Spinophorosaurus
Spinophorosaurus
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Spinophorosaurus

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Spinophorosaurus

Spinophorosaurus is a genus of sauropod dinosaur that lived in what is now Niger during the Middle 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, 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 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, 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 13 m (43 ft) in length, whereas the paratype was about 14 m (46 ft) long. The shoulder height reached by these individuals was estimated at around 4 m (13 ft), and the weight at about 7 metric tons (7.7 short tons). The braincase was short, deep, and broad, and the neuroanatomy was in some ways intermediate between that of basal sauropodomorphs 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 vertebrae. 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 clavicles.

Spinophorosaurus has been classified as either a very basal sauropod, or inside Eusauropoda, a more derived group. The anatomy, age, and location of specimens indicate that important developments in sauropod evolution may have occurred in North Africa, possibly controlled by climatic zones and plant biogeography. Features of the vestibular apparatus 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 thought to be Middle Jurassic in age. It was formed by deposits from rivers and lakes in a great river-valley system.

The rich dinosaur fauna of Niger was brought to scientific attention through French and Italian excavations in the 1960s and 1970s. This led to the description of new genera from Lower Cretaceous rocks, most prominently the iguanodontian Ouranosaurus. An older succession of rocks, the Tiourarén Formation, was explored by American palaeontologist Paul Sereno, 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 Afrovenator from the Tiourarén; most finds were discovered along a cliff known as the Falaise de Tiguidit in the southern Agadez Region. 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 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 30 km (19 mi) north of the Falaise de Tiguidit and near the town of Aderbissinat in the Agadez Region, and part of the Irhazer Shale (or Argiles de l'Irhazer), a geological formation 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 (thigh bone) of what would later become the holotype specimen of Spinophorosaurus. An associated scapula (shoulder blade) and a vertebra were discovered soon after. The sediment in the locality, a hard but brittle siltstone, could be removed from the bones using light hammer blows.

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 1 March 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 16 March; the trucks arrived on 20 March. Although disappointed, the German team discovered a second Spinophorosaurus specimen, the future paratype, 15 m (49 ft) apart from the first, on 17 March. 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 19 March. On 20 March, 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 25 March, 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.

By 27 March, 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. Excavation was completed on 2 April, and the fossils were packed for transport to the port of Cotonou on 3 April. 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. 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).

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