Spinophorosaurus

Spinophorosaurus Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Naturkundemuseum Braunschweig ; the fossils on the floor are authentic
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Clade:	†Gravisauria
Genus:	†Spinophorosaurus Remes et al., 2009
Species:	†S. nigerensis
Binomial name
†Spinophorosaurus nigerensis Remes et al., 2009

Spinophorosaurus is a

The subadult holotype specimen is estimated to have been around 13 m (43 ft) in length, whereas the

The rich dinosaur fauna of

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 1 km (0.6 mi) 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.^{[2]: 17–27, 38 [1][5][6]} It was the first German dinosaur expedition to Africa in almost a century.^{[1]: 29 [7]}

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 paratype, 15 m (49 ft) 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 200 L (53 US gal) 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 43–45 °C (109–113 °F). On March 25, all but two of the German team members were ill, suffering diarrhoea and circulation problems. Throughout the excavation, progress was documented with photographs and field notes.^{[2]: 29–45 [8]}

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 60–80 cm (24–31 in) of sediment to make sure that all fossils had been collected.^[2]: 60 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 80 km (50 mi) 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.^{[2]: 68–73 [9]} 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).^{[2]: 100, 107}

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 as well as by a smaller, newly built local museum.^[2]: 143 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.^{[2]: 79–85 [10][11]} 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);^[12] a caudal vertebra was put on display at the Elche museum in 2018.^[13] 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.^[14]

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

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, changes during growth).^[20][15]

Description

The holotype specimen was initially estimated to have been around 13 metres (43 ft) in length when measured along the vertebral column, while the paratype was about 13 per cent larger, measuring around 14 m (46 ft). 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.^[1][2] A later 3D photogrammetry model of the holotype skeleton measures 11.7 m (38 ft) from head to tail, the proportions differing from estimates based on 2D skeletal reconstructions.^[12] In 2023, Vidal listed the holotype as 11 metres (36 ft) long, the paratype as 13 metres (43 ft), and the juvenile as 3 metres (9.8 ft).^[21] The shoulder height reached by these individuals was estimated at around 4 m (13 ft),^[2] and the weight at about 7 metric tons (7.7 short tons).^[1][22]

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 prezygapophyseal facets on the neck vertebrae and a specialised first back vertebra. Consequently, the snout of Spinophorosaurus would have been held about 5 metres (16 ft) 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 2.15 metres (7.1 ft).^[23]

Skull

The frontal bones of the

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.^[25] The neck was composed of 13 cervical vertebrae. The trunk had 12 dorsal and four sacral vertebrae. The tail comprised more than 37 caudal vertebrae.^[1] Complex elements, individual vertebrae are composed of a lower part, the centrum, and an upper part, the neural arch. Important landmarks of the neural arch include the upwards projecting neural spine (spinous process) and the sideward projecting diapophyses, which together give the vertebra a T-shape in front and rear views. Pairs of articular processes connecting with neighboring vertebrae are protruding from the front (prezygapophyses) and rear (postzygapophyses).^[26]

The cervical vertebrae were similar to those of Jobaria and Cetiosaurus. 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 pleurocoels 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 epipophyses, 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 (unique feature) of Spinophorosaurus.^[1]

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

evolved independently from the former group.^[27] 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 and Patagosaurus, in contrast, the rearwards dorsals were more elongated and had pronounced pleurocoels. The neural canal of the dorsal vertebrae was very narrow but high.^[1] Hyposphene-hypantrum articulations (accessory articular processes) were present in all dorsals, making the spine more rigid.^[1][28] 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. 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.^[1]

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. 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 chevrons (paired 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.^[1]

Girdles, limbs, and misidentified tail spikes

osteoderms

(A–C), girdle, and limb elements

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.^[19] In these respects it was similar to mamenchisaurids from Asia but different from the genera Vulcanodon, Barapasaurus, and Patagosaurus from Gondwana (the southern supercontinent of the time), in which the upper end was only weakly broadened, and the rear flange lacking. The coracoid, 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 lesser trochanter on its upper end—a bony projection serving as attachment site for muscles that drew the hind leg forwards and inwards. The fourth trochanter, 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 astragalus had facets for articulation with the tibia and fibula that were not separated by a bony wall, and as many as eight nutrient foramina (openings that allow blood vessels to enter the bone).^[1]

Skeletal reconstruction from the original 2009 description (above) showing tail spikes that may represent clavicles, as well as a too horizontal posture, and outdated life restoration (below) showing those same features

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.^[1]

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.

PhD thesis.^[29][19][30]

Classification

The initial

sister taxon of Eusauropoda, 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 (the northern supercontinent).^[1] A similarly basal position outside of Eusauropoda was suggested by several subsequent studies,^[31][32][33] which placed Spinophorosaurus as the sister taxon of Tazoudasaurus^[31] or Volkheimeria.^[32] 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 and close to Patagosaurus and mamenchisaurids.^[27] 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.^[34]

neosauropods

.

Cladogram based on Nair and Salisbury, 2012, which supports a basal position of Spinophorosaurus:[31] Gravisauria Vulcanodon Tazoudasaurus Spinophorosaurus Barapasaurus Rhoetosaurus Eusauropoda Shunosaurus Patagosaurus Omeisaurus Mamenchisaurus Turiasauria Losillasaurus Neosauropoda

Cladogram based on Xing and colleagues, 2015, which supports a more derived position within Eusauropoda:[34] Sauropoda Vulcanodon Eusauropoda Shunosaurus Mamenchisauridae Barapasaurus Nebulasaurus Spinophorosaurus Patagosaurus Turiasauria Haplocanthosaurus Neosauropoda

A 2022 study by palaeontologist Xin-Xin Ren and colleagues found Spinophorosaurus to be the basalmost mamenchisaurid, sharing eight derived feaures with this group. These researchers also found other non-Asian taxa (Rhoetosaurus from Australia and Wamweracaudia from Africa) to be mamenchisaurids, and concluded that the group was more widespread than previously thought. While they could not determine where the group originated, they stated it must have been widespread across Asia and Africa during the late Early to Middle Jurassic, before Laurasia and Gondwana disconnected during the late Middle to Late Jurassic.^[35]

Evolution

type locality

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 and South Gondwana having been separated by geographic barriers. Earlier it was believed that sauropods were distributed across the supercontinent Pangaea (which was composed of Laurasia and Gondwana) during the Early and early Middle Jurassic.^[1]

Pangaea had relatively little diversity, until the

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.^[1]

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

climatic zones and plant biogeography, rather than just continental differentiation.^[1] 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, had wedged sacra, even they would have had upwards deflected vertebral columns in front of the sacrum.^[23]

Palaeobiology

crown

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.^[24]

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

pathological bone growth due to injury.^[36]

Motion

3D models showing possible up-down and sideways neck posture flexion in a subadult (A-B left, A-G right) and juvenile (C-D left, B-H right) Spinophorosaurus

Since Spinophorosaurus is one of the most completely known basal sauropods, it is a good model for

thagomiser at the end of the tail that would have been used for defence against predators.^[2]

In 2017, John Fronimos and Jeffrey Wilson used Spinophorosaurus as a model to study how the complexity of neurocentral sutures (the rigid

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.^[37]

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 "

carnivoran mammals such as Canis.^[38]

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.^[15]

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.^[15] 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.^[23]

Palaeoenvironment

theropod

tracks found near the Spinophorosaurus specimens (left), and four theropod teeth found with the holotype (right)

Spinophorosaurus is known from the Irhazer Shale of Niger, which has been determined to represent the base of the

trace fossils).^[1][39]

The Spinophorosaurus skeletons were discovered in a massive to finely laminated red siltstone, whose

Proto-Atlantic coast of Gondwana through adjacent basins.^[39][40]

Four theropod teeth were found closely associated with the Spinophorosaurus holotype (by a vertebra, pubis, and in the acetabulum); three had similarities with

troodontids, 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).^[39][42]

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    PMID 21339816
    .
40. ISBN 978-0444825711
    .
41. S2CID 53331040
    .
42. ISBN 978-0-253-02102-1
    .

External links

Wikimedia Commons has media related to Spinophorosaurus.

• The Dino Project – Google Arts & Culture photo series about the Braunschweig Museum excavations in Niger

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