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Stegosauria is a group of herbivorous ornithischian
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s that lived during the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
and early
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
periods. Stegosaurian fossils have been found mostly in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
, predominantly in what is now
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,
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,
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
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and
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. 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 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. 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 Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
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.


Description


Skull

Stegosaurians had characteristic small, long, flat, narrow heads and a horn-covered beak or
rhamphotheca The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...
, which covered the front of the snout (two premaxillaries) and lower jaw (a single predentary) bones. Similar structures are seen in
turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...
s and
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s. Apart from ''
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 ...
'', 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.


Postcranial skeleton

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 A condyle (;Entry "condyle"
in
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 The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists ...
was very robust. In ''Huayangosaurus'', the
acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The ...
, a process on the lower front edge of the
shoulderblade The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either ...
, was moderately developed; the coracoid was about as wide as the lower end of the
scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...
, 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 bone The ilium () (plural ilia) is the uppermost and largest part of the hip bone, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bon ...
s 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 Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures approximately east to ...
and pubic bones. In more derived species, these became more horizontal and shorter to the rear, while the front prepubic process lengthened.


Osteoderms

Like all Thyreophora, stegosaurians were protected by bony scutes that were not part of the skeleton proper but skin ossifications instead: the so-called
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...
s. ''Huayangosaurus'' had several types. On its neck, back, and tail were two rows of paired small vertical plates and spikes. 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 ''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. Description According to Dong e.a. the ''Chungkingo ...
'' 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 Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...
.


Discovery

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 ''Regnosaurus'' (meaning "Sussex lizard") is a genus of herbivorous stegosaurian dinosaur that lived during the Early Cretaceous Period in what is now England. It was one of the first stegosaurs disvovered. Discovery and species The fossil r ...
''. In 1845, in the area of the present state of
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, remains were discovered that much later would be named '' Paranthodon''. In 1874, other remains from England were named '' Craterosaurus''. 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 of what was clearly a large herbivore equipped with spikes were uncovered in England; the first partial stegosaurian skeleton known. They were named ''Omosaurus'' by
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...
in 1875. Later, this name was shown to be preoccupied by the phytosaur ''
Omosaurus ''Omosaurus'' is a dubious genus of extinct crurotarsan reptile, possibly a phytosaur, from the Late Triassic (Carnian) of North Carolina. Only scant remains are known, which makes ''Omosaurus'' hard to classify. The type, and only specie ...
'' 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''. In 1877, Arthur Lakes, a fossil hunter working for Professor
Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
, in
Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...
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.Maidment, S.C.R., 2010, "Stegosauria: A review of the body fossil record and phylogenetic relationships", ''Swiss Journal of Geosciences'', 103: 199-210 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 ''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. Description According to Dong e.a. the ''Chungkingo ...
'', ''
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 ...
'', '' 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 Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of th ...
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 Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
, allowing for the first time to exactly calculate stegosaurian evolutionary relationships.


Classification

The Stegosauria was originally named as an order within Reptilia by
O.C. Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...
in 1877.Marsh, O.C. (1877). "New order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains." ''American Journal of Science'', 14(ser.3):513-514. 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 Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at si ...
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,
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and possibly
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. The first exact clade definition of Stegosauria was given by
Peter Malcolm Galton Peter Malcolm Galton (born 14 March 1942 in London) is a British vertebrate paleontologist who has to date written or co-written about 190 papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosaur ...
in 1997: all thyreophoran Ornithischia more closely related to ''Stegosaurus'' than to ''
Ankylosaurus ''Ankylosaurus'' is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of th ...
''. Thus defined, the Stegosauria are by definition the sister group of the Ankylosauria within the Eurypoda.


Phylogeny

Kenneth Carpenter of the Denver Museum of Nature and Science published a preliminary phyletic treeCarpenter, K., Miles, C.A., and Cloward, K. (2001). "New Primitive Stegosaur from the Morrison Formation, Wyoming", in Carpenter, Kenneth(ed) ''The Armored Dinosaurs''. Indiana University Press. , 55–75. 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:


Undescribed species

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.


Evolutionary history

Like the spikes and shields of
ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
s, the bony plates and spines of stegosaurians evolved from the low-keeled osteoderms characteristic of basal thyreophorans.Norman, David (2001). "''Scelidosaurus'', the earliest complete dinosaur" in ''The Armored Dinosaurs'', pp 3-24. Bloomington: Indiana University Press. . 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 Sir Francis Galton, FRS FRAI (; 16 February 1822 – 17 January 1911), was an English Victorian era polymath: a statistician, sociologist, psychologist, anthropologist, tropical explorer, geographer, inventor, meteorologist, prot ...
(2019) interpreted plates of an armored dinosaur from the Lower Jurassic ( Sinemurian- Pliensbachian) Lower Kota Formation of
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
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 England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...
represent the oldest probable record of stegosaurians reported so far. Outside that, there are assigned fossils to stegosauria from the
Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toar ...
: the specimen "IVPP V.219", a chimaera with bones of the sauropod '' Sanpasaurus'' is known from the Maanshan Member of the
Ziliujing Formation The Ziliujing Formation is a geological formation in China, It is Early Jurassic in age. It is part of the stratigraphy of the Sichuan Basin. The dinosaur ''Gongxianosaurus'' and indeterminate theropod material are known from the Dongyuemiao Mem ...
. 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 (stage), 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 ''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. Description According to Dong e.a. the ''Chungkingo ...
'', '' 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 Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. 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 South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
. The only more substantial discoveries are those of '' Wuerhosaurus'' from Northern China, the exact age of which is highly uncertain 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 which dates 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. 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 Sir Francis Galton, FRS FRAI (; 16 February 1822 – 17 January 1911), was an English Victorian era polymath: a statistician, sociologist, psychologist, anthropologist, tropical explorer, geographer, inventor, meteorologist, prot ...
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''. 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).


Paleobiology


Trace fossils

Stegosaurian tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Cleveland-Lloyd Dinosaur Quarry, 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 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 Formation, 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. '' 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 scally skin pattern. Australia's 'Dinosaur Coast' in Broome, Western Australia, 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. While has no body fossil evidence currently known for stegosaurs, handprints from underground coal mines near Oakey, Queensland, 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.


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 T. Bakker, Robert Bakker noted that it is likely that the stegosaur tail was much more flexible than those of other ornithischian 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, Kentrosaurus aethiopicus'' showed that the tail could bring the thagomizer around to the sides of the dinosaur, possibly striking an attacker beside it. In 2001, a study of tail spikes by McWhinney et al., 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.


References


External links


Stegosauria on Palaeos.com
* https://web.archive.org/web/20080727011652/http://www.kheper.net/evolution/dinosauria/Stegosauria.htm {{Taxonbar, from=Q131484 Stegosaurs, Bajocian first appearances Early Cretaceous extinctions Fossil taxa described in 1877 Taxa named by Othniel Charles Marsh