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.
|Mounted skeleton of Stegosaurus specimen Natural History Museum, London|
The cranial remains of stegosaurids, like all stegosaurians, are rarely discovered. Hence, a significant portion of the knowledge of their skull morphology comes from few complete skulls discovered of Stegosaurus and fragmentary remains of other stegosaurids. In general, stegosaurids have proportionally long, low and narrow snouts with a deep mandible, compared to that of Huayangosaurus. Stegosaurids also lack premaxillary teeth.
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. The genuine absence of parascapular spines in other stegosaurids is considered a secondary loss since many basal stegosaurs like Gigantspinosaurus and Huayangosaurus have been discovered with them.
Stegosaurids also lack lateral scute rows that run longitudinally on either side of the trunk in huayangosaurids and ankylosaurs, 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 other non-huayangosaurid stegosaurs, whose phylogenetic relations within Stegosauria are unclear.
Stegosaurids exhibit the characteristic dorsal osteoderms, found in all stegosaurs, in the form of erect plates and spines. Stegosaurid plates have a thick base and central portion, but are transversely thin elsewhere. The plates become remarkably large and thin in Stegosaurus. They are found in varying sizes along the dorsum, with the central region of the back usually having the largest and tallest plates. The arrangement of these parasagittal dorsal plates has been intensely debated in the past. Marsh suggested a single median row of plates running post-cranially along the longitudinal axis and Lull argued in favour of bilaterally paired arrangement throughout the series. Current scientific consensus lies in the arrangement proposed by Gilmore - two parasagittal rows of staggered alternates, after the discovery of an almost complete skeleton preserved in this manner in rock. Furthermore, no two plates share the same size and shape, making the possibility of bilaterally paired rows even less likely. Plates are usually found with distinct vascular grooves on their lateral surfaces, suggesting the presence of a circulatory network. Stegosaurids also have osteoderms on the throat in the form of small depressed ossicles and two pairs of elongated spike-like tail-spines.
In an ontogenetic histological analysis of Stegosaurus plates and spikes, Hayashi et al. (2012) examined their structure and function through juveniles to old adults. They found that throughout the ontogeny, the dorsal osteoderms are composed of dense ossified collagen fibres in both the cortical and cancellous sections of the bone, suggesting that plates and spikes are formed from the direct mineralization of already existing fibrous networks in the skin. However, the many structural features, seen in the spikes and plates of old adults specimens, are acquired at different stages of development. Extensive vascular networks form in the plates during the change from juveniles to young adults and persist in old adults but spikes acquire a thick cortex with a large axial vascular channel only in old adults. Hayashi et al. argue that the formation of nourishing vascular networks in young adults supported the growth of large plates. This would have enhanced the size of the animal, which may have helped attract mates and deter rivals. Furthermore, the presence of the vascular networks in the plates of the young adult indicate a secondary use of the plates as a thermoregulatory device for heat loss much like the elephant ear, toucan bill or alligator osteoderms. The thickening of the cortical section of the bone and the compaction of bone in the terminal tail-spikes in old adults suggest that they were used as defence weapons, but not until an ontogenetically late stage. The development of the large axial channel in old adults from small canals in young adults, facilitated the further enlargement of the spikes by increasing the amount of nourishment supplied. On the other hand, plates do not show a similar degree of bone compaction or cortical thickening indicating they would not be capable of taking much weight from above. This suggests they were not as important as spikes in active defense.
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.
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.
In 1877, Othniel Marsh discovered and named Stegosaurus armatus, from which the name of the family ‘Stegosauridae’ was erected in 1880. In comparison to Huayangosauridae, notable synapomorphies of Stegosauridae include a large antitrochanter (supracetabular process) in the ilium, a long prepubic process and long femur relative to the length of the humerus. Furthermore, stegosaurid sacral ribs are T-shaped in parasagittal cross-section and the dorsal vertebrae have an elongated neural arch.
Stegosaurid specimens originally described under the genera Wuerhosaurus and Hesperosaurus were referred to the genus Stegosaurus, under the names Stegosaurus homheni and Stegosaurus mjosi, respectively, by Maidment et al. (2010). Furthermore, many Stegosaurus specimens that were previously believed to from different species, within the genus, were all assigned to Stegosaurus armatus. This reclassification of the specimens occurred after finding that all differences between specimens could be explained by intraspecific variation.
The structure of the stegosaurid family tree has been debated for a while. However, in two of the most extensive cladistics analyses of Stegosauria conducted to date, both Mateus et al. (2009) and Maidment (2010) present similar phylogenetic relationships within Stegosauridae (shown below). The well-resolved phylogenies place the newly discovered long-necked stegosaurid Miragaia as sister taxa to Dacentrurus forming the clade Dacentrurinae. Mateus et al. note that in both Miragaia and Dacentrurus, the cervical rib projects posteriorly and the anterior pubic process is dorsoventrally deep and bears a dorsal projection at its anterior tip in lateral view. Their phylogeny also points to a sister-group relationship between the new clade Dacentrurinae and the genus Stegosaurus, supported by the shared presence of postzygapophyses on cervical vertebrae that are elongate and project posterior to the posterior centrum facet. Dacentrurus was previously considered to be a basal stegosaurid, but the discovery and observation of Miragaia has suggested that it is a derived taxon.
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-tailed against predators as a clubbing device.
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 (12mm 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.
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 sauropod dinosaurs, which also achieved the elongation of the neck through similar mechanisms and had access to fodder higher off the ground.
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.
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.
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.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.Dystrophaeus
Dystrophaeus is the name given to an extinct genus of eusauropod dinosaur from the early Kimmeridgian stage of the Late Jurassic that existed around 154.8 Ma. Its fossils were found in the Tidwell Member of the Morrison Formation of Utah. Its estimated mass is 12 tonnes (13 short tons).The type species, D. viaemalae, was described by Edward Drinker Cope in 1877. The genus name means "coarse joint" from Greek dys, "bad", and stropheus, "joint", a reference to the pitted joint surfaces serving as an attachment for cartilage. The specific name reads as Latin viae malae, "of the bad road", a reference to the various arduous routes taken to find, reach and salvage the remains. It consists of one partial skeleton, the holotype USNM 2364, which includes a 76 centimetre long ulna, a scapula, a partial radius, and some metacarpals discovered in August 1859 by John Strong Newberry. It was found in what is possibly stratigraphic zone 1 of the Morrison, although an older Oxfordian-Callovian has also been suggested. Dystrophaeus represents one of the oldest discoveries of sauropods in America; earlier, in 1855, some teeth had been found of Astrodon.
The classification of Dystrophaeus has been rather confusing. Cope in 1877 merely concluded it was some Triassic dinosaur. Henri-Émile Sauvage in 1882 understood it was a sauropod, assigning it to the Atlantosauridae. Othniel Charles Marsh however, in 1895 stated it belonged to the Stegosauridae. Friedrich von Huene, the first to determine it was of Jurassic age, in 1904 created a special family for it, the Dystrophaeidae, which he assumed to be herbivorous theropods. Only in 1908 von Huene realised his mistake and classified it in the sauropod Cetiosauridae, refining this in 1927 to the Cardiodontinae. Alfred Romer in 1966 put it in the Brachiosauridae, in a subfamily Cetiosaurinae.
More recently, an analysis by David Gillette concluded it was a member of the Diplodocidae. Another recent review, by Tschopp and colleagues in 2015, suggest it is a member of the Dicraeosauridae. However, many researchers consider the taxon to be a nomen dubium.Eoplophysis
Eoplophysis is a genus of stegosaur known from the Middle Jurassic Cornbrash Formation, Sharp's Hill Formation, and Chipping Norton Formation of England.Hesperosaurus
Hesperosaurus (meaning "western lizard", from Classical Greek ἕσπερος/hesperos "western" and σαυρος/sauros "lizard") is a herbivorous stegosaurian dinosaur from the Kimmeridgian epoch of the Jurassic period, approximately 156 million years ago.
Fossils of Hesperosaurus have since 1985 been found in the state of Wyoming and Montana in the United States of America. The type species Hesperosaurus mjosi was named in 2001. It is from an older part of the Morrison Formation, and so a little older than other Morrison stegosaurs. Several relatively complete skeletons of Hesperosaurus are known. One specimen preserves the first known impression of the horn sheath of a stegosaurian back plate.
Hesperosaurus was six to seven metres long and two to three tonnes in weight. It was a member of the Stegosauridae, quadrupedal plant-eaters protected by vertical bony plates and spikes. It was closely related to Stegosaurus and was similar to it in having two rows of, possibly alternating, plates on its back and four spikes on its tail end. The plates on its back were perhaps not as tall, but were longer. It possibly had a deeper skull than Stegosaurus.Jiangjunosaurus
Jiangjunosaurus is a genus of herbivorous stegosaurian dinosaur from the Oxfordian-age (Upper Jurassic) Shishugou Formation of the Junggar Basin, Xinjiang, China.Kentrosaurus
Kentrosaurus ( KEN-tro-SAWR-əs) is a genus of stegosaurian dinosaur from the Late Jurassic of Tanzania. The type species is K. aethiopicus, named and described by German palaeontologist Edwin Hennig in 1915. Often thought to be a "primitive" member of the Stegosauria, several recent cladistic analyses find it as more derived than many other stegosaurs, and a close relative of Stegosaurus from the North American Morrison Formation within the Stegosauridae.
Fossils of K. aethiopicus have been found only in the Tendaguru Formation, dated to the late Kimmeridgian and early Tithonian ages, about 152 million years ago. Hundreds of bones were unearthed by German expeditions to German East Africa between 1909 and 1912. Although no complete skeletons are known, the remains provided a nearly complete picture of the build of the animal.
Kentrosaurus generally measured around 4.5 metres (15 ft) in length as an adult, and weighed about one tonne (1.1 tons). It walked on all fours with straight hindlimbs. It had a small, elongated head with a beak used to bite off plant material that would be digested in a large gut. It had a, probably double, row of small plates running down its neck and back. These plates gradually merged into spikes on the hip and tail. The longest spikes were on the tail end and were used to actively defend the animal. There also was a long spike on each shoulder. The thigh bones come in two different types, suggesting that one sex was larger and more stout than the other.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.Miragaia longicollum
Miragaia (named after Miragaia, the parish in France and geologic unit where its remains were found) is a side-necked
stegosaurid dinosaur. Its fossils have been found in Lower Jurassic rocks in France. Miragaia has the sidest neck known for any stegosaurian, which included at least seventeen vertebrae.Mongolostegus
Mongolostegus is a genus of stegosaur from the Early Cretaceous (Aptian-Albian) of Mongolia. The type and only species is M. exspectabilis, known from a single specimen previously under the nomen nudum Wuerhosaurus mongoliensis.Monkonosaurus
Monkonosaurus (meaning "Monkon lizard") is a dubious genus of herbivorous stegosaurian dinosaur from the Late Jurassic (Kimmeridgian stage, around 150-155 million years ago) of Tibet (and the cretaceous Lura Formation in China). Other sources place it to Oxfordian - Albian stages (163 - 100 mya).
The genus was formalized by Zhao Xijin in 1986. The generic name refers to Markam County, also known as Monko. Zhao at the time gave neither a description, meaning the name remained a nomen nudum, nor a specific name. The latter was provided in 1986 when the type species Monkonosaurus lawulacus was named, the epithet referring to the Lawushan, the Lawu mountains. The first description was provided in 1990 by Dong Zhiming.The holotype, IVPP V 6975, was found in a layer of the Lura Formation dating from the latest Jurassic. It consists of partial skeleton lacking the skull. It contains a pelvis with sacrum, two vertebrae and three back plates. The fragmentary condition of this single skeleton places doubt on the validity of this genus, some studies concluding it is a nomen dubium.Monkonosaurus was about five metres long. The ilium has a length of 905 millimetres. The sacrum consists of five sacral vertebrae.Zhao placed Monkonosaurus in the Oligosacralosauroidea. Later researchers considered it an indeterminate member of the Stegosauridae.Nodosaurinae
Nodosaurinae is a group of ankylosaurian dinosaurs named in 1919 by Othenio Abel.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.Regnosaurus
Regnosaurus (meaning "Sussex lizard") is a genus of herbivorous stegosaurian dinosaur that lived during the Early Cretaceous Period in what is now England.Stegosauria
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.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.