''Ouranosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of herbivorous basal hadrosauriform

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 ...

that lived during the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

stage of the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

of modern-day

Niger ) , official_languages = , languages_type = National languagesCameroon Cameroon (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west-central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; the C ...

. ''Ouranosaurus'' measured about long. Two rather complete fossils were found in the

Elrhaz Formation The Elrhaz Formation is a geological formation in Niger, central Africa. Its strata date back to the Early Cretaceous, about 125 to 112 million years ago. Dinosaur remains are among the fossils that have been recovered from the formation, alongsi ...

Gadoufaoua The Elrhaz Formation is a geological formation in Niger, central Africa. Its strata date back to the Early Cretaceous, about 125 to 112 million years ago. Dinosaur remains are among the fossils that have been recovered from the formation, alongsi ...

deposits,

Agadez Agadez ( Air Tamajeq: ⴰⴶⴰⴷⴰⵣ, ''Agadaz''), formerly spelled Agadès, is the fifth largest city in Niger, with a population of 110,497 based on the 2012 census. The capital of Agadez Region, it lies in the Sahara desert, and is also ...

, Niger, in 1965 and 1970, with a third indeterminate specimen known from the Koum Formation of Cameroon. The animal was named in 1976 by French paleontologist

Philippe Taquet Philippe Taquet (b. April 25, 1940 Saint-Quentin, Aisne) is a French paleontologist who specializes in dinosaur systematics of finds primarily in northern Africa. He is a member of the French Academy of Sciences since November 30, 2004, president ...

; the type species being ''Ouranosaurus nigeriensis''. The generic name is a combination of ''ourane,'' a word with multiple meanings ("an Arabic name that signifies valor, courage, recklessness"; the

Tuareg The Tuareg people (; also spelled Twareg or Touareg; endonym: ''Imuhaɣ/Imušaɣ/Imašeɣăn/Imajeɣăn'') are a large Berber ethnic group that principally inhabit the Sahara in a vast area stretching from far southwestern Libya to southern A ...

name of the

desert monitor The desert monitor (''Varanus griseus'') is a species of monitor lizard of the order Squamata found living throughout North Africa and Central and South Asia. The desert monitor is carnivorous, feeding on a wide range of vertebrates and invert ...

given by the

Berbers , image = File:Berber_flag.svg , caption = The Berber ethnic flag , population = 36 million , region1 = Morocco , pop1 = 14 million to 18 million , region2 = Algeria , pop2 ...

of Niger & Algeria), and ''sauros'', the Greek word for lizard. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''nigeriensis'' alludes to ''

Niger ) , official_languages = , languages_type = National languages

Discovery and naming

Five French palaeontological expeditions were undertaken in the

region of the

Sahara Desert , photo = Sahara real color.jpg , photo_caption = The Sahara taken by Apollo 17 astronauts, 1972 , map = , map_image = , location = , country = , country1 = , ...

Niger ) , official_languages = , languages_type = National languages1965 Events January–February * January 14 – The Prime Minister of Northern Ireland and the Taoiseach of the Republic of Ireland meet for the first time in 43 years. * January 20 ** Lyndon B. Johnson is Second inauguration of Lyndo ...

and

1972 Within the context of Coordinated Universal Time (UTC) it was the longest year ever, as two leap seconds were added during this 366-day year, an event which has not since been repeated. (If its start and end are defined using Solar time, me ...

and led by French

palaeontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

. These deposits come from GAD 5, a layer in the upper

of the Tégama Group, which was deposited during the

stage of the

. On the first expedition, lasting from January–February 1965, eight

iguanodontia Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', '' Tenontosaurus'', and the hadrosaurids or "duck-bil ...

n specimens were discovered at the "niveau des Innocents" site, east of the Emechedoui wells. An additional two skeletons were discovered southeast of Elrhaz in the "Camp des deux Arbres" locality, which were given the field numbers GDF 300 and GDI 381. Both were collected in the February–April 1996 expedition, the former including a nearly complete but scattered skeleton, and the latter a skeleton that was two-thirds preserved. The skeletons then in 1967 were brought to the

Muséum National d'Histoire Naturelle The French National Museum of Natural History, known in French as the ' (abbreviation MNHN), is the national natural history museum of France and a ' of higher education part of Sorbonne Universities. The main museum, with four galleries, is loc ...

of Paris, where they were prepared. GDF 381 was recategorized with the number MNHN GDF 1700 and then later described in 1999 as the holotype of the new taxon ''

Lurdusaurus arenatus ''Lurdusaurus'' ("heavy lizard") is a genus of massive and unusually shaped iguanodont dinosaur from the Elrhaz Formation in Niger. It contains one species, ''L. arenatus''. The formation dates to the Early Cretaceous, roughly 112 million years ...

''. While the third expedition did not turn up additional iguanodontian material, the fourth in January–March

1970 Events January * January 1 – Unix time epoch reached at 00:00:00 UTC. * January 5 – The 7.1 Tonghai earthquake shakes Tonghai County, Yunnan province, China, with a maximum Mercalli intensity scale, Mercalli intensity of X (''Extrem ...

uncovered a nearly complete and partially articulated skeleton lacking the skull, south of the "niveau des Innocents" site, and was also given the field number GDF 381. This specimen was collected and taken to the MNHN by the fifth expedition in

. Following a subsequent Italian-French expedition led by Taquet and Italian palaeontologist

Giancarlo Ligabue Giancarlo Ligabue (30 October 1931 – 25 January 2015) was an Italian paleontologist, scholar, politician and businessman. Born in Venice, Ligabue graduated in Economics at the Ca' Foscari University of Venice and in Geology at la Sorbonne, and ...

that turned up a potential additional iguanodontian specimen, Ligabue offered to donate the nearly complete specimen and a skull of ''

Sarcosuchus ''Sarcosuchus'' (; ) is an extinct genus of crocodyliform and distant relative of living crocodilians that lived during the Early Cretaceous, from the late Hauterivian to the early Albian, 133 to 112 million years ago of what is now Africa and ...

'' to the Municipality of Venice, which accepted the offer and subsequently mounted the skeleton in

1975 It was also declared the ''International Women's Year'' by the United Nations and the European Architectural Heritage Year by the Council of Europe. Events January * January 1 - Watergate scandal (United States): John N. Mitchell, H. R. ...

at the

Museo di Storia Naturale di Venezia Museo di Storia Naturale di Venezia ( en, Natural History Museum of Venice) is a museum of natural history housed in Fondaco dei Turchi, located on the Grand Canal, Venice, Italy. Its collections relate mainly to the natural history of the Ve ...

. Taquet formally described the two mostly-complete specimens MNHN GDF 300 and MNHN GDF 381 from the first and fourth expeditions as ''Ouranosaurus nigeriensis'' in

1976 Events January * January 3 – The International Covenant on Economic, Social and Cultural Rights enters into force. * January 5 – The Pol Pot regime proclaims a new constitution for Democratic Kampuchea. * January 11 – The 1976 Phila ...

, along with a referred

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

and

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

that bore the numbers MNHN GDF 301 and MNHN GDF 302 respectively. MNHN GDF 300 was made the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, and was the primary specimen described, including a semi-articulated skull lacking the left , right and the , almost the entire

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

, forelimbs lacking a few hand bones, and most of the right hindlimb and a few bones of the left. Additional description for bones unpreserved in the holotype was based on Taquet's MNHN GDF 381, which was not mentioned as having been sent to Venice and renumbered as MSNVE 3714, although this was confirmed by Italian palaeontologist Filippo Bertozzo and colleagues in 2017. The holotype itself was returned to Niger after being described and having its bones cast and mounted, and is now on display at the Musée National Boubou Hama in

Niamey Niamey () is the capital and largest city of Niger. Niamey lies on the Niger River, primarily situated on the east bank. Niamey's population was counted as 1,026,848 as of the 2012 census. As of 2017, population projections show the capital di ...

. The generic name ''Ouranosaurus'' carries a double meaning, it is both taken from

Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C ...

meaning "valour", "bravery " or "recklessness" and also from the local

Tuareg language The Tuareg () languages constitute a group of closely related Berber languages and dialects. They are spoken by the Tuareg Berbers in large parts of Mali, Niger, Algeria, Libya and Burkina Faso, with a few speakers, the ''Kinnin'', in Chad. Desc ...

of Niger where it is the name they call the

. The specific name refers to Niger, the country of discovery. Taquet had used the name "Ouranosaurus nigeriensis" previously, first in a public presentation of the skeleton MNHN GDF 300 in July 1972, then later in September 1972 in a news article and again in December 1972 in a book; only the book bore any images associated with the name, and none of the earlier mentions had a diagnosis to make the name valid.

Description

''Ouranosaurus'' was a relatively large iguanodontian, estimated by Taquet in 1976 to have a body length of and a weight of . A lighter weight of was suggested by American palaeontologist

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

in 2010 due to the leaner build observed in the animal compared to relation, although a longer length of was given. The holotype and paratype specimens were suggested to belong to subadults by Bertozzo ''et al.'' in 2017, although they would have been close to adult size. MSNVE 3714 is long as mounted, although a few caudals are missing, and is roughly 90% the length of the holotype, which would be long. The variation between the sizes fits within the range of variation between adult individuals of ''

Iguanodon ''Iguanodon'' ( ; meaning ' iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, ...

'', so there is a chance that the larger holotype and smaller paratype were same ontogenetic stage.

Skull

The skull of ''Ouranosaurus'' is long. It was rather low, being wide and only tall. The top of the skull was flat, the highest point being just in front of the

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

and sloping down towards both the rear of the skull and the tip of the snout. This makes ''Ouranosaurus'' have the most elongate skull of any non-

hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...

, the length being 3.8 times the maximum height, although the skull is proportionally wider than related ''

Mantellisaurus ''Mantellisaurus'' is a genus of iguanodontian dinosaur that lived in the Barremian and early Aptian ages of the Early Cretaceous Period of Europe. Its remains are known from Belgium ( Bernissart), England, Spain and Germany. The type and only ...

''. Bones of the snout are more loosely articulated with each other than the bones of the posterior skull. The are long, with very deep as in other iguanodontians. Anteriorly, the premaxillae flare gently laterally into a rugose surface for a beak, like other iguanodontians, although dissimilar from ''

'' and similar to hadrosaurids the nares are entirely visible from above. Neither premaxilla bears any teeth, although the very anterior tip has "pseudo-teeth" formed by multiple denticles on the margin of the bone. Only the right maxilla of ''Ouranosaurus'' is known. although it is well preserved forming a triangle long and tall, much taller proportionally than ''Iguanodon''. The maxilla bears faces for articulation with the premaxilla in front, above, , , and possibly internally, and to the rear. The lacrimal process is the highest point of the maxilla, and behind this process is a smooth and curved margin for the , which is bounded by the maxilla in front and below, lacrimal above, and jugal behind. The jugal overlaps only the posterior end of the maxilla, which is unlike hadrosaurids where there is more overlap. The dental edge of the maxilla is slightly arced, and above the toothrow is a shallow depression bearing , also known as the buccal emargination that is diagnostic of

Ornithischia Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...

. 20 teeth are preserved in the maxilla, although the anterior end of the toothrow is broken and Taquet (1976) predicted the total number to be 22. Ouranosaurus head

Many of the central bones of the skull are the same form as those of hadrosaurids or related iguanodontians like ''Iguanodon'' and ''Mantellisaurus''. The jugal below and behind the orbit bears the same shape as in hadrosaurids, with a high rear process, and articulated with the quadratojugal and quadrate that are also very similar to more derived taxa. As in other

ornithopods Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...

, the is a tri-radiate bone surrounding sides of the orbit, and . Contact between the postorbital and the excludes the flattened and wide from the supratemporal fenestra. In ''Ouranosaurus'' and related taxa the are small, and articulates with the broadened and textured lacrimal. Only a single was present in ''Ouranosaurus'', which projects into the orbit above the eye. The of ''Ouranosaurus'' are unique among ornithischians. The bones are unfused suggesting mobility, and at their ends on the top of the skull are rounded domes, which were described by Taquet (1976) as distinct and rugose "nasal protuberances". The snout was toothless and covered in a horny sheath during life, forming a very wide beak together with a comparable sheath on the short

predentary Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

bone at the extreme front of the lower jaws. However, after a rather large

diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...

with the beak, there were large batteries of cheek teeth on the sides of the jaws: the gaps between the teeth crowns were filled by the points of a second generation of replacement teeth, the whole forming a continuous surface. Contrary to the situation with some related species, a third generation of erupted teeth was lacking. There were twenty-two tooth positions in both lower and upper jaw, for a total of eighty-eight.

Postcranial skeleton

The most conspicuous feature of ''Ouranosaurus'' is a large "sail" on its back, supported by long, wide,

neural spine The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

s, that spanned its entire rump and tail, resembling that of ''

Spinosaurus ''Spinosaurus'' (; ) is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago. The genus was known first f ...

'', a well-known meat-eating dinosaur also known from northern Africa. These tall neural spines did not closely resemble those of sail-backs such as '' Dimetrodon'' of the

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

Period. The supporting spines in a sailback become thinner distally, whereas in ''Ouranosaurus'' the spines actually become thicker distally and flatten. The posterior spines were also bound together by ossified tendons, which stiffened the back. Finally, the spine length peaks over the forelimbs. The first four dorsal vertebrae are unknown; the fifth already bears a that is pointed and slightly hooked; Taquet presumed it might have anchored a tendon to support the neck or skull. The tenth, eleventh and twelfth spines are the longest, at about . The last dorsal spine, the seventeenth, has a grooved posterior edge, in which the anterior corner of the lower spine of the first

sacral vertebra The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

is locked. The spines over the six sacral vertebrae are markedly lower, but those of the tail base again longer; towards the end of the tail the spines gradually shorten. Ouranosaurus - dorsal vertebrae

The dorsal "sail" is usually explained as either functioning as a system for

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 temperature ...

or a display structure. An alternative hypothesis is that the back might have carried a hump consisting of muscle tissue or fat, resembling that of a

bison Bison are large bovines in the genus ''Bison'' (Greek: "wild ox" (bison)) within the tribe Bovini. Two extant and numerous extinct species are recognised. Of the two surviving species, the American bison, ''B. bison'', found only in North Ame ...

camel A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. C ...

, rather than a sail. It could have been used for energy storage to survive a lean season. The axial column consisted of eleven neck vertebrae, seventeen dorsal vertebrae, six sacral vertebrae and forty tail vertebrae. The tail was relatively short. The front limbs were rather long with 55% of the length of the hind limbs. A quadrupedal stance would have been possible. The

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

was very straight. The hand was lightly built, short and broad. On each hand ''Ouranosaurus'' bore a

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

or spike that was much smaller than that of the earlier ''Iguanodon''. The second and third digits were broad and

hoof The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rum ...

-like, and anatomically were good for walking. To support the walking hypothesis, the

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...

was large and its component bones fused together to prevent its

dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sl ...

. The last digit (number 5) was long. In related species the fifth finger is presumed to have been prehensile: used for picking food like leaves and twigs or to help lower the food by lowering branch to a manageable height. Taquet assumed that with ''Ouranosaurus'' this function had been lost because the fifth

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...

, reduced to a spur, could no longer be directed sideways. Ouranosaurus nigeriensis restoration

The hindlimbs were large and robust to accommodate the weight of the body and strong enough to allow a bipedal walk. The

was slightly longer than the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

. This may indicate that the legs were used as pillars, and not for

sprinting Sprinting is running over a short distance at the top-most speed of the body in a limited period of time. It is used in many sports that incorporate running, typically as a way of quickly reaching a target or goal, or avoiding or catching an op ...

. Taquet concluded that ''Ouranosaurus'' was not a good runner because the fourth trochanter, the attachment point for the large retractor muscles connected to the tail base, was weakly developed. The foot was narrow with only three toes and relatively long. In the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

, the prepubis was very large, rounded and directed obliquely upwards.

Classification

Taquet originally assigned ''Ouranosaurus'' to the

Iguanodontidae Iguanodontidae is a family of iguanodontians belonging to Styracosterna, a derived clade within Ankylopollexia. Characterized by their elongated maxillae, they were herbivorous and typically large in size. This family exhibited locomotive dynam ...

, within the larger

Iguanodontia Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', '' Tenontosaurus'', and the hadrosaurids or "duck-bil ...

. However, although it shares some similarities with ''Iguanodon'' (such as a thumb spike), ''Ouranosaurus'' is no longer usually placed in the iguanodontid family, a grouping that is now generally considered

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

, a series of subsequent offshoots from the main stem-line of iguandontian evolution. It is instead placed in the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Hadrosauriformes Ankylopollexia is an extinct clade of ornithischian dinosaurs that lived from the Late Jurassic to the Late Cretaceous. It is a derived clade of iguanodontian ornithopods and contains the subgroup Styracosterna. The name stems from the Greek wor ...

, closely related to the

Hadrosauroidea Hadrosauroidea is a clade or superfamily of ornithischian dinosaurs that includes the "duck-billed" dinosaurs, or hadrosaurids, and all dinosaurs more closely related to them than to ''Iguanodon''. Their remains have been recovered in Asia, Europ ...

, which contains the Hadrosauridae (also known as "duck-billed dinosaurs") and their closest relatives. ''Ouranosaurus'' appears to represent an early specialized branch in this group, showing in some traits independent convergence with the hadrosaurids. It is thus a basal hadrosauriform. The simplified

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

below follows an analysis by Andrew McDonald and colleagues, published in November 2010 with information from McDonald, 2011. Venezia - Museo di storia naturale - Ouranosaurus nigeriensis

Venezia - Museo di storia naturale - Ouranosaurus nigeriensis

Paleobiology

Diet

The jaws were apparently operated by relatively weak muscles. ''Ouranosaurus'' had only small temporal openings behind the eyes, from which the larger capiti-mandibularis muscle was attached to the coronoid process on the lower jaw bone. Small rounded horns in front of its eyes made ''Ouranosaurus'' the only known horned

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous wo ...

. The back of the skull was rather narrow and could not compensate for the lack of a greater area of attachment for the jaw muscle, that the openings normally would provide, allowing for more power and a stronger bite. A lesser muscle, the musculus depressor mandibulae, used to open the lower jaws, was located at the back of the skull and was connected to a strongly projecting, broad and anteriorly oblique processus paroccipitalis. ''Ouranosaurus'' probably used its teeth to chew up tough plant food. A diet has been suggested of leaves, fruit, and seeds as the chewing would allow to free more energy from high quality food; the wide beak on the other hand indicates a specialisation in eating large amounts of low quality fodder. ''Ouranosaurus'' lived in a

river delta A river delta is a landform shaped like a triangle, created by deposition (geology), deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, res ...

Histology

''Ouranosaurus'' bears more similarities to other derived iguanodonts than more basal ornithopods. Remodeling is present in the subadult paratype, and high vascular density and circumferential arrangement of the microstructure suggests fast growth. Faster growth occurs in the same phylogenetic groups as higher body size, although their relationship is unclear. ''Ouranosaurus'' is a similar size to more basal ''

Tenontosaurus ''Tenontosaurus'' ( ; ) is a genus of medium- to large-sized ornithopod dinosaur. It was a relatively medium sized ornithopod, reaching in length and in body mass. It had an unusually long, broad tail, which like its back was stiffened with a n ...

'' which has slow growth, so either faster growth is caused by body size or ''Tenontosaurus'' is the maximum size of an ornithopod with a slow growth rate.

Paleoecology

''Ouranosaurus'' is known from the Elrhaz Formation of the Tegama Group in an area called Gadoufaoua, located in Niger. Only two mostly complete skeletons and up to 3 additional individuals have been found. The Elrhaz Formation consists mainly of

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

sandstones with low relief, much of which is obscured by sand dunes. The

sediments Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...

are coarse- to medium-grained, with almost no fine-grained horizons. ''Ouranosaurus'' is from the upper portion of the formation, probably Aptian in age. It likely lived in habitats dominated by inland

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

s (a

riparian zone A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...

). After the

iguanodontian Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include ''Camptosaurus'', ''Dryosaurus'', ''Iguanodon'', ''Tenontosaurus'', and the hadrosaurids or "duck-b ...

Lurdusaurus ''Lurdusaurus'' ("heavy lizard") is a genus of massive and unusually shaped iguanodont dinosaur from the Elrhaz Formation in Niger. It contains one species, ''L. arenatus''. The formation dates to the Early Cretaceous, roughly 112 million years ...

'', ''

Nigersaurus ''Nigersaurus'' is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in Niger. Fossils of th ...

'' was the most numerous

megaherbivore Megaherbivores (Greek μέγας megas "large" and Latin ''herbivora'' "herbivore") are large terrestrial herbivores that can exceed in weight. This polyphyletic group of megafauna includes elephants, rhinos, hippos, and giraffes. The largest ...

. Other herbivores from the same formation include ''Ouranosaurus'', ''

Elrhazosaurus ''Elrhazosaurus'' (meaning " Elrhaz lizard") is a genus of basal iguanodontian dinosaur, known from isolated bones found in Early Cretaceous rocks of Niger. These bones were initially thought to belong to a species of the related dryosaurid ' ...

'', and an unnamed

titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...

. It also lived alongside the

theropods Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...

Kryptops ''Kryptops'' is a genus of abelisaurid theropod dinosaur from the Early Cretaceous of Niger. It is known from a partial skeleton found at the Gadoufaoua locality in the western Ténéré Desert, in rocks of the Aptian-Albian age Elrhaz Formation ...

'', '' Suchomimus'', ''

Eocarcharia ''Eocarcharia'' (meaning "dawn shark") is a genus of carcharodontosaurid theropod dinosaur from the Early Cretaceous Elrhaz Formation that lived in the Sahara 112 million years ago, in what today is the country of Niger. It was discovered in 2 ...

'', ''

Carcharodontosaurus ''Carcharodontosaurus'' (; ) is a genus of large carcharodontosaurid theropod dinosaur that existed during the Cenomanian age of the Late Cretaceous in Northern Africa. The genus ''Carcharodontosaurus'' is named after the shark genus '' Carc ...

'', and ''

Afromimus ''Afromimus'' (meaning "Africa mimic") is a genus of theropod dinosaur from the Early Cretaceous Elrhaz Formation of Niger. It contains a single species, ''A. tenerensis'', named in 2017 by Paul Sereno from parts of the right leg, vertebrae, and ...

''.

Crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...

like ''

'', ''

Anatosuchus ''Anatosuchus'' ("duck crocodile", the name from the Latin ''anas'' ("duck") and the Greek ''souchos'' ("crocodile"), for the broad, duck-like snout) is an extinct genus of notosuchian crocodylomorph discovered in Gadoufaoua, Niger, and described ...

'', ''

Araripesuchus ''Araripesuchus'' is a genus of extinct crocodyliform that existed during the Cretaceous period of the late Mesozoic era some 125 to 66 million years ago. Six species of ''Araripesuchus'' are currently known. They are generally considered to be n ...

'', and ''

Stolokrosuchus ''Stolokrosuchus'' is an extinct genus of neosuchian crocodylomorph that lived during the Early Cretaceous. Its fossils, including a skull with a long thin snout and bony knobs on the prefrontal, have been found in Niger. ''Stolokrosuchus'' wa ...

'' also lived there. In addition, remains of a

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...

, chelonians, fish, a

hybodont Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like chondrichthyans, which existed from the late Devonian to the Late Cretaceous. They form the group of Elasmobranchii closest to neoselachians, the clade of modern shar ...

shark, and freshwater bivalves have been found. Grass did not evolve until the late Cretaceous.

References

Bibliography

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External links

''Ouranosaurus'' on Nature

(with picture) {{Taxonbar, from=Q131124 Iguanodonts Early Cretaceous dinosaurs of Africa Albian life Aptian life Cretaceous Niger Fossils of Niger Fossil taxa described in 1976 Taxa named by Philippe Taquet Ornithischian genera