Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, Africa, South America and Asia Their geographical origins are unclear; the earliest unequivocal stegosaurian, Huayangosaurus taibaii, lived in China.
Stegosaurians were armored dinosaurs (thyreophorans). Originally, they did not differ much from more primitive members of that group, being small, low-slung, running animals protected by armored scutes. An early evolutionary innovation was the development of tail spikes, or "thagomizers", 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. Their necks became longer and their small heads became narrow, able to selectively bite off the best parts of cycads with their beaks. When these plant types declined in diversity, so did the stegosaurians, which became extinct during the first half of the Cretaceous period.
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.
|Mounted skeleton of Stegosaurus stenops, Natural History Museum, London|
Stegosaurians had characteristic small, long, flat, narrow heads and a horn-covered beak or rhamphotheca, which covered the front of the snout (two premaxillaries) and lower jaw (a single predentary) bones. Similar structures are seen in turtles and birds. Apart from Huayangosaurus, stegosaurians subsequently lost all premaxillary teeth within the upper beak. Huayangosaurus still had seven per side. The upper and lower jaws are equipped with rows of small teeth. Later species have a vertical bone plate covering the outer side of the lower jaw teeth. The structure of the upper jaw, with a low ridge above, and running parallel to, the tooth row, indicates the presence of a fleshy cheek. In stegosaurians, the typical archosaurian skull opening, the antorbital fenestra in front of the eye socket, is small, sometimes reduced to a narrow horizontal slit.
All stegosaurians are quadrupedal, with hoof-like toes on all four limbs. All stegosaurians after Huayangosaurus have forelimbs much shorter than their hindlimbs. Their hindlimbs are long and straight, designed to carry the weight of the animal while stepping. The condyles of the lower thighbone are short from the front to the rear. This would have limited the supported rotation of the knee joint, making running impossible. Huayangosaurus had a thighbone like a running animal. The upper leg was always longer than the lower leg.
Huayangosaurus had relatively long and slender arms. The forelimbs of later forms are very robust, with a massive humerus and ulna. The wrist 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 sauropod dinosaurs, 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 Robert Thomas 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 neural arches 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 neural canals; 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. Ossified sternal plates have never been found with Stegosauria and perhaps the sternum was completely absent.
The stegosaurian pelvis was originally moderately large, as shown by Huayangosaurus. Later species, however, convergent to the Ankylosauria developed very broad pelves, in which the iliac bones 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 ischia and pubic bones. In more derived species, these became more horizontal and shorter to the rear, while the front prepubic process lengthened.
Like all Thyreophora, stegosaurians were protected by bony scutes that were not part of the skeleton proper but skin ossifications instead: the so-called osteoderms. Huayangosaurus had several types. On its neck, back, and tail were two rows of paired small vertical plates and spikes. On the rear of the tail, pairs of spikes were present forming the so-called "thagomizer", a defensive weapon. The very tail end bore a small club. Each flank had a row of smaller osteoderms, culminating in a long shoulder spine in front, curving to the rear. Later forms show very variable configurations, combining plates of various shape and size on the neck and front torso with spikes more to the rear of the animal. They seem to have lost the tail club and the flank rows are apparently absent also, with the exception of the shoulder spine, still shown by Kentrosaurus and extremely developed, as its name indicates, in Gigantspinosaurus. As far as is known, all forms possessed some sort of thagomizer, though these are rarely preserved articulated allowing to establish the exact arrangement. A fossil of Chungkingosaurus sp. has been reported with three pairs of spikes pointing outwards and a fourth pair pointing to the rear. The most derived species, like Stegosaurus, Hesperosaurus and Wuerhosaurus, have very large and flat back plates. To discern them from the smaller plates, which are intermediate to spines in having a thickened central section, these latter are sometimes called 'splates'. Stegosaurus plates are so large that it has been suggested that they were not arranged in paired but alternated rows or even formed a single overlapping midline row. With Stegosaurus fossils also ossicles have been found in the throat region, bony skin discs that protected the lower neck. Apart from protection, suggested functions of the osteoderms include display, species recognition and thermoregulation.
Stegosaurian tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Cleveland-Lloyd quarry, which is located near Price, Utah. Two years later, a new ichnogenus 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.
Like the spikes and shields of ankylosaurs, the bony plates and spines of stegosaurians evolved from the low-keeled osteoderms characteristic of basal thyreophorans. One such described genus, Scelidosaurus, is proposed to be morphologically close to the last common ancestor of the clade uniting stegosaurians and ankylosaurians, the Eurypoda. Galton (2019) interpreted plates of an armored dinosaur from the Lower Jurassic (Sinemurian-Pliensbachian) Lower Kota Formation of India as fossils of a member of Ankylosauria; the author argued that this finding indicates a probable early Early Jurassic origin for both Ankylosauria and its sister group Stegosauria. Footprints attributed to the ichnotaxon Deltapodus brodricki from the Middle Jurassic (Aalenian) of England represent the oldest probable record of stegosaurians reported so far. Outside that, there are assigned fossils to stegosauria from the Toarcian: the specimen "IVPP V.219", a chimaera with bones of the sauropod Sanpasaurus is know from the Maanshan Member of the Ziliujing Formation. The perhaps most basal known stegosaurian, the four-metre-long Huayangosaurus, is still close to Scelidosaurus in build, with a higher and shorter skull, a short neck, a low torso, long slender forelimbs, short hindlimbs, large condyles on the thighbone, a narrow pelvis, long ischial and pubic shafts, and a relatively long tail. Its small tail club might be a eurypodan synapomorphy. Huayangosaurus lived during the Bathonian stage of the Middle Jurassic, about 166 million years ago.
A few million years later, during the Callovian-Oxfordian, from China much larger species are known, with long, "graviportal", i.e., a type 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. The only more substantial discoveries are those of Wuerhosaurus, the exact age of which is highly uncertain. In the autumn of 2016, the teeth and tail spikes of stegosaurs were found in a Russian ravine that was once part of an Early Cretaceous river. The remains of these stegosaurs and other dinosaurs in the area were all miniature, implying that either large amounts of baby dinosaurs spent the first stage in their lives here, or that the area was home to dwarf dinosaurs. Several Russian scientists also theorize that the remains of these stegosaurs, as well as the remains of allosaurids in the same area, could imply that the area could have once been a "refugium", where these Jurassic dinosaurs managed to survive into the Cretaceous period.
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. 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.
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 plesiosaurian pelvis and hindlimb material, and none of the fossils are demonstrably stegosaurian. The reinterpretation of Dravidosaurus as a plesiosaur wasn't accepted by 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. 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 Stegosauria was originally named as an order within Reptilia by O.C. Marsh in 1877, although today they are generally treated as an infraorder or suborder — or more often an unranked clade — within the Thyreophora, the armored dinosaurs. It includes in modern usage the families Huayangosauridae and Stegosauridae, named in 1982 and 1880 respectively.
The Huayangosauridae were an early group of stegosaurians that lived during the early to middle Jurassic Period. They were smaller than later stegosaurians and had shorter and higher skulls. Huayangosauridae is undefined. Currently, the only unequivocal genus included is the type genus Huayangosaurus of China. The poorly known remains of Regnosaurus from the early Cretaceous of England, however, indicate that it too could be a member — or at least a basal stegosaurian. They consist of a lower jaw that is very similar to that of the former genus.
The vast majority of stegosaurian dinosaurs thus far recovered belong to the Stegosauridae, which lived in the later part of the Jurassic and early Cretaceous, and which were defined by Paul Sereno as all stegosaurians more closely related to Stegosaurus than to Huayangosaurus. They include per definition the well-known Stegosaurus. This group is widespread, with members across the Northern Hemisphere, Africa and possibly South America.
The first exact clade definition of Stegosauria was given by Peter Malcolm Galton in 1997: all thyreophoran Ornithischia more closely related to Stegosaurus than to Ankylosaurus. Thus defined, the Stegosauria are by definition the sister group of the Ankylosauria within the Eurypoda.
Kenneth Carpenter of the Denver Museum of Nature and Science published a preliminary phyletic tree of stegosaurians, in the 2001 description of Hesperosaurus. An updated phylogeny was published by Mateus et al. (2009), which is shown below.
Alternately, in 2017 Raven and Maidment published a new phylogenetic analysis, including almost every known stegosaurian genus:
To date, several genera from China bearing names have been proposed but not formally described, including "Changdusaurus". Until formal descriptions are published, these genera are regarded as nomina nuda. Yingshanosaurus, for a long time considered a nomen nudum, was described in 1994.
The first known discovery of a possible stegosaurian was probably made in the early nineteenth century in England. It consisted of a lower jaw fragment and was in 1848 named Regnosaurus. In 1845, in the area of the present state of South Africa, remains were discovered that much later would be named Paranthodon. In 1874, from England, other remains were named Craterosaurus was named. All three taxa were based on fragmentary material and were not recognised as possible stegosaurians until the twentieth century. They gave no reason to suspect the existence of a new distinctive group of dinosaurs.
In 1874, extensive remains, the first partial stegosaurian skeleton known, were uncovered in England of what was clearly a large herbivore equipped with spikes. They were named Omosaurus by Richard Owen in 1875. Later, this name was shown to be preoccupied by the phytosaur Omosaurus and the stegosaurian was renamed Dacentrurus. Other English nineteenth century and early twentieth century finds would be assigned to Omosaurus; later they would, together with French fossils, be partly renamed Lexovisaurus and Loricatosaurus. None of these specimens was complete though, and even together they could not have provided a good understanding of stegosaurian build. Owen e.g., initially assumed that the spikes were placed on the wrists. However, very soon after the discovery of Omosaurus, American finds would fully compensate for this.
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.
After 1912, Western researchers for a long time failed to identify any new stegosaurians, scientific interest in dinosaurs as whole being rather limited during the middle of the twentieth century. 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. As part of this development, the rate of dinosaurian discoveries quickly picked up. However, this has not resulted in a peak of stegosaurian finds, partly because most new sites are from the Cretaceous, when stegosaurian diversity had declined. 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 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.
The following timeline shows the date of descriptions for valid stegosaurian genera beginning in 1824, when the first non-avian dinosaur, Megalosaurus, was formally described. The fossils themselves were found earlier; in the case of Loricatosaurus e.g. there is a gap of 107 years between the discovery and the naming of the genus.
In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian age succeeds the Bajocian age and precedes the Callovian age.Chialingosaurus
Chialingosaurus (meaning "Chialing Lizard") is a genus of herbivorous stegosaurian dinosaur similar to Kentrosaurus from the Upper Shaximiao Formation, Late Jurassic beds in Sichuan Province in China. Its age makes it one of the oldest species of stegosaurs, living about 160 million years ago. Since it was an herbivore, scientists think that Chialingosaurus probably ate ferns and cycads, which were plentiful during the period when Chialingosaurus was alive.Chungkingosaurus
Chungkingosaurus, meaning "Chongqing Lizard", is a genus of herbivorous dinosaur from the Late Jurassic Upper Shaximiao Formation in what is now China. It is a member of the Stegosauria.Como Bluff
Como Bluff is a long ridge extending east-west, located between the towns of Rock River and Medicine Bow, Wyoming. The ridge is an anticline, formed as a result of compressional geological folding. Three geological formations, the Sundance, the Morrison, and the Cloverly Formations, containing fossil remains from the Late Jurassic of the Mesozoic Era are exposed. Nineteenth century paleontologists discovered many well-preserved specimens of dinosaurs, as well as mammals, turtles, crocodilians, and fish from the Morrison Formation. Because of this, Como Bluff is considered to be one of the major sites for the early discovery of dinosaur remains. Among the species discovered is the only known specimen of Coelurus. Significant discoveries were made in 22 different areas scattered along the entire length of the ridge. It is included on the National Register of Historic Places as well as the National Natural Landmark list.Craterosaurus
Craterosaurus (meaning krater reptile or bowl reptile) was a genus of stegosaurid dinosaur. It lived during the Early Cretaceous (Valanginian to Barremian stages) around 145-136 million years ago. Its fossils were found in the Woburn Sands Formation of England. Craterosaurus may actually be a junior synonym of Regnosaurus, but only one fossil, a partial vertebra, was recovered.
The type (and only known) species is Craterosaurus pottonensis, described in 1874 by Harry Seeley. The specific name refers to the Potton bonebed. Seeley mistook the fossil, holotype SMC B.28814, for the base of a cranium. Franz Nopcsa in 1912 correctly identified it as the front part of a neural arch. Craterosaurus was placed in Stegosauria by Galton, although subsequent authors did not recognize Craterosaurus as a distinct, valid taxon.Dacentrurus
Dacentrurus (meaning "tail full of points"), originally known as Omosaurus, was a large stegosaur of the Late Jurassic Period (154 - 150 mya) of Europe. Its type species, Omosaurus armatus, was named in 1875, based on a skeleton found in the Kimmeridge Clay of England. In 1902 the genus was renamed Dacentrurus because the name Omosaurus had already been used for a crocodylian. After 1875, half a dozen other species would be named but perhaps only Dacentrurus armatus is valid.
Finds of this animal have been limited and much of its appearance is uncertain. It was a heavily built quadrupedal herbivore, adorned with plates and spikes.Gigantspinosaurus
Gigantspinosaurus (meaning "giant-spined lizard") is a genus of herbivorous ornithischian dinosaur from the Late Jurassic. It was a stegosaur found in China.Huayangosaurus
Huayangosaurus is a genus of stegosaurian dinosaur from the Middle Jurassic of China. The name derives from "Huayang" (華陽), an alternate name for Sichuan (the province where it was discovered), and "saurus", meaning "lizard". It lived during the Bathonian to Callovian stages, around 165 million years ago, some 20 million years before its famous relative, Stegosaurus appeared in North America. At only 4.5 metres long, it was also much smaller than its famous cousin. Found in the Lower Shaximiao Formation, Huayangosaurus shared the local Middle Jurassic landscape with the sauropods Shunosaurus, Datousaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the carnivorous Gasosaurus. It was found in Huayang in China.Isaberrysaura
Isaberrysaura is a genus of ornithischian dinosaur from the Early Jurassic Los Molles Formation of Patagonia, Argentina. The genus contains a single species, I. mollensis, described by Salgado et al. in 2017 from a single specimen. Although initially classified as a basal neornithischian, subsequent analysis has allied it with the Stegosauria; the morphology of its skull resembles those of other members of the group.Lexovisaurus
Lexovisaurus is a genus of stegosaur from mid-to-Late Jurassic Europe, 164.7 mya. Fossils of limb bones and armor fragments have been found in middle to late Jurassic-aged strata of England and France.Loricatosaurus
Loricatosaurus (meaning "armored lizard") is a dinosaur of Stegosauridae family from Callovian-age (Middle Jurassic) rocks of England and France.Lusitanosaurus
Lusitanosaurus (meaning "Portuguese lizard") is a genus of basal thyreophoran dinosaur from the Early Jurassic of Portugal.
The genus was first described by Albert-Félix de Lapparent and Georges Zbyszewski in 1957. The type species is Lusitanosaurus liasicus. The generic name is derived from Lusitania, the ancient Latin name for the region. The specific name refers to the Lias.
The holotype is part of the collection of the Museu de História Natural da Universidade de Lisboa. The exact location of the find and the date of collection are unknown, which makes a correct geological dating difficult, but it can be inferred from the matrix rock that it has been discovered near São Pedro de Moel, in strata from the Sinemurian (Early Jurassic). This would make it the oldest known dinosaur from Portugal. The fossil consists of a single partial left maxilla, an upper jaw bone, with seven teeth.
Originally assigned to the Stegosauria by de Lapparent, Lusitanosaurus is today considered a basal member of the Thyreophora, perhaps belonging to the Scelidosauridae. Some authors consider it a nomen dubium.Paranthodon
Paranthodon ( pə-RAN-thə-don) is a genus of stegosaurian dinosaur that lived in what is now South Africa during the Early Cretaceous, between 139 and 131 million years ago. Discovered in 1845, it was one of the first stegosaurians found. Its only remains, a partial skull, isolated teeth, and fragments of vertebrae, were found in the Kirkwood Formation. British paleontologist Richard Owen initially identified the fragments as those of the pareiasaur Anthodon. After remaining untouched for years in the British Museum of Natural History, the partial skull was identified by South African paleontologist Robert Broom as belonging to a different genus; he named the specimen Palaeoscincus africanus. Several years later, Hungarian paleontologist Franz Nopcsa, unaware of Broom's new name, similarly concluded that it represented a new taxon, and named it Paranthodon owenii. Since Nopcsa's species name was assigned after Broom's, and Broom did not assign a new genus, both names are now synonyms of the current binomial, Paranthodon africanus. The genus name combines the Ancient Greek para (near) with the genus name Anthodon, to represent the initial referral of the remains.
In identifying the remains as those of Palaeoscincus, Broom initially classified Paranthodon as an ankylosaurian, a statement backed by the research of Coombs in the 1970s. In 1929, Nopcsa identified the taxon as a stegosaurid, with which most modern studies agree. In 1981, the genus was reviewed with modern taxonomic techniques, and found to be a valid genus of stegosaurid. A 2018 review of Paranthodon could only identify one distinguishing feature, and while that study still referred it to Stegosauria based on similarity and multiple phylogenetic analyses, no diagnostic features of the group could be identified in Paranthodon.Stegosauridae
Stegosauridae is a clade of thyreophoran dinosaurs (armoured dinosaurs) within the suborder Stegosauria. The clade is defined as all species of dinosaurs more closely related to Stegosaurus than Huayangosaurus. The name ‘Stegosauridae’ is thus a stem-based name taken from the well-represented genus – Stegosaurus (meaning ‘roofed lizard’). Fossil evidence of stegosaurids, dating from the Middle Jurassic through the Early Cretaceous, have been recovered from North America, Eurasia and Africa. On the other hand, Stegosauridae's sister clade, huayangosaurids, can be traced only to the Middle Jurassic.The clade Stegosauridae is composed of the genera Stegosaurus, Dacentrurus, Miragaia, Loricatosaurus, and Kentrosaurus, with the last considered to be at the base of the clade. 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, where they give way to paired of spikes. 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.
Stegosaurids are distinguished from huayangosaurids in that the former have lost the plesiomorphic pre-maxillary teeth and lateral scute rows along the trunk. Furthermore, stegosaurids as opposed to huayangosaurids have long narrow skulls and longer hindlimbs compared to their forelimbs. However, these two features are not diagnostic of Stegosauridae because they may also be present in non-stegosaurids other than huayangosaurids.Tatisaurus
Tatisaurus is a genus of ornithischian dinosaur from the Early Jurassic from the Lower Lufeng Formation in Yunnan Province in China. Little is known as the remains are fragmentary.Thyreophora
Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the early Jurassic Period until the end of the Cretaceous.
Thyreophorans are characterized by the presence of body armor lined up in longitudinal rows along the body. Primitive forms had simple, low, keeled scutes or osteoderms, whereas more derived forms developed more elaborate structures including spikes and plates. Most thyreophorans were herbivorous and had relatively small brains for their body size.
Thyreophora includes various subgroups, including the suborders Ankylosauria and Stegosauria. In both the suborders, the forelimbs were much shorter than the hindlimbs, particularly in stegosaurs. The clade has been defined as the group consisting of all species more closely related to Ankylosaurus than to Triceratops. Thyreophora is the sister group of Cerapoda within Genasauria.Tuojiangosaurus
Tuojiangosaurus (meaning "Tuo River lizard") is a genus of herbivorous stegosaurid dinosaur from the Late Jurassic Period, recovered from the Upper Shaximiao Formation of what is now Sichuan Province in China.Wuerhosaurus
Wuerhosaurus is a genus of stegosaurid dinosaur from the Early Cretaceous Period of China and Mongolia. As such, it was one of the last genera of stegosaurians known to have existed, since most others lived in the late Jurassic.Yingshanosaurus
Yingshanosaurus (meaning "Yingshan or Golden Hills reptile") is a genus of stegosaurian dinosaur from the Late Jurassic, around 155 million years ago. It was a herbivore that lived in what is now China. The type species is Yingshanosaurus jichuanensis.