''Nigersaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

rebbachisaurid Rebbachisauridae is a family of sauropod dinosaurs known from fragmentary fossil remains from the Cretaceous of South America, Africa, North America, Europe and possibly Central Asia. Taxonomy In 1990 sauropod specialist Jack McIntosh includ ...

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', ' lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their ...

dinosaur that lived during the middle

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 ...

period, about 115 to 105 million years ago. It was discovered 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 ...

in an area called Gadoufaoua, in

Niger ) , official_languages = , languages_type = National languagesPhilippe Taquet, who discovered the first remains. Small for a sauropod, ''Nigersaurus'' was about long, and had a short neck. It weighed around , comparable to a modern

elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...

. Its skull was very specialised for feeding, with large

fenestrae A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...

and thin bones. It had a wide muzzle filled with more than 500 teeth, which were replaced at a rapid rate: around every 14 days. The jaws may have borne a keratinous sheath. Unlike other

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s, the tooth-bearing bones of its jaws were rotated transversely relative to the rest of the skull, so that all of its teeth were located far to the front. Its skeleton was highly pneumatised (filled with air spaces connected to

air sacs Air sacs are spaces within an organism where there is the constant presence of air. Among modern animals, birds possess the most air sacs (9–11), with their extinct dinosaurian relatives showing a great increase in the pneumatization (presence o ...

), but the limbs were robustly built. ''Nigersaurus'' and its closest relatives are grouped within the subfamily

Rebbachisaurinae Rebbachisaurinae is a subfamily within the family Rebbachisauridae, defined to include '' Rebbachisaurus garasbae'' and exclude ''Limaysaurus tessonei''. It was first proposed as a rank by Jose Bonaparte in 1995, to include ''Rebbachisaurus''. S ...

(formerly thought to be grouped in the

eponymous An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...

Nigersaurinae) of the family Rebbachisauridae, which is part of the sauropod superfamily

Diplodocoidea Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like ''Supersaurus'', ''Diplodocus'', ''Apatosaurus'', and ''Amphicoelias''. Most had very long necks and long, ...

. ''Nigersaurus'' was probably a browser, and fed with its head close to the ground. The region of its brain that detected smell was underdeveloped, although its brain size was comparable to that of other dinosaurs. There has been debate on whether its head was habitually held downwards, or horizontally like other sauropods. It lived in a

riparian 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 a ...

habitat, and its diet probably consisted of soft plants, such as

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

horsetails ''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of ferns, which reproduce by spores rather than seeds. ''Equisetum'' is a "living fossil", the only living genus of the entire subclass ...

, and

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants ...

. It is one of the most common fossil vertebrates found in the area, and shared its habitat with other dinosaurian megaherbivores, as well as large

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 ...

and

crocodylomorph 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, cro ...

History of discovery

Remains thought to belong to ''Nigersaurus'' were first discovered during a 1965–1972 expedition to the

Republic of Niger ) , official_languages = , languages_type = National languagesPhilippe Taquet, and first mentioned in a paper published in 1976. Although a common genus, the dinosaur had been poorly known until more material of other individuals was discovered during expeditions led by American palaeontologist

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 ...

in 1997 and 2000. The limited understanding of the genus was the result of poor preservation of its remains, which arises from the delicate and highly

pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and ...

construction (filled with air spaces connected to

) of the skull and skeleton, in turn causing disarticulation of the fossils. Some of the skull fossils were so thin that a strong light beam was visible through them. Therefore, no intact skulls or articulated skeletons have been found, and these specimens represent the most complete known rebbachisaurid remains. ''Nigersaurus'' was named and described in more detail by Sereno and colleagues only in 1999, based on remains of newly found individuals. The same article also named ''

Jobaria ''Jobaria'' is a genus of sauropod dinosaur that lived in what is now Niger during the middle Jurassic Period, between 164 and 161 million years ago. ''Jobaria'' is currently the only known valid sauropod from the Tiouraren, where it was disc ...

'', another

from Niger. The genus name ''Nigersaurus'' ("Niger reptile") is a reference to the country where it was discovered, and the specific name ''taqueti'' honours Taquet, who was the first to organise large-scale palaeontological expeditions to Niger. 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 seve ...

specimen (MNN GAD512) consists of a partial skull and neck. Limb material and a

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 ...

(shoulder blade) found nearby were also referred to the same specimen. These fossils are housed at the National Museum of Niger. Nigersaurus taqueti skeleton

Sereno and the American palaeontologist Jeffrey A. Wilson provided the first detailed description of the skull and feeding adaptations in 2005. In 2007, a more detailed description of the skeleton was published by Sereno ad colleagues, based on a specimen discovered ten years earlier. The fossils, along with a reconstructed skeleton mount and a plastic model of the head and neck, were subsequently presented at the

National Geographic Society The National Geographic Society (NGS), headquartered in Washington, D.C., United States, is one of the largest non-profit scientific and educational organizations in the world. Founded in 1888, its interests include geography, archaeology, ...

in Washington. ''Nigersaurus'' was dubbed a "

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

cow" in the press, and Sereno stressed that it was the most unusual dinosaur he had ever seen. He likened its physical appearance to

Darth Vader Darth Vader is a fictional character in the ''Star Wars'' franchise. The character is the central antagonist of the original trilogy and, as Anakin Skywalker, is one of the main protagonists in the prequel trilogy. ''Star Wars'' creator George ...

and a

vacuum cleaner A vacuum cleaner, also known simply as a vacuum or a hoover, is a device that causes suction in order to remove dirt from floors, upholstery, draperies, and other surfaces. It is generally electrically driven. The dirt is collected by either a ...

, and compared its tooth shear with a

conveyor belt A conveyor belt is the carrying medium of a belt conveyor system (often shortened to belt conveyor). A belt conveyor system is one of many types of conveyor systems. A belt conveyor system consists of two or more pulleys (sometimes referred t ...

and sharpened piano keys. Numerous ''Nigersaurus'' specimens collected by French and American expeditions remain to be described. Teeth similar to those of ''Nigersaurus'' have been found on the

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Is ...

and in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, but it is unknown whether they belonged to relatives of this

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

, or to titanosaurs, whose remains have been found in the vicinity. A lower jaw assigned to the titanosaur ''

Antarctosaurus ''Antarctosaurus'' (; meaning "southern lizard") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. The type species, ''Antarctosaurus wichmannianus'', and a second species, ''Antarc ...

'' is likewise similar to that of ''Nigersaurus'', but may have evolved convergently.

Description

Like all sauropods, ''Nigersaurus'' was a

quadruped Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...

with a small head, thick hind legs, and a prominent tail. Among that

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 ter ...

, ''Nigersaurus'' was fairly small, with a body length of only and a

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 ...

reaching only ; it may have weighed around , comparable to a modern

. It had a short neck for a sauropod, with thirteen

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

. Nearly all

s had relatively short necks and a length of or less. The only members of the family that reached the size of larger sauropods were ''

Rebbachisaurus ''Rebbachisaurus'' (meaning "Khebbash, Aït Rebbach lizard") is a genus of sauropod dinosaur of the superfamily Diplodocoidea, that lived during the Late Cretaceous period in Africa and possibly also South America about 99-97 million years ago. R ...

'' and ''

Maraapunisaurus ''Maraapunisaurus'' is a genus of sauropod dinosaur from the Late Jurassic Morrison Formation of western North America. It is known only from what has sometimes been estimated to be the largest dinosaur specimen ever discovered, originally name ...

''.

Skull

The skull of ''Nigersaurus'' was delicate, with the four side

fenestra A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...

e (openings in the skull) larger than in other

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

s. The total area of bone connecting the muzzle to the back of the skull was only . These connecting struts of bones were usually less than thick. Despite this, the skull was resistant to the sustained shearing of the teeth. Another unique trait it had among sauropodomorphs was a closed

supratemporal fenestra The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

. The nasal openings, the bony nostrils, were elongated. Though the nasal bones are not completely known, it appears the front margin of the bony nostril was closer to the snout than in other diplodocoids. The snout was also proportionately shorter, and the tooth row was not at all

prognathous Prognathism, also called Habsburg jaw or Habsburgs' jaw primarily in the context of its prevalence amongst members of the House of Habsburg, is a positional relationship of the Human mandible, mandible or maxilla to the skeletal base where eithe ...

, the snout tip not protruding relative to the remainder of the tooth series. ''Nigersaurus'' was distinct in that its (which formed much of the skull-roof) was elongate (much narrower than long), and had a marked cerebral fossa (a depression on the surface of this bone inside the head). The maxillary tooth row was in its entirety transversely rotated, its normal rear 90° everted towards the front. This was matched by an identical rotation of the dentary of the lower jaw. This transverse orientation of the upper and lower tooth rows was unique to the dinosaur. Due to this configuration, no other tetrapod had all of its teeth located as far to the front as ''Nigersaurus''. Nigersaurus teeth

The slender teeth had slightly curved

tooth crowns In dentistry, crown refers to the anatomical area of teeth, usually covered by enamel. The crown is usually visible in the mouth after developing below the gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tiss ...

, which were oval in cross-section. The crowns were distinct in having prominent ridges on the margins of their midline and sides. The teeth in the lower jaw may have been 20–30% smaller than those in the upper jaw, but few are known, and they are of uncertain maturity. Apart from this, the teeth were identical. Under each active tooth there was a column of nine replacement teeth within the jaw. With 68 columns in the upper jaws and 60 columns in the lower jaws, these so-called dental batteries (also present in

hadrosaur 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 includ ...

s and

ceratopsian Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

s) comprised a total of more than 500 active and replacement teeth. Dental batteries erupted in unison, not each column individually. The enamel on the teeth of ''Nigersaurus'' was highly asymmetrical, ten times thicker on the outwards facing side than on the inner side. This condition is otherwise known only in advanced

ornithischians 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 ...

. ''Nigersaurus'' did not exhibit the same modifications seen in the jaws of other dinosaurs with dental batteries, or mammals with elaborate chewing functions. The

lower jaw In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

was L-shaped and divided into the subcylindrical transverse

ramus Ramus can refer to: * A branch (botany) * A portion of a bone (from Latin ''ramus'', "branch"), as in the Ramus of the mandible or Superior pubic ramus * A nerve ramus such as the Dorsal ramus of spinal nerve * A taxonomic rank ("branch" in English ...

, which contained the teeth, and the back ramus, which was more lightweight and was the location for most of the muscle attachments. It was distinct in that the tooth row expanded to the sides from the plane of the main ramus of the lower jaw. The jaws also contained several fenestrae, including five that are not present in other sauropods. The front ends of the jaws had grooves that indicate the presence of a keratinous (horny) sheath. ''Nigersaurus'' is the only known tetrapod animal to have had jaws wider than the skull and teeth that extended laterally across the front. The snout was even broader than those of the "duck-billed" hadrosaurs.

Postcranial skeleton

''Nigersaurus'' was distinct in that its (back) vertebrae had paired pneumatic spaces at the base of the (the spines that projected upwards from the vertebrae). The presacral vertebrae (vertebrae in front of the

sacrum 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 ...

) were heavily pneumatised to the point where the column consisted of a series of hollow "shells", each divided by a thin

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

in the middle. It had little to no

cancellous bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...

, making the

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different f ...

thin bone plates filled with air spaces. The

vertebral arch 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 i ...

es were so heavily pierced by extensions of the external air sacs that of their side walls little remained but thick intersecting laminae, the ridges between the pneumatic openings. The vertebrae of the tail, however, did have solid centra. The

pelvic 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 ...

and

pectoral 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 of t ...

bones were very thin also, often only several millimetres thick. It had a prominent rugosity (a roughly wrinkled area) on the midline aspect of the scapular blade's base, a distinguishing feature. Like other sauropods, its limbs were robust, contrasting with the extremely lightweight construction of the rest of the skeleton. The limbs were not as specialised as the rest of the skeleton, and the front legs of ''Nigersaurus'' were about two-thirds the length of the back legs, as in most

diplodocoid Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like ''Supersaurus'', ''Diplodocus'', ''Apatosaurus'', and ''Amphicoelias''. Most had very long necks and long, ...

s..

Classification

The remains of ''Nigersaurus'' were initially described by Taquet in 1976 as belonging to a

dicraeosaurid Dicraeosauridae is a family of diplodocoid sauropods who are the sister group to Diplodocidae. Dicraeosaurids are a part of the Flagellicaudata, along with Diplodocidae. Dicraeosauridae includes genera such as ''Amargasaurus'', ''Suuwassea'', ' ...

, but in 1999 Sereno and colleagues reclassified it as a rebbachisaurid diplodocoid. These researchers speculated that since short necks and small size was known among basal diplodocoids, it may indicate these were ancestral features of the group. Rebbachisauridae is the

basalmost In phylogenetics, basal is the direction of the ''base'' (or root) of a rooted phylogenetic tree or cladogram. The term may be more strictly applied only to nodes adjacent to the root, or more loosely applied to nodes regarded as being close to th ...

family within the superfamily Diplodocoidea, which also contains the long-necked

diplodocid Diplodocids, or members of the family Diplodocidae ("double beams"), are a group of sauropod dinosaurs. The family includes some of the longest creatures ever to walk the Earth, including ''Diplodocus'' and ''Supersaurus'', some of which may have ...

s and the short-necked dicraeosaurids. The

subfamily

Nigersaurinae Rebbachisaurinae is a subfamily within the family Rebbachisauridae, defined to include ''Rebbachisaurus garasbae'' and exclude '' Limaysaurus tessonei''. It was first proposed as a rank by Jose Bonaparte Jose is the English transliteration of ...

, which includes ''Nigersaurus'' and closely related genera, was named by the American palaeontologist John A. Whitlock in 2011. The closely related genus ''

Demandasaurus ''Demandasaurus'' (meaning " Demanda lizard") is a genus of rebbachisaurid sauropod dinosaur from early Cretaceous (late Barremian – early Aptian stage) deposits of Spain. ''Demandasaurus'' is known from an incomplete but associated skeleton th ...

'' from Spain was described by the Spanish palaeontologist Fidel Torcida Fernández-Baldor and colleagues in 2011, and along with other animal groups that span the Cretaceous of Africa and Europe, this indicates that carbonate platforms connected these landmasses across the

Tethys Sea The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

. This was supported in 2013 by the Italian palaeontologist Federico Fanti and colleagues in their description of the nigersaurine ''

Tataouinea ''Tataouinea'' is an extinct genus of sauropod dinosaur in the subfamily Rebbachisaurinae of Rebbachisauridae which lived in the Early Cretaceous of Tunisia. Only one species, ''T. hannibalis'', is known. Discovery and naming The first kn ...

'' from Tunisia, which was more related to the European form than to ''Nigersaurus'', despite being from Africa, then part of the supercontinent

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

. Pneumatisation of the rebbachisaurid skeleton evolved progressively, culminating in the nigersaurines. Nigersaurus taqueti skeletal

Below is a

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 ...

following the 2013 analysis by Fanti and colleagues, which confirmed the placement of ''Nigersaurus'' as a basal nigersaurine rebbachisaurid. A 2015 cladistic study by Wilsona and the French palaeontologist Ronan Allain found ''Rebbachisaurus'' itself to group with the nigersaurines, and the authors suggested that Nigersaurinae was therefore a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

of Rebbachisaurinae (since that name would have priority). The same year, Fanti and colleagues supported the use of Rebbachisaurinae over Nigersaurinae, and found ''Nigersaurus'' to be the basalmost member of this "Euro-African" subclade. In 2019, Mannion and colleagues pointed out that since ''Nigersaurus'' was found to be the sister taxon of all other nigersaurines in some studies, a Rebbachisaurinae clade may not necessarily include ''Nigersaurus'' itself (as well as the fact that the position of ''Rebbachisaurus'' could change in future analyses), and supported the continued use of the name Nigersaurinae over Rebbachisaurinae for all rebbachisaurids more closely related to ''Nigersaurus'' than to ''Limaysaurus''. They found that nigersaurines were restricted to North Africa and Europe, and that Limaysaurinae was strictly known from Argentina. The same year, the Brazilian palaeontologist Rafael Matos Lindoso and colleagues used the name Nigersaurinae following Mannion's recommendation, and found '' Itapeuasaurus'' from Brazil to group with the nigersaurines, thereby expanding this lineage more widely (making palaeobiogeographic hypotheses for this group less reliable).

Palaeobiology

Though it had large nostrils and a fleshy snout, Sereno and colleagues found that ''Nigersaurus'' had an underdeveloped olfactory region of its brain and thus did not have an advanced sense of smell. Its brain-to-body-mass ratio was average for a reptile, and smaller than those of ornithischians and non- coelurosaurian

theropod 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 c ...

s. The

cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...

comprised about 30% of the brain volume, as in many other dinosaurs. The American

palaeoartist Paleoart (also spelled palaeoart, paleo-art, or paleo art) is any original artistic work that attempts to depict prehistoric life according to scientific evidence. Works of paleoart may be representations of fossil remains or imagined depiction ...

Mark Hallett and paleontologist Mathew J. Wedel and stated in 2016 that while sauropods in general could use their long necks to detect predators from afar, this would not apply to the short-necked ''Nigersaurus''. They pointed out that the eyes of ''Nigersaurus'' were placed further towards the top of the skull than in most other sauropods, above the muzzle, which would give it overlapping fields of view. Its visual field would have been at or close to 360 degrees, and hypersensitivity of movement would have been important to a vulnerable prey-animal. In 2017, the Argentinian palaeontologist Lucio M. Ibiricu and colleagues examined the postcranial skeletal pneumaticity in the skeletons of rebbachisaurids, and suggested that it was an adaptation for lowering the density of the skeleton, and that this could have decreased the muscle energy needed to move the body, as well as the heat generated in the process. Since several rebbachisaurids inhabited latitudes that would have been tropical to subtropical in the Middle Cretaceous, this pneumaticity may have helped the animals cope with the very high temperatures. According to Ibiricu and colleagues, this adaptation may be a reason why rebbachisaurids were the only group of diplodocoids that survived into the Late Cretaceous.

Diet and feeding

''Nigersaurus'' was suggested by Sereno and colleagues to be a ground-level, non-selective browser. The width of the muzzle and lateral orientation of the tooth row show that the sauropod could gather much food and crop it close to the ground, within of the surface. This is further supported by

facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cut ...

s on the labial (externally facing) side of the upper teeth, similar to ''

Dicraeosaurus ''Dicraeosaurus'' (Gr. , ' "bifurcated, double-headed" + Gr. , ' "lizard") is a genus of diplodocoid sauropod dinosaur that lived in what is now Lindi Region, Tanzania during the late Jurassic period. The genus was named for the neural spines on ...

'' and ''

Diplodocus ''Diplodocus'' (, , or ) was a genus of diplodocid sauropod dinosaurs, whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a neo-Latin term derived from Greek διπ� ...

'', which are evidence that food or substrate wore the animal's teeth as it fed. ''Nigersaurus'' also bears signs of low-angle tooth-to-tooth wear on the inside of the maxillary crowns, which suggests that jaw movement was limited to precise up-and-down motions. Worn teeth from the lower jaw have not yet been discovered, but they are expected to show opposing tooth-to-tooth wear. The ability to raise their heads well above the ground does not necessarily mean they browsed on items there, and the short neck of ''Nigersaurus'' would have restricted the browsing range compared to other diplodocoids. The adductor muscle of the jaw appears to have attached to the quadrate instead of the supratemporal fenestra. Both this and the other mastication muscles were likely weak, and ''Nigersaurus'' is estimated to have had one of the weakest bites of the sauropods. In addition, according to Whitlock and colleagues in 2011, the small, nearly parallel nature of the tooth scratches and pits (caused by grit, which would not be obtained as often by high-browsers) indicate that it ate relatively soft,

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...

plants such as low-growing ferns. Because of the lateral orientation of the teeth, it probably would not have been able to chew. ''Nigersaurus'' wore its tooth crowns down faster than other dinosaurian herbivores, and its tooth replacement rate was the highest of any known dinosaur. Each tooth was replaced once every 14 days; the rate had previously been estimated lower. In contrast to ''Nigersaurus'', sauropods with lower tooth replacement rates and broader tooth crowns are thought to have been

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

browsers. Grass did not evolve until the late Cretaceous, making

, and

(which had evolved by the middle Cretaceous) potential food for ''Nigersaurus''. Sereno and colleagues stated it was unlikely that ''Nigersaurus'' fed on

conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extan ...

cycads Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or ...

, or

aquatic vegetation Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...

, due respectively to their height, hard and stiff structure, and lack of appropriate habitat. Wedel suggested that the evenly spaced teeth of ''Nigersaurus'' could have functioned like a comb, by straining water plants or invertebrates, similar to

flamingos Flamingos or flamingoes are a type of wading bird in the family Phoenicopteridae, which is the only extant family in the order Phoenicopteriformes. There are four flamingo species distributed throughout the Americas (including the Caribbean) ...

. He also suggested it could have low-browsed from short conifers and other low-growing plants. Nigersaurus taqueti skull

Head posture

On the basis of

microtomography X-ray microtomography, like tomography and X-ray computed tomography, uses X-rays to create cross-sections of a physical object that can be used to recreate a virtual model (3D model) without destroying the original object. The prefix ''micro-'' ...

scans of skull elements of the holotype specimen, Sereno and colleagues created a "

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...

" ''Nigersaurus'' skull they could examine. They also made an

endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...

of the brain and scanned the

semicircular canals The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals. Structure The ...

of its

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

, which they found to be oriented horizontally. In their 2007 study, they stated that the structure of the

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...

and cervical vertebrae would have limited the upward and downward movement of the neck and the rotation of the skull. Based on this biomechanical analysis, the team concluded that the head and muzzle were habitually oriented 67° downwards and close to ground level, as an adaptation for ground-level browsing. This is unlike the way other sauropods have been restored, with their heads held more horizontally. A 2009 study by the British palaeontologist

Mike P. Taylor Michael Paul Taylor (born 12 March 1968) is a British computer programmer with a Ph.D. in palaeontology. To date, he has published 18 paleontological papers and is co-credited with naming three genera of dinosaur ('' Xenoposeidon'' in 2007 with D ...

and colleagues agreed that ''Nigersaurus'' was able to feed with the downturned head and neck posture proposed by the 2007 study, but contested that this was the habitual posture of the animal. The study noted that the "neutral" head and neck posture of modern animals does not necessarily correspond to their habitual head posture. It further argued that the orientation of the semicircular canals varies significantly within modern species, and is therefore not reliable for determining head posture. This was supported by the Spanish palaeontologist Jesús Marugán-Lobón and colleagues in a 2013 study that suggested the methods used by Sereno's team were imprecise, and that ''Nigersaurus'' habitually held its head like other sauropods. In 2020, the French palaeontologist Julien Benoit and colleagues tested lateral semicircular canal correlation to head posture on modern mammals, and found that while there was significant correlation between the reconstructed and actual head postures, the plane of the semicircular canal was not held horizontally in the resting pose as inferred. The authors therefore cautioned against using semicircular canals as proxy to infer the precise orientation of skulls. They found that diet correlated strongly with semicircular canal orientation, but not with head posture, while head posture and semicircular canal orientation were strongly correlated with phylogeny.

Palaeoenvironment

''Nigersaurus'' is known from the

of the Tegama Group in an area called Gadoufaoua, located in Niger. It is one of the most commonly found vertebrates in the formation. 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. ''Nigersaurus'' lived in what is now Niger about 115 to 105 million years ago, 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 ...

and

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

ages of the mid-Cretaceous. 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'' was the most numerous megaherbivore. Other herbivores from the same formation include ''

Ouranosaurus ''Ouranosaurus'' is a genus of herbivorous basal hadrosauriform dinosaur that lived during the Aptian stage of the Early Cretaceous of modern-day Niger and Cameroon. ''Ouranosaurus'' measured about long. Two rather complete fossils were found in ...

'', ''

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

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 ''Suchomimus'' (meaning "crocodile mimic") is a genus of spinosaurid dinosaur that lived between 125 and 112 million years ago in what is now Niger, during the Aptian to early Albian stages of the Early Cretaceous period. It was named and ...

'', and ''

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 ...

'', and a yet-unnamed

noasaurid Noasauridae is an extinct family of theropod dinosaurs belonging to the group Ceratosauria. They were closely related to the short-armed abelisaurids, although most noasaurids had much more traditional body types generally similar to other ther ...

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 ''

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 ...

'', ''

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

'', ''

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 Turtles are an order (biology), order of reptiles known as Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) an ...

, 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 shark ...

shark, and freshwater bivalves have been found.

References

External links

National Geographic Live! – Extreme Dinosaurs – lecture about the discovery of ''Nigersaurus'' by Paul Sereno

National Geographic Live! – Bringing Back ''Nigersaurus'' – video about the reconstruction of a ''Nigersaurus'' skeleton
{{Taxonbar, from1=Q18511062, from2=Q131407 Rebbachisaurids Albian life Aptian life Early Cretaceous dinosaurs of Africa Cretaceous Niger Fossils of Niger Fossil taxa described in 1999 Taxa named by Paul Sereno