaurus (perhaps several species thereof) and the somewhat older Hesperosaurus. Stegosaurus was quite large (some specimens indicate a length of at least seven metres), had high plates, no shoulder spine, and a short, deep rump.
From the Early Cretaceous, far fewer finds are known and it seems that the group had declined in diversity. Some fragmentary fossils have been described, such as Craterosaurus from England and Paranthodon from South Africa. Up until recently, the only substantial discoveries were those of Wuerhosaurus from Northern China, the exact age of which is highly uncertain More recent discoveries from Asia however would later begin to fill out the Early Cretaceous diversity of the group. Indeterminate stegosaurs are known from the Early Cretaceous of Siberia, including the Ilek Formation and Batylykh Formation. The youngest known definitive remains of stegosaurs are those of Mongolostegus from Mongolia, a stegosaurine from the Hekou Group of China, and Yanbeilong of the Zuoyun Formation of China, all of which date to the Aptian-Albian.
It has often been suggested that the decline in stegosaur diversity was part of a Jurassic-Cretaceous transition, where angiosperms become the dominant plants, causing a faunal turnover where new groups of herbivores evolved.Bakker, R.T., 1998, "Dinosaur mid-life crisis: the Jurassic-Cretaceous transition in Wyoming and Colorado", In: S.G. Lucas, J.I. Kirkland, & J.W. Estep (eds.) Lower and Middle Cretaceous Terrestrial Ecosystems; New Mexico Museum of Natural History and Science Bulletin, 14: 67-77 Although in general the case for such a causal relation is poorly supported by the data, stegosaurians are an exception in that their decline coincides with that of the Cycadophyta.Butler, R.J., Barrett, P.M., Kenrick, P. and Penn, M.G., 2009, "Diversity patterns amongst herbivorous dinosaurs and plants during the Cretaceous: implications for hypotheses of dinosaur/angiosperm co-evolution", Journal of Evolutionary Biology, 22: 446–459
Though Late Cretaceous stegosaurian fossils have been reported, these have mostly turned out to be misidentified. A well-known example is Dravidosaurus, known from Coniacian fossils found in India. Though originally thought to be stegosaurian, in 1991 these badly-eroded fossils were suggested to instead have been based on pelvis and hindlimb material,Chatterjee, S., and Rudra, D.K., 1996, "KT events in India: impact, rifting, volcanism and dinosaur extinction," in: Novas & Molnar, eds., Proceedings of the Gondwanan Dinosaur Symposium, Brisbane, Memoirs of the Queensland Museum, 39(3): iv + 489–731 : 489-532 and none of the fossils are demonstrably stegosaurian.Wilson, J. A., Barrett, P. M., & Carrano, M. T. (2011). An associated partial skeleton of Jainosaurus cf. septentrionalis (Dinosauria: Sauropoda) from the Late Cretaceous of Chhota Simla, central India. Palaeontology, 54(5), 981-998. The reinterpretation of Dravidosaurus as a plesiosaur wasn't accepted by Peter Galton and Upchurch (2004), who stated that the skull and plates of Dravidosaurus are certainly not plesiosaurian, and noted the need to redescribe the fossil material of Dravidosaurus. (2025). 9780520242098, University of California Press. ISBN 9780520242098 A purported stegosaurian dermal plate was reported from the latest Cretaceous (Maastrichtian) Kallamedu Formation (southern India); however, Galton & Ayyasami (2017) interpreted the specimen as a bone of a sauropod dinosaur. Nevertheless, the authors considered the survival of stegosaurians into the Maastrichtian to be possible, noting the presence of the stegosaurian ichnotaxon Deltapodus in the Maastrichtian Lameta Formation (western India).
The protective nature of dorsal plates has also been questioned in the past - Davitashvili (1961) noted that narrow dorsal location of the plates still left the sides vulnerable. Since the pattern of plates and spines vary between species, he suggested it could be important for intraspecific recognition and as a display for sexual selection. This is corroborated by Spassov's (1982) observations that the plates are arranged for maximum visible effect when viewed laterally during non-aggressive agonistic behaviour, as opposed to from a head-on aggressive stance.Spassov, N. B. (1982). The ‘‘bizarre’’ dorsal plates of stegosaurs: ethological approach. Comptes rendus de l’academie bulgare des Sciences, 35, 367–370.
Deltapodus is an ichnogenus attributed as stegosaurian prints, and are known across Europe, North Africa, and China. One Deltapodus footprint measures less than 6 cm in length and represents the smallest known stegosaurian track. Some tracks preserve exquisite scaly skin pattern.
Australia's 'Dinosaur Coast' in Broome, Western Australia includes tracks of several different thyreophoran track-makers. Of these, the ichnogenus Garbina (a Nyulnyulan word for 'shield') and Luluichnus (honours the late Paddy Roe, OAM who went by the name 'Lulu') have been considered registered by stegosaurs. Garbina includes the largest stegosaur tracks measuring 80 cm in length. Trackway data show Garbina track-makers were capable of bipedal and quadrupedal progression, suggesting an adaptation to facultative bipedalism amongst some stegosaurs.
While has no body fossil evidence currently known for stegosaurs, handprints from underground coal mines near Oakey, Queensland, resembling Garbina tracks suggests their occurrence in this country from at least the Middle to Upper Jurassic (Callovian–Tithonian). A single plaster cast of one of these handprints is in the collections of the Queensland Museum.
In 2001, a study of tail spikes by McWhinney et al.,
Kevin Padian, a paleontologist at the University of California, Berkeley, remarked that Saitta had misidentified features in his specimen's bone tissue sections and said "there's no evidence the animal has stopped growing". Paidan also expressed ethical concerns about the use of private specimens in the study.
Kentrosaurus, Dacentrurus and Stegosaurus are also suggested to have exhibited dimorphism in the form of three extra sacral ribs in the females.
Mallison (2010) suggested that Kentrosaurus may have used a tripodal stance on their hindlimbs and tail to double the foraging height from the general low browsing height under one metre for stegosaurids. This challenged the view that stegosaurs are primarily low vegetation feeders because of their small heads, short necks and short forelimbs, since the tripodal stance would also give them access to young trees and high bushes.
Another piece of evidence suggesting that some stegosaurids may have consumed more than just low vegetation was the discovery of the long-necked stegosaurid Miragaia longicollum. This dinosaur's neck has at least 17 cervical vertebrae achieved through the transformation of thoracic vertebrae into cervical vertebrae and possible lengthening of the centrum. This is more than most Sauropoda dinosaurs, which also achieved the elongation of the neck through similar mechanisms and had access to fodder higher off the ground.
Evidence from Sakha Republic suggests that Early Cretaceous stegosaurs living in high latitude environments were capable of palinal jaw motion and exhibited high rates of tooth replacement and short tooth formation time.
Trace fossils
Stegosaurian tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Cleveland-Lloyd quarry, which is located near Price, Utah."Walk and Don't Look Back: The Footprints; Stegosaurs" in Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pg. 238 Two years later, a new Ichnotaxon called Stegopodus was erected for another set of stegosaurian tracks which were found near Arches National Park, also in Utah. Unlike the first, this trackway preserved traces of the forefeet. Fossil remains indicate that stegosaurians have five digits on the forefeet and three weight-bearing digits on the hind feet. From this, scientists were able to predict the appearance of stegosaurian tracks in 1990, six years in advance of the first actual discovery of Morrison stegosaurian tracks. More trackways have been found since the erection of Stegopodus. None, however, have preserved traces of the front feet and stegosaurian traces remain rare.
Tail spikes
There has been debate about whether the spikes were used simply for display, as posited by Gilmore in 1914, or used as a weapon. Robert Bakker noted that it is likely that the stegosaur tail was much more flexible than those of other dinosaurs because it lacked ossified tendons, thus lending credence to the idea of the tail as a weapon. He also observed that Stegosaurus could have maneuvered its rear easily by keeping its large hindlimbs stationary and pushing off with its very powerfully muscled but short forelimbs, allowing it to swivel deftly to deal with attack. In 2010, analysis of a digitized model of Kentrosaurus showed that the tail could bring the thagomizer around to the sides of the dinosaur, possibly striking an attacker beside it.
McWhinney, L. A.; Rothschild, B. M. & Carpenter, K. (2025). 9780253339645, Indiana University Press. ISBN 9780253339645 showed a high incidence of trauma-related damage. This too supports the theory that the spikes were used in combat. There is also evidence for Stegosaurus defending itself, in the form of an Allosaurus tail vertebra with a partially healed puncture wound that fits a Stegosaurus tail spike. Stegosaurus stenops had four dermal spikes, each about long. Discoveries of articulated stegosaur armor show that, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted. Initially, Marsh described S. armatus as having eight spikes in its tail, unlike S. stenops. However, recent research re-examined this and concluded this species also had four.
Posture
A digital articulation and manipulation of digital scans of specimen material of Kentrosaurus inferred that stegosaurids may have used an erect limb posture, like that of most mammals, for habitual locomotion while using a sprawled crocodilian pose for defensive behavior. The sprawled pose would allow them to tolerate the large lateral forces used in swinging the spiked tail against predators as a clubbing device.
Sexual dimorphism
There have been several findings of possible sexual dimorphism in stegosaurids. Saitta (2015) presents evidence of two morphs of Hesperosaurus dorsal plates, with one morph having a wide, oval plate with a surface area 45% larger than the narrow, tall morph. Considering that dorsal plates most likely functioned as display structures and that the wide oval shape allowed a broad continuous display, Saitta assigns the wider morph with larger surface area as male.
Feeding
In order to explore the feeding habits of stegosaurids, Reichel (2010) created a 3-D model of Stegosaurus teeth using the software ZBrush. The model finds that the bite forces of Stegosaurus was significantly weaker than that of Labradors, wolves and humans. The finding suggests that these dinosaurs would be capable of breaking smaller branches and leaves with their teeth, but would not be able to bite through a thick object (12 mm or more in diameter). Parrish et al.'s (2004) description of Jurassic flora in the stegosaurid-rich Morrison Formation supports this finding. The flora during this time-period was dominated by seasonal small, fast-growing herbaceous plants, which stegosaurids could consume easily if Reichel's reconstruction is accurate.
External links
|
|
