''Spinophorosaurus'' 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 ...

of sauropod

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 in what is now

Niger ) , official_languages = , languages_type = National languagesMiddle Jurassic period. The first two specimens were excavated in the 2000s by German and Spanish teams under difficult conditions. The skeletons were brought to Europe and digitally replicated, making ''Spinophorosaurus'' the first sauropod to have its skeleton

3D printed 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...

, and were to be returned to Niger in the future. Together, the two specimens represented most of the skeleton of the genus, and one of the most completely known basal sauropods of its time and place. The first skeleton was made the

holotype specimen 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 ...

of the new genus and species ''Spinophorosaurus nigerensis'' in 2009; the generic name ("spine-bearing lizard") refers to what was initially thought to be spiked

osteoderms 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 amphi ...

, and the specific name (Niger and -ensis) refers to where it was found. A juvenile sauropod from the same area was later assigned to the genus. The subadult holotype specimen is estimated to have been around in length, whereas the

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

was about long. The shoulder height reached by these individuals was estimated at around , and the weight at about . The braincase was short, deep, and broad, and the

neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

was in some ways intermediate between that of basal

sauropodomorphs 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 ...

and the more derived neosauropods. The teeth were spatulate (spoon shaped) and had large spaced denticles at the top of the crown, an ancestral feature in sauropods. The neck of ''Spinophorosaurus'' is one of the most completely known among sauropods, containing 13 . The dorsal vertebrae had multiple small air-filled internal chambers, a feature typical of later more-derived sauropods. The tail was powered by strong musculature and had a rear section that was rather rigid due to long and overlapping chevron bones. Bones originally thought to be osteoderms bearing spikes placed on the tail tip were later suggested to be . ''Spinophorosaurus'' has been classified as either a very basal sauropod, or inside

Eusauropoda Eusauropoda (meaning "true sauropods") is a derived clade of sauropod dinosaurs. Eusauropods represent the node-based group that includes all descendant sauropods starting with the basal eusauropods of ''Shunosaurus'', and possibly ''Barapasaur ...

, a more derived group. The anatomy, age, and location of specimens indicate that important developments in sauropod evolution may have occurred in

North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...

, possibly controlled by climatic zones and plant biogeography. Features of the

vestibular apparatus The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...

suggest that vision and coordinated eye, head, and neck movements were important in ''Spinophorosaurus''. 3D models of the skeleton have been used to test its range of motion. One study suggests it may have been a high browser, and another examined possible mating postures. Sutures between the neural arches with the centra of the vertebrae were more complex in the front part of the trunk of ''Spinophorosaurus'', since stresses were probably greatest in that region. ''Spinophorosaurus'' is known from the Irhazer Shale, a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

thought to be Middle Jurassic in age. It was formed by deposits from rivers and lakes in a great river-valley system.

Discovery

The rich dinosaur fauna of

Niger ) , official_languages = , languages_type = National languagesgenera from

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eig ...

rocks, most prominently the

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 ''

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 ...

''. An older succession of rocks, the Tiourarén Formation, was explored 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 sites ...

, who conducted a large-scale excavation campaign in Niger between 1999 and 2003. Although initially thought to fall within the Lower Cretaceous, the formation is now thought to be of a much older Middle Jurassic age. Sereno named new dinosaurs such as the sauropod '' Jobaria'' and the

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 ...

Afrovenator ''Afrovenator'' (; "African hunter") is a genus of megalosaurid theropod dinosaur from the Middle Jurassic Period of northern Africa. Discovery and naming The remains of ''Afrovenator'' were discovered in 1993 in the Tiourarén Formation ...

'' from the Tiourarén; most finds were discovered along a cliff known as the ''Falaise de Tiguidit'' in the southern

Agadez Region Agadez Region is one of the seven regions of Niger. At , it covers more than half of Niger's land area, and is the largest region in the country, as well as the largest African state subdivision. The capital of the department is Agadez. Histo ...

. In Marendet, Sereno left partial ''Jobaria'' skeletons in the field as a tourist attraction. Starting in 2003, the PALDES project (''Paleontología y Desarrollo'' – "Palaeontology and development") was conducting excavations in the southern Agadez Region. A cooperative effort between Spanish science and humanitarian institutions, PALDES aimed to combine palaeontological research with a developmental program for the region. This included the improvement of infrastructure, education structures, and the promotion of tourism, including the planned construction of a new palaeontological museum in Tadibene. Early in 2005, German explorers Ulrich Joger and Edgar Sommer explored the semi-deserts south of Agadez after local

Tuaregs 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 ...

had informed Sommer about the occurrence of large bones in the region. Sommer is the founder of CARGO, a relief organisation specialised in improving the local education system for the Tuareg people, while Joger is a biologist and the director of the State Natural History Museum, Braunschweig, Germany. On their return route, they chatted with a group of Tuaregs who then directed them to a hilly area nearby that was littered with small bone fragments. This locality (where dinosaurs had not been excavated before) is about north of the ''Falaise de Tiguidit'' and near the town of

Aderbissinat Aderbissinat is a town and commune in central Niger. As of 2011, the commune had a total population of 27,523 people. It lies in the Sahel, the semi-arid, sparsely populated zone between the Sahara Desert to the north and the millet-growing sav ...

in the Agadez Region, and part of the Irhazer Shale (or ''Argiles de l'Irhazer''), a

below (and thus slightly older than) the Tiourarén. After a one-hour search, Joger discovered a rounded bone tip sticking out of the surface, which after further excavation turned out to be a complete

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 wit ...

(thigh bone) of what would later become the

of ''Spinophorosaurus''. An associated

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) and a were discovered soon after. The

sediment 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, sa ...

in the locality, a hard but brittle siltstone, could be removed from the bones using light hammer blows. Spinophorosaurus digsite

Joger and Sommer then hired local Tuaregs for support and, after two days, had uncovered most of the specimen, which included a virtually complete, articulated vertebral column and several limb and pelvic bones. The vertebral column formed an almost complete circle, the tip of the tail being located where the skull would be expected but was not found. Lacking equipment and an excavation permit, they covered the specimen with debris for protection and returned to Germany, now planning a full-scale scientific excavation to be carried out by the Braunschweig museum. An official excavation permit was promised to the museum in 2006 by the Republic of the Niger; in return, the museum was to build and equip a new school for local Tuareg children in the settlement of Injitane. In the autumn of 2006, Sommer and Joger, together with other associates of the Braunschweig museum, revisited the site in preparation for the excavation, putting one of the pelvic bones in plaster to test equipment and methodology. The team also discovered theropod tracks around from the site. Sponsors for financing both the school and excavation were found early in 2007. The official campaign, dubbed "Projekt Dino", started on March 1, 2007, when two trucks with equipment left Braunschweig for Niger, taking a route via Spain, Morocco, Mauritania, and Mali (the shorter route through the Sahara was not possible due to the risk of terrorist attacks). The other part of the team, which comprised ten permanent members, arrived by airplane. It was the first German dinosaur expedition to Africa in almost a century. In the meantime, the Spanish project PALDES team, led by the Palaeontological Museum of Elche, was working in the region. Early in 2007, Mohamed Echika, mayor of Aderbissinat, allowed the PALDES team to excavate the skeleton previously discovered by the Germans; the skeleton was subsequently shipped to Spain. Unaware of these activities, the vanguard of the German team found an empty dig site (showing signs of a professional excavation) upon their arrival on March 16; the trucks arrived on March 20. Although disappointed, the German team discovered a second ''Spinophorosaurus'' specimen, the future

, apart from the first, on March 17. An exploratory trench within an area littered with small bone fragments soon revealed jaw and tooth fragments; on the next day, ribs, vertebrae, a humerus (upper arm bone) and a scapula could be identified. Eight local excavation helpers joined the group on March 19. On March 20, before the arrival of the trucks, the freshwater reserve of initially was depleted as the local helpers had used it for washing the night before, causing members of the team to faint. Excavation was usually interrupted between 12:00 and 15:00 when temperatures reached . On March 25, all but two of the German team members were ill, suffering

diarrhoea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...

and circulation problems. Throughout the excavation, progress was documented with photographs and field notes.

By March 27, the humerus, scapula, and most ribs of the future paratype had already been wrapped in protective plaster and extracted. Although no further bones were apparent beneath the skeleton, the team removed an additional of sediment to make sure that all fossils had been collected. Excavation was completed on April 2, and the fossils were packed for transport to the port of Cotonou on April 3. On the same day, Echika revealed to the team that the first skeleton had been excavated by a Spanish group with his permission. He promised to lead the team to another fossil site located around south of Agadez at the cliff of Tiguidit as compensation. There the team found the rear part of a possible ''Jobaria'' skeleton, but was forced to leave the largest block in the field until the next season. To discourage others from collecting the block, an explosive dummy was fabricated and attached to the fossil, labeled with a warning in Spanish. The German team retrieved the block the next season in 2008; the PALDES team had canceled their excavation plans for that year following the outbreak of the

Tuareg rebellion (2007–2009) The Tuareg Rebellion of 2007–2009 was an insurgency that began in February 2007 amongst elements of the Tuareg people living in the Sahara desert regions of northern Mali and Niger. It is one of a series of insurgencies by formerly nomadic Tu ...

The two ''Spinophorosaurus'' specimens were provisionally housed in the Spanish and German museums. By contract with the Republic of the Niger, they were to be returned to the country in the future, managed by the Musée National d'Histoire Naturelle 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 dis ...

as well as by a smaller, newly built local museum. The future paratype specimen arrived in Germany on March 18, 2007; for its preparation, which took two and a half years, the Braunschweig museum rented a separate factory building. In parallel, a joint paper was prepared by the now cooperating German and Spanish teams. The German team digitised prepared bones and fragments of both specimens in 3D using laser scanning. As the skeleton in Braunschweig was only 70% complete, the specimen in Spain was used to fill in the missing pieces; during this process, it was discovered that the skeleton in Spain was the one the Germans had initially discovered and lost. The 3D scans were digitally repaired and undeformed, printed in 3D, and assembled into a mounted skeleton for the Braunschweig museum's exhibition (the first sauropod skeleton reproduced through 3D-printing). A life-sized model of a living ''Spinophorosaurus'', nicknamed "Namu" (after the museum's name), was put up in front of the main entrance of the museum. The Spanish team produced separate 3D models from photographs of the holotype using photogrammetry (where photos are taken of an object from different angles to map them); a caudal vertebra was put on display at the Elche museum in 2018. In a 2018 conference abstract, García-Martínez and colleagues announced that they reconstructed the morphology of the second back vertebrae, which is poorly preserved, based on the better preserved first and fifth back vertebrae. This was done using landmark-based geometric morphometrics, where corresponding 3D-coordinates are collected from each vertebra and analysed statistically. The first skeleton (divided between the Elche museum, where it was catalogued as GCP-CV-4229, and the Braunschweig museum, catalogued as NMB-1699-R) was made the holotype of the new genus and species ''Spinophorosaurus nigerensis'' by German palaeontologist Kristian Remes and colleagues of the German and Spanish teams in 2009. The generic name is composed of ''spina'', Latin for "spike"; ', Greek for "to bear"; and ''sauros'', which means lizard ("spine-bearing lizard" in full): the name refers to what was initially interpreted as

bearing spikes, which were later suggested to represent instead. The specific name refers to Niger, where the

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 ...

was discovered. The holotype specimen consists of a , a

postorbital bone The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some v ...

, a

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

, a , a

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medi ...

, a

surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular. It is often a mu ...

, and a nearly complete

postcranial skeleton Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

, which lacks the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

, antebrachium, manus, and pes. The second, paratype specimen (NMB-1698-R), consists of a partial skull and an incomplete postcranial skeleton. Elements preserved in this specimen but not the holotype include a

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

, lacrimal,

dentary 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 ...

, angular, the dorsal ribs of the right side, the humerus, and a pedal phalanx. The two specimens are considered to belong to the same taxon since the skeletal elements that overlapped between them were identical, and because of the proximity of the skeletons in the same stratigraphic layer. At the time it was described, ''Spinophorosaurus'' was the most completely known Middle Jurassic sauropod from North Africa, and by 2018 was considered to be one of the most complete early (non-

neosauropod Neosauropoda is a clade within Dinosauria, coined in 1986 by Argentina, Argentine paleontologist José Bonaparte and currently described as ''Saltasaurus loricatus'', ''Diplodocus longus'', and all animals directly descended from their most recen ...

) sauropods. Spinophorosaurus juvenile vertebrae

In 2012, Adrián Páramo and Francisco Ortega from the PALDES team reported a small sauropod skeleton (specimen GCP-CV-BB-15) that had been discovered on the ground, a few metres from the two ''Spinophorosaurus'' specimens; all the fossils were probably from the same beds. The small skeleton consists of 14 vertebrae (some articulated), including all neck vertebrae as well as some back vertebrae. The centra of its vertebrae are 20% smaller than those of ''Spinophorosaurus'' and the neurocentral suture is open, indicating it is a juvenile. Several distinct features of the skeleton are shared with ''Spinophorosaurus'', and though some features of that genus are not present, it most likely represents a juvenile ''Spinophorosaurus'' (the differences probably explained by

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the s ...

, changes during growth).

Description

The holotype specimen was around in length when measured along the vertebral column, while the paratype was about 13 percent larger, measuring around . A 3D photogrammetry model of the holotype skeleton measures from head to tail, the proportions differing from estimates based on 2D skeletal reconstructions. The shoulder height reached by these individuals was estimated at around , and the weight at about . The holotype specimen's endocranial and neurocentral sutures in the skull and vertebrae respectively are unfused, indicating it was a subadult, whereas the paratype specimen has fully fused neurocentral sutures. In 2020, Vidal and colleagues revised the posture of ''Spinophorosaurus'', based on the mounting of the digital skeleton. While the original 2009 skeletal reconstruction showed the dinosaur with a horizontal posture, the digital reconstruction showed a more vertical posture, with tall shoulders and an elevated neck. One of the features pointed out by these researchers that would have made the pose of this dinosaur more vertical was that the vertebrae of the sacrum and the hindmost back vertebrae were wedged, causing the vertebral column to be deflected upwards toward the front of the sacrum at an angle of 10°. Additional features that made the posture more vertical were the elongated scapulae and humeri, as well as elongated facets on the neck vertebrae and a specialised first back vertebra. Consequently, the snout of ''Spinophorosaurus'' would have been held about above the ground, more than twice the height of the shoulders and acetabulum where the hindlimb attached to the pelvis, which were at a height of .

Skull

The frontal bones of the were fused in the midline, unlike the other sutures of the skull. Between the frontals was a small , about in front of the suture between the frontal and the parietal bones. The rear margin of the skull had an open postparietal notch, a feature otherwise only known in

dicraeosaurids Dicraeosauridae is a Family (biology), family of Diplodocoidea, diplodocoid sauropods who are the sister group to Diplodocidae. Dicraeosaurids are a part of the Flagellicaudata, along with Diplodocidae. Dicraeosauridae includes genera such as ''A ...

and '' Abrosaurus''. A notch following the midline at the front of the conjoined frontal bones indicates there might have been a prong extending from each nasal bone to between the frontals, as may have been the case for ''

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 ...

'' but is unusual among sauropods in general. The upper temporal fenestrae, a pair of major openings on the skull roof, were four times broader than long; such broadened fenestrae were typical for ''Shunosaurus'' and more derived (or "advanced") sauropods. The

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...

at the back of the skull was concave on the sides, like in ''

Shunosaurus ''Shunosaurus'', meaning "shu lizard", is a genus of sauropod dinosaur from Late Jurassic ( Oxfordian) beds in Sichuan Province in China, approximately 159±2 million years ago. The name derives from "Shu", an ancient name for the Sichuan p ...

''. The (a pair of extensions on the underside of the skull base that served as muscle attachments) were enlarged and were directed to the sides, unique among known sauropods. The quadrate did not have a concavity on the hind-side, an

ancestral An ancestor, also known as a forefather, fore-elder or a forebear, is a parent or ( recursively) the parent of an antecedent (i.e., a grandparent, great-grandparent, great-great-grandparent and so forth). ''Ancestor'' is "any person from wh ...

condition otherwise only known in ''

Tazoudasaurus ''Tazoudasaurus'' is a genus of vulcanodontid sauropod dinosaurs hailing from the Early Jurassic, located in the High Atlas Mountains of Morocco in North Africa. Along with ''Ohmdenosaurus'' is one of the two formally described sauropods from th ...

'' among sauropods. The spatulate (spoon shaped) teeth were unique in possessing enlarged, spaced denticles around the top of the crown, with a higher count of denticles on the front edge of the crown. The braincase of ''Spinophorosaurus'' was broad and short from front to back, moderately deep, and of relatively large size overall. It differed significantly from those of other Jurassic sauropods, possibly except ''

Atlasaurus ''Atlasaurus'' is a genus of sauropod dinosaurs from Middle Jurassic (Bathonian to Callovian stages) beds in North Africa.M. Monbaron, D. A. Russell, and P. Taquet. (1999). ''Atlasaurus imelakei'' n.g., n.sp., a brachiosaurid-like sauropod from ...

''. They shared a on their that were similar in being directed strongly backwards. A CT

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 holotype's brain cavity showed it was similar to most sauropods in having pontine and cerebral flexures that were well marked, a pituitary fossa that was large and oblong, and in that the structure of the brain was obscured by spaces that housed relatively thick meninges as well as by

dural venous sinuses The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous channels found between the endosteal and meningeal layers of dura mater in the brain. They receive blood from the cerebral veins, receive cere ...

. The

labyrinth In Greek mythology, the Labyrinth (, ) was an elaborate, confusing structure designed and built by the legendary artificer Daedalus for King Minos of Crete at Knossos. Its function was to hold the Minotaur, the monster eventually killed by t ...

of the inner ear was characteristic in having long and slender

semicircular canal In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line o ...

s, similar to those of ''

Massospondylus ''Massospondylus'' ( ; from Greek, (massōn, "longer") and (spondylos, "vertebra")) is a genus of sauropodomorph dinosaur from the Early Jurassic. (Hettangian to Pliensbachian ages, ca. 200–183 million years ago). It was described by S ...

'' and ''

Giraffatitan ''Giraffatitan'' (name meaning "titanic giraffe") is a genus of sauropod dinosaur that lived during the late Jurassic Period (Kimmeridgian–Tithonian stages) in what is now Lindi Region, Tanzania. It was originally named as an African species ...

''. Its

was in some ways intermediate between that of basal (or "primitive") sauropodomorphs and the more derived neosauropods.

Vertebrae and ribs

The vertebral column is almost completely known, and the holotype is one of the few sauropod specimens that include a complete neck. The neck was composed of 13 . The trunk had 12 and four . The tail comprised more than 37 . Complex elements, individual vertebrae are composed of a lower part, the , and an upper part, the . Important landmarks of the neural arch include the upwards projecting (spinous process) and the sideward projecting , which together give the vertebra a T-shape in front and rear views. Pairs of connecting with neighboring vertebrae are protruding from the front () and rear (). The cervical vertebrae were similar to those of ''Jobaria'' and ''

Cetiosaurus ''Cetiosaurus'' () meaning 'whale lizard', from the Greek '/ meaning 'sea monster' (later, 'whale') and '/ meaning 'lizard', is a genus of herbivorous sauropod dinosaur from the Middle Jurassic Period, living about 168 million years ago in what ...

''. Their centra were approximately 3.1 times as long as wide; they were therefore moderately elongated compared to sauropods in general, but generally longer than in other basal forms. The cervical centra had large excavations on their sides that deepened towards the front; such were also developed in ''Jobaria'' and ''Patagosaurus''. Unlike in ''Jobaria'', the pleurocoels were not subdivided by an oblique bony ridge. A midline keel was present on the underside of the front end of the centrum, which was absent in ''Cetiosaurus''. The tips of the prezygapophyses had a triangular extension which is also seen in ''Jobaria'', although it is deeper in that genus. Above the postzygapophyses were comparatively large , bony projections for muscle attachment. The cervical vertebrae were different from those of basal sauropods from South America and India. The diapophyses (sideward facing processes of the neural arch) were inclined to face slightly downwards and had triangular flanges on their rear margins—features unseen in those southern forms. Furthermore, the neural spines were rugose (wrinkled) on their rear and front surfaces and close to the base of the neck, broader in side view and less high. In side view, a U-shaped depression was present between the centrum and the neural arch, which is an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

(unique feature) of ''Spinophorosaurus''. Spinophorosaurus in environment modified

The dorsal vertebrae were unusual in having a camellate internal structure (containing multiple small air-filled chambers). This feature is otherwise known in the much later titanosauriforms as well as in

mamenchisaurids Mamenchisauridae is a family of sauropod dinosaurs belonging to Eusauropoda known from the Jurassic and Early Cretaceous of Asia and Africa. Some members of the group reached gigantic sizes, amongst the largest of all sauropods. Classification T ...

, where it evolved independently from the former group. Although the front dorsal vertebrae showed deep pleurocoels in their centra, these openings became much shallower towards the rear of the trunk. The rearmost dorsal vertebrae were also proportionally short. In ''

Amygdalodon ''Amygdalodon'' (; "almond tooth" for its almond shaped teeth) was a genus of basal sauropod from the Middle Jurassic of Argentina. The type species is ''Amygdalodon patagonicus''. Fossils of ''Amygdalodon'' have been found in the Toarcian Cerr ...

'' and ''

Patagosaurus ''Patagosaurus'' (meaning "Patagonia lizard") is an extinct genus of eusauropod dinosaur from the Middle-Late Toarcian of Patagonia, Argentina. It was first found in deposits of the Cañadón Asfalto Formation, which date to around 179 to 177&n ...

'', in contrast, the rearwards dorsals were more elongated and had pronounced pleurocoels. The neural canal of the dorsal vertebrae was very narrow but high. Hyposphene-hypantrum articulations (accessory articular processes) were present in all dorsals, making the spine more rigid. The neural spines had marked rugosities on their front and back sides, as in other basal sauropods. The frontmost caudal vertebrae had the same rugosities on the neural spines as seen in the dorsals, a feature otherwise only known in ''

Omeisaurus ''Omeisaurus'' (meaning "Omei lizard") is a genus of sauropod dinosaur from the Middle Jurassic Period (Bathonian-Callovian stage) of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation o ...

''. In the hind part of the tail, the neural spines were strongly inclined backwards and extended over the front part of the succeeding vertebra, similar to some East Asian sauropods, ''Barapasaurus'', and ''Jobaria''. The ribs of the second to fifth dorsal vertebrae were flattened and backwards directed, while those of the sixth to eleventh dorsal were more circular in cross-section and more vertically oriented. The ribcage can therefore be clearly subdivided into a pectoral and a lumbar section; such a differentiation has only been described in a single other sauropod, the dicraeosaurid ''

Brachytrachelopan ''Brachytrachelopan'' is a short-necked sauropod dinosaur from the Late Jurassic ( Oxfordian to Tithonian) of Argentina. The holotype and only known specimen (Museo Paleontológico Egidio Feruglio MPEF-PV 1716) was collected from an erosion ...

''. Furthermore, the ends of the pectoral ribs had attachment sites for the sternal ribs, which connected to the sternum. In the front part of the tail, the ( bones below the vertebral centra) were blade-like, which is the basal condition. In the rear part of the tail, the chevrons were rod-like, and the left and right counterparts separated from each other. These rod-like chevrons would have been closely attached to the bottom edges of the centra. They articulated with the preceding and succeeding chevrons at the mid length of the vertebral centra, thus bracing the vertebral joint, restricting bending of the tail.

Girdles, limbs, and misidentified tail spikes

The scapula was unique amongst sauropods, being strongly curved with an expanded, fan-shaped lower end. It was D-shaped in cross-section, a feature characteristic for eusauropods. Its upper end was broadened and featured a bony flange on the lower margin. In these respects it was similar to mamenchisaurids from Asia but different from the Gondwanan forms ''Vulcanodon'', ''Barapasaurus'', and ''Patagosaurus'', in which the upper end was only weakly broadened, and the rear flange lacking. The , which articulated to the lower end of the scapula, showed a distinct kidney-shape, considered an autapomorphy. It had a large biceps tubercle to which the biceps brachii muscle attached. The clavicle was robust, although more slender than in ''Jobaria''. Of the forelimb only the humerus is preserved. Its lower end was asymmetrical and had enlarged accessory condyles (forward directed projections on the lower front margin of the bone)—features otherwise only seen in mamenchisaurids. The pubis and ischium of the pelvis were robust, the latter being broadened at its end. The upper femur (thigh bone) was characterised by the presence of a on its upper end—a bony projection serving as attachment site for muscles that drew the hind leg forwards and inwards. The

fourth trochanter The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'' ...

, which projected from the back surface and anchored muscles that drew the hind leg backwards, was especially large in ''Spinophorosaurus''. Close to the fourth trochanter was a large opening that is absent in other sauropods, and thus an autapomorphy. The tibia (shinbone) was similar to that of other basal sauropods, and the fibula (calf bone) was robust. Of the ankle, the upper side of the had facets for articulation with the tibia and fibula that were not separated by a bony wall, and as many as eight (openings that allow blood vessels to enter the bone). Elements originally interpreted as a left and right osteoderm (bone formed in the skin) were found with the holotype skeleton. These bones had a roundish base from which a spike-like projection protruded; the inner surfaces were rugose and concave. Although found within the pelvic region, Remes and colleagues thought they were situated on the tip of the tail in the living animal, which they considered a distinguishing feature of the genus. This position was based on the fact that the left and right elements were found closely together, suggesting they came from near the midline of the body. Furthermore, the stiffening of the hind part of the tail by elongated chevrons is also observed in other dinosaurs showing tail clubs or spikes. Similar spines were part of a tail club in the related sauropod ''Shunosaurus''; such a tail club was likely not present in ''Spinophorosaurus'', as the hindmost caudal vertebrae became too small. The right supposed osteoderm was somewhat larger than the left and slightly different in shape. This indicates they did not form a pair; in which case they would probably be simply the mirror-inverted counterpart of one another. Rather, these differences indicated two pairs of spines were present originally. In 2013, palaeontologists Emanuel Tschopp and Octávio Mateus reexamined the supposed tail spikes and found they did not have the typical rugose surface of osteoderms seen in other armoured dinosaurs, or the club-like expansion seen in ''Shunosaurus''. Due to their broken edges, They also doubted whether these elements were of different sizes as originally proposed. As these elements were found under the scapula, they instead proposed they represented clavicles, and that the fossils should be reassessed in this regard. Vidal and colleagues concurred with this suggestion in 2015 and 2018.

Classification

The initial

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

presented by Remes and colleagues suggested ''Spinophorosaurus'' fell among the most basal sauropods known, being only slightly more derived than ''

Vulcanodon ''Vulcanodon'' (meaning "volcano tooth") is an extinct genus of sauropod dinosaur from the Early Jurassic of southern Africa. The only known species is ''V. karibaensis''. Discovered in 1969 in Zimbabwe, it was regarded as the earliest-known sau ...

'', ''Cetiosaurus'', and ''Tazoudasaurus''. In this position, it would form the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

, a clade comprising all more derived sauropods. The authors conceded that support for this very basal position was weak, and discussed several alternative placements within eusauropods that would explain anatomical similarities with other sauropods from northern Africa and Laurasia. A similarly basal position outside of Eusauropoda was suggested by several subsequent studies, which placed ''Spinophorosaurus'' as the sister taxon of ''Tazoudasaurus'' or ''

Volkheimeria ''Volkheimeria'' is an extinct genus of sauropod dinosaurs that lived in what is now Argentina during the Early Jurassic, 178–179 million years ago. Its type and only species is ''Volkheimeria chubutensis''. Discovery and naming The only kn ...

''. In a 2013 conference abstract, palaeontologist Pedro Mocho and colleagues re-evaluated the phylogenetic relationships of the genus by incorporating further information from newly prepared bones, arguing that ''Spinophorosaurus'' was nested within eusauropods. According to this analysis, the genus was more derived than ''Shunosaurus'' and ''

Barapasaurus ''Barapasaurus'' ( ) is a genus of basal sauropod dinosaur from Early Jurassic rocks of India. The only species is ''B. tagorei''. ''Barapasaurus'' comes from the lower part of the Kota Formation, that dates back to the Sinemurian and Pliensb ...

'' and close to ''Patagosaurus'' and mamenchisaurids. A much more derived systematic position within Eusauropoda was also proposed by a 2015 study, which found ''Spinophorosaurus'' to be the sister taxon of '' Nebulasaurus''. Spinophorosaurus braincase 3D

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 ...

based on Nair and Salisbury, 2012, which supports a basal position of ''Spinophorosaurus'': Cladogram based on Xing and colleagues, 2015, which supports a more derived position within Eusauropoda:

Evolution

Sauropod distribution and paleoclimatic zones

As one of the most completely known basal sauropods, ''Spinophorosaurus'' has helped to shed light on the early evolution and palaeobiogeography of the group. This has been unclear due to a sparsity of Early and Middle Jurassic remains, particularly outside Asia. Remes and colleagues found that ''Spinophorosaurus'' shares features with Middle Jurassic East Asian sauropods (especially in the neck and tail vertebrae, scapula and humerus) but is very dissimilar from Lower and Middle Jurassic South American and Indian taxa (differences include the shape and development of vertebra features and shape of the scapula and humerus). They suggested this could be explained by the Middle Jurassic sauropod faunas of Laurasia (the northern

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

of the time) and South Gondwana (the southern supercontinent) having been separated by geographic barriers. Earlier it was believed that sauropods were distributed across the supercontinent

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

(which was composed of Laurasia and Gondwana) during the Early and early Middle Jurassic. It had relatively little diversity, until the continent broke up and led to sauropod groups evolving in isolation through

vicariance Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

during the late Middle and Late Jurassic. ''Spinophorosaurus'' shows that features once thought to be derived among East Asian sauropods are rather plesiomorphic (ancestral traits) among eusauropods (eusauropods that colonised Laurasia retained the basal features also seen in ''Spinophorosaurus''). The eusauropods which colonised South Gondwana were a specialised line of the group which had lost said ancestral features during isolation. Remes and colleagues noted that more evidence was needed to support these interpretations but were confident that there was a connection between Jurassic sauropods of North Africa, Europe, and East Asia. As indicated by the anatomy of ''Spinophorosaurus'' and the pattern of Middle Jurassic sauropod distribution, important developments in sauropod evolution may have occurred in North Africa. It was close to the equator and had a summer-wet climate in the Early and Middle Jurassic, with high plant productivity and diversity. On the other hand, the sauropods of South Gondwana were isolated from the equatorial region by the Central Gondwanan Desert in the Early Jurassic, leading to differences in South and North Gondwanan floras. When the desert shrank in the late Middle Jurassic, neosauropods appeared and replaced the sauropod fauna that had been typical of the Middle Jurassic. Since ''Jobaria'' of North Africa is close to the base of Neosauropoda, and because neosauropods such as

diplodocoids 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, ...

were widely distributed in the Upper Jurassic, neosauropods and some of their subgroups may also have originated in the equatorial region of Jurassic Pangaea, which may have acted as a "hot spot" in sauropod evolution. The Jurassic diversification of sauropods was possibly controlled by climatic zones and plant biogeography, rather than just continental differentiation. Vidal and colleagues suggested in 2020 that the wedged sarcral vertebrae and upward deflecected vertebral column of ''Spinophorosaurus'' was an ancestral feature of eusauropods that could also be identified in more derived sauropods. Since eusauropods with short necks and front legs, such as ''

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 ...

'', had wedged sacra, even they would have had upwards deflected vertebral columns in front of the sacrum.

Palaeobiology

''Spinophorosaurus'' and some other sauropodomorphs did not have reduced vestibular apparatuses, a sensory system for balance and orientation in the inner ear, though this might have been expected in a lineage that led to heavy, plant-eating quadrupeds. It is unknown why ''Spinophorosaurus'' retained this feature, but the size and morphology of sauropodomorph labyrinths may be related to neck length and mobility, for example. It is possible expansion of the vestibular apparatus is an indicator of the importance of vision and coordinated eye, head, and neck movements, though interpretation of sauropod vestibular features are still uncertain. At a 2018 conference, Benjamin Jentgen-Ceschino and colleagues reported radial fibrolamellar bone (RFB), a type of bone tissue characterised by radially oriented channels, in the outermost part of the

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

(the outermost bone layer) of the humerus belonging to an adult ''Spinophorosaurus'' specimen and a young adult ''

Isanosaurus ''Isanosaurus'' means "North-eastern thailand lizard" was a sauropod dinosaur from Thailand. It was originally dated to approximately 210 million years ago during the Late Triassic (late Norian to Rhaetian stages), which would make it on ...

''. Normally, the cortex in the long bones of sauropods shows a fibrolamellar complex instead. RFB is considered to be fast growing bone tissue, and has not been reported in sauropods before. Its presence in the outermost cortex is unusual, as it would usually be expected in the innermost cortex (corresponding to juvenile growth). The RFB of the ''Spinophorosaurus'' was buried in the outer cortex, followed by a normal fibrolamellar complex, which indicates the animal survived for some time after its accelerated growth, which probably suggests

pathological Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in th ...

bone growth due to injury.

Motion

Since ''Spinophorosaurus'' is one of the most completely known basal sauropods, it is a good model for biomechanical studies that help to understand sauropod biology and the function of anatomical features. Manipulation of the 3D model by Vidal and colleagues in 2015 showed that each of the frontmost 20 tail vertebrae could deflect up to 20º, and 8–10º in sideways

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

, before limited by the bone morphology. The actual range of movement in a live animal would have been smaller, as the soft tissue as well as the large chevron bones would have been a limiting factor. The first 20 tail vertebrae also became longer towards the end of the tail, as seen in diplodocids, and were powered by enlarged hypaxial musculature, as indicated by the large chevron bones and upwards-angled transverse processes in the first tail vertebrae. Movement in the rear part of the tail was limited as the chevrons were overlapping, as is also the case in

dromaeosaurids Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

and ankylosaurids. Together, these features of the tail may have been part of a specialised function, which is unknown. Joger and colleagues argued in 2009 that the supposed spikes formed a thagomiser at the end of the tail that would have been used for defence against predators. In 2017, John Fronimos and Jeffrey Wilson used ''Spinophorosaurus'' as a model to study how the complexity of neurocentral sutures (the rigid

joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

connecting the neural arch of a vertebra to its centrum) in sauropods may have contributed to the strength of the spine. Sauropods reached their often enormous body sizes by both rapid and extended growth. As long as an individual was growing, the neurocentral sutures were composed of cartilage to permit this growth. Upon reaching full body size, this cartilage would turn into bone, closing the suture. Cartilage, however, is much less resistant to forces that could potentially dislocate the neural arch, such as

bending In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to ...

and

torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Bi ...

; these become especially relevant at large body sizes. Sauropods and other archosauriforms counteract this structural weakness by increasing the complexity of the suture, meaning that the surfaces that connect the neural arch to its centrum had complex ridges and furrows that interlocked. In ''Spinophorosaurus'', suture complexity was most pronounced in the front part of the trunk, indicating that stresses were highest in this region, probably because of the weight of the long neck and rib cage. Complexity became weaker towards the skull and the sacrum. The orientation of the ridges allows for identifying the type of stress that affected the vertebra: In the neck vertebrae, ridges would mainly have prohibited dislocation of the neural arch in a front-to-back direction, while the ridges in the trunk vertebrae were more effective in impeding rotation. In a 2018 conference abstract, Vidal used the virtual ''Spinophorosaurus'' skeleton to test hypothetical mating postures that have been proposed for sauropods that would involve a " cloacal kiss" (as is performed by most birds) rather than a male intromittent organ. Such hypotheses include "leg over back", the male mounting from behind (with the female standing or lying down), as well as "backwards mating". Postures that resulted in dislocation or osteological stops were not considered feasible. The "leg over back" posture was rejected, since it would be impossible for a standing male to reach its leg over the back and hip of a crouching female, even if it was half the size of the male (and it is unknown if sauropods were

sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

in size). The posture wherein the male mounted the female from behind while resting its front legs on the back of the female was possible (the tail was flexible enough to get out of the way), but even if the female was lying down, the cloacae would not approach each other close enough for a "cloacal kiss". The "cloacal kiss" would only be possible through "backwards mating", wherein the male and female approached each other backwards and joined their cloacae with their tails flexed sideways, and movement of the legs would allow individuals of different sizes to mate this way. "Backwards mating" is the only way sauropods could have mated without the need of a male intromittent organ. Such a pose is common in mating arthropods and in the " tied"-phase of mating

carnivoran Carnivora is a monophyletic order of placental mammals consisting of the most recent common ancestor of all cat-like and dog-like animals, and all descendants of that ancestor. Members of this group are formally referred to as carnivorans, ...

mammals such as ''

Canis ''Canis'' is a genus of the Caninae which includes multiple extant species, such as wolves, dogs, coyotes, and golden jackals. Species of this genus are distinguished by their moderate to large size, their massive, well-developed skulls and de ...

''. Vidal and colleagues, in 2020, used 3D models of both the holotype and the juvenile skeleton to estimate the range of motion (flexibility) of the neck. Such estimates assume that the original distance between vertebrae can be reliably predicted, and that the articular processes stay in contact at all times. Vidal and colleagues demonstrated that both assumptions indeed hold true in modern giraffes, increasing confidence in range of motion estimates in extinct animals in general. As ''Spinophorosaurus'' grew, the range of motion of the neck would increase (making steeper neck postures possible); the gap between vertebrae become larger; and the neck become more inclined in neutral posture. Similar changes during growth are also observed in giraffes. The neck would have been as flexible as that of giraffes thanks to the higher number of vertebrae, even though the individual joints were much less flexible than in giraffes. According to this study, ''Spinophorosaurus'' would possibly have been able to feed using the same postures as giraffes, and it could have been the most basal sauropod adapted for high browsing. High browsing is also suggested by anatomical features, including the narrow snout, broad teeth, and proportionally long humerus compared to the scapula. As in the giraffe, both the juvenile and grown ''Spinophorosaurus'' individual would not have been able to reach the ground just by lowering their necks, and possibly splayed their forelimbs for drinking. While sleeping, giraffes bend their necks sideways against the body. Although the vertebral articulations would have been flexible enough for such bending in ''Spinophorosaurus'', it might have been prohibited by the elongated cervical ribs. Also in 2020, Vidal and colleagues added that the more vertical posture and greater upwards and downwards motion revealed by the digital model also supported high browsing abilities in ''Spinophorosaurus''. High-browing therefore appears to be a basal feature within Eusauropoda, and the body proportions of non-sauropod sauropodomorphs indicate they were medium height browsers.

Palaeoenvironment

''Spinophorosaurus'' is known from the Irhazer Shale of Niger, which has been determined to represent the base of the Irhazer Group (based on the presence of

red clay Ultisols, commonly known as red clay soils, are one of twelve soil orders in the United States Department of Agriculture soil taxonomy. The word "Ultisol" is derived from "ultimate", because Ultisols were seen as the ultimate product of continu ...

that show

interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedim ...

sand beds with traces of subaerial exposure and dinosaur footprints), which is stratigraphically below the outcrops of the Tegama Group. The Irhazer Group was earlier considered Jurassic to earliest Cretaceous in age, as the overlying Tiourarén Formation was once considered to be of Lower Cretaceous age. Subsequent studies have found the latter formation to be Middle Jurassic to early Late Jurassic. The stratigraphical and phylogenetic position of ''Spinophorosaurus'' (compared with other basal sauropods from around the world) indicates it could be Middle Jurassic (

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stra ...

–

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Str ...

) in age. Since the strata of the Irhazer Group cannot yet be directly dated, it might be as old as Lower Jurassic. The lower limit is defined by the underlying Agadez Group, which is

Upper Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

in age (based on the presence of ''

Chirotherium ''Chirotherium'', also known as ''Cheirotherium'' (‘hand-beast’), is a Triassic trace fossil consisting of five-fingered (pentadactyle) footprints and whole tracks. These look, by coincidence, remarkably like the hands of apes and bears, with ...

trace fossils A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils ...

). The ''Spinophorosaurus'' skeletons were discovered in a massive to finely laminated red siltstone, whose matrix contained some carbonate. The fossils were recovered from the upper half of this several metres-thick siltstone layer. The layers there are subhorizontal, bearing minor faults, and commonly contain palaeosoils and carbonate at the top of the unity (about a metre above the level with the skeletons). Sediments of the Irhazer Group were deposited under conditions that were fluvio-

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

(associated with rivers and lakes), during a time when the Iullemmeden Basin was part of a great river-valley system, which was connected with the Proto-Atlantic coast of Gondwana through adjacent basins. Four theropod teeth were found closely associated with the ''Spinophorosaurus'' holotype (by a vertebra, pubis, and in the acetabulum); three had similarities with

Megalosauridae Megalosauridae is a monophyletic family of carnivorous theropod dinosaurs within the group Megalosauroidea. Appearing in the Middle Jurassic, megalosaurids were among the first major radiation of large theropod dinosaurs. They were a relatively ...

and

Allosauridae Allosauridae is a family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in ...

, while the fourth belongs to what may be one of the earliest known members of

Spinosauridae The Spinosauridae (or spinosaurids) are a clade or family of tetanuran theropod dinosaurs comprising ten to seventeen known genera. They came into prominence during the Cretaceous period. Spinosaurid fossils have been recovered worldwide, in ...

. The fact that the teeth are poorly preserved while the ''Spinophorosaurus'' skeleton is well-preserved indicates that the teeth were transported before being buried with the sauropod. Dinosaur tracks were found some hundred metres away from the ''Spinophorosaurus'' site, including a trackway of six footprints from a mid-sized sauropod as well as 120 well-preserved didactyl (two-toed) theropod footprints. The didactyl tracks were originally thought to have been left by paravian theropods (such as dromaeosaurs or

troodontids Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...

, which have two weight-bearing toes), but were subsequently interpreted as having been produced by swimming theropods (explaining why one toe did not leave a trace).

References

External links

The Dino Project
– Google Arts & Culture photo series about the Braunschweig Museum excavations in Niger {{featured article Fossil taxa described in 2009 Fossils of Niger Mesozoic Niger Middle Jurassic dinosaurs of Africa Gravisauria