When it comes to dinosaurs, they are classified into different categories according to their features. Nigersaurus is a dinosaur from the superfamily Diplodocoidea under the subfamily Nigersaurinae that lived 115 to 105 million years ago throughout the middle cretaceous period. It was found in the Republic of Niger in the Gadoufaoua area in the Erlhaz Formation. Fossils of this dinosaur were first described in 1976. After the further discovery of more complete remains, it was given the name Nigersaurus taqueti in 1999. The genus name means ‘Niger reptile’ in which is a reference to the country of its discovery. The specific name pays tribute to palaeontologist Philippe taqueti who organized the palaeontological expeditions to Niger which led to the discovery of the first fossils.
History of discovery
It is among the most common vertebrates in the formation found. The expeditions to Niger which led to the discovery of its fossils was led by a French palaeontologist Philippe Taquet. The remains were discovered in that expedition during 1965-1972 and were first mentioned in 1976 in a published paper. Not until further discoveries, this dinosaur which is also a common genus was poorly known. This was a result of poor preservations and maintenance of its remains. The discoveries of more fossils were led during expeditions in 1997 by Paul Sereno, the American palaeontologist. Poor preservation of the remains arose from the delicate skull and skeleton and their highly pneumatic constructions resulting in disarticulation of the fossils. The skull fossils being the most delicate, some were so thin that through them a strong beam of light was visible.
Sereno and colleagues named and described it in more detail only in 1999 according to the remains found by new individuals. Furthermore, another sauropod Jobaria from Niger was named from the same article. The specific name taqueti appreciates Taqueti for his work as he was the first palaeontologist to organize that large-scale expedition to Niger. A partial neck and skull comprised the holotype specimen (MNN GAD512). A scapula and limb material found nearby were also of the same specimen. The fossils are housed at the Niger’s National Museum.
History of description
It was first discovered in the 1965-72 expedition which happened in the Republic of Niger. The fossils of this dinosaur were first described in 1976. With further discoveries of this dinosaur, Paul Sereno and colleagues named and described more details of this dinosaur in 1999. Sereno and Jeffrey A. Wilson, the American palaeontologist provided the first detailed description of the feeding adaptations and skull in 2005. Furthermore, based on the specimen that was discovered ten years earlier, its skeleton’s more detailed description was published by Sereno and colleagues in 2007. A plastic model of the neck and head, a reconstructed skeleton mount along with the original fossils were at the National Geographic Society in London. It was nicknamed a ‘Mezoic cow’ in the press. Sereno emphasized its uniqueness as the most uncommon dinosaur he had spotted ever. He compared its appearance to a vacuum cleaner and Darth Vader, its tooth shear to sharpened piano keys and conveyer belt.
Its numerous specimen collected by American and French expeditions remain to be described. Similar teeth to those of Nigersaurus have been identified in Brazil on the Isle of Wight. Though it is unknown if they belong to the relatives of this whose fossils have been found in the area. Besides, a lower jaw to the titanosaurs Antarctosaurus may have evolved convergently it is similar to that of this dinosaur.
Taquet initially described its remains in 1976 to belong to dicraeosaurid. Though in 1999, Sereno’s team reclassified it as rebbachisaurid diplodocoid. This was due to the analysis that small size and short necks were familiar among basal diplodocoids. Rebbachisauridae is within the superfamily Diplocoidea and is the basalmost family consisting of the short-necked dicraeosaurids and long-necked diplodocids. It shared its eponymous subfamily Nigersaurinae with the other two, Demandasaurus which was closely connected to it but from Spain. It was identified and described by Fidel Torcida Fernández-Baldor, the Spanish palaeontologist and colleagues in 2011. Tataouinea from Tunisia was described by Federico Fanti, the Italian palaeontologist and colleagues in 2013.
Like all sauropods, it was a quadruped. It had thick hind legs, a small head and a prominent tail. Although for a sauropod, it was considered small as it was about 9 m (30 ft) long due to its short neck. Its femur reached only 1 m (3 ft 3 in). For its short neck, there’s no big difference compared to the rest as nearly all rebbachisaurids had short necks and a body length of 10 m (33 ft) or less. The neck consisted of thirteen cervical vertebrae. Its body size may have weighed around 4 t (4.4 short tons) compared to a present-day elephant. Rebbachisaurus was the only member of the family with a larger size of sauropods.
With all its remarkable discoveries, the skull was the most delicate with four openings and compared to other sauropodomorphs its skull was larger. A total area of 1.0 cm2 (0.16 sq in) is the bone that connected the muzzle to the backside of the skull and is usually less than 2 mm (0.08 in) thick. Conversely, the skull resisted supporting teeth shearing and this made it unique among the sauropodomorphs, which was its closed upper temporal fenestra. Other features of the skull are the bony nostrils and nasal openings which were elongated. The front margin of its bony nostril was known to emerge closer to the snout compared to the rest of the diplodocoids. The snout was considered proportionately shorter with its snout tip not protruding and the tooth row which was not all prognathous. It was distinct due to its elongated frontal bone which formed much of the skull-proof and a marked cerebral fossa.
Its teeth are placed afar to the front and no other tetrapod has this feature. The upper and the lower tooth row are transversely rotated which adds more to its uniqueness. Furthermore, when you’re wondering what dinosaur has 500 teeth, it had that description. It had an extreme enormous mouth lined with teeth which were one of its adaptations for browsing plants close to the ground. The teeth in the upper jaw may have been 20-30% bigger compared to those of the lower jaw while the few unknown are of uncertain maturity. The slender teeth were oval in cross-section due to the slightly curved crowns. Besides all these, they are identical. It had more than 500 teeth that were replaceable. There was a column of nine teeth replaceable within the jaw under each active tooth. With an overall of more than 500 teeth active and replaceable, the lower jaw comprised of 60 columns while the upper jaw had 68 columns which are so-called dental batteries. The dental batteries erupt in unison and not each column individually. Its enamel was thicker ten times on the outwards compared to on the inner side. Moreover, they were highly unbalanced which was a condition only known in advanced ornithischians.
All in all, it is the only tetrapod animal that had teeth extended laterally past the front hence had jaws wider compared to the skull.
Having done microtomography on its skull elements, Sereno and his team created a ‘prototype’ to examine the skull. They examined the semicircular canals of its ear and constructed an endocast of the brain in which they found it to be aligned horizontally. In 2007 their study alleged that cervical vertebrae and the occiput’s structure controlled the downward and upward movement of the neck and rotation of the skull. This biomechanical analysis summarized that the muzzle and head be habitually oriented 67° downwards hence adapting to ground-level browsing. This was unlike the rest of sauropods with their heads held in a more horizontal position.
It can feed with the head and neck posture turned downwards as agreed by Mike P. Taylor, the British palaeontologist and his team in their 2009 study. It was also supported by the 2007 study though challenged it was its regular posture. However, compared to the modern species, Sereno’s team methods were imprecise as they were not reliable in determining the head posture it held its head like other sauropods. This is supported by the study that modern animals’ heads and neck posture do not automatically fit their regular head posture.
Further study of modern mammals was done in 2020, by French palaeontology Julien Benoit and colleagues about the correlation between semicircular canals to head posture. It was summarized that using semicircular canals as a proxy may lead to the imprecise orientation of the skulls. It was found that semicircular canals related more to the diet and both semicircular canals and the head posture strongly correlated with phylogeny.
Its dorsal vertebrae linked pneumatic spaces at the bottom of the neural spines hence contributing to its distinction. The presacral vertebrae were pneumatized heavily to whereby the column involved a series of hollow ‘shells’ each in the middle separated by a thin septum. The thin bone plates’ centra were filled with air spaces due to little to no cancellous bone. It also had vertebral arches which were heavily pierced by extension of external air sacs having their side walls minimized but 2 mm (0.08 in) thick intersecting laminae, the ridges joining pneumatic openings. The tail’s vertebrae had solid centra. Pectoral girdle bones and pelvic were thin usually thick by only several millimetres. It also had a distinguishing feature, an important rugosity on the median line aspect of the scapular blade.
Like other sauropods, it had robust limbs, its front legs consisted of two-thirds back legs’ length like in most diplodocoids. Though its limbs were not as specialized as other parts of the skeleton.
Diet and feeding
As suggested by Sereno’s team, it was a non-selective browser on the ground level. The sauropod gathered enough food and crop it close to the ground due to its lateral tooth row and the width of the muzzle. The facets of the externally facing side of the upper teeth furtherly support this hence wore the animal’s teeth as it fed. Its jaw movement was restricted to precise up and downs motion as it bears signs of low-angle tooth-to-tooth wear on the inside of the maxillary crowns. Worn teeth from the lower jaw are expected to show contrasting tooth-to-tooth wear despite not being discovered yet. Its short neck limited its browsing range compared to diplodocids. Moreover, raising its head well above the ground doesn’t guarantee that it will browse on the item there.
It is one of the sauropods estimated to have the weakest bites. This comes about due to the adductor muscle and other mastication muscles weakness. This is a result of the adductor muscle of the jaw appears to have attached to the quadrate instead of the supertemporal fenestra. Furthermore, Whitlock and colleagues in 2011 indicate that it ate quite soft herbs or plants like low-growing ferns. This is due to the small and parallel nature of the tooth scratches and pits. Therefore, due to its lateral orientation of teeth, it would have been unable to chew. Its tooth crowns wore down faster compared to any other dinosaurian herbivores. Besides, its tooth replacement rate was the highest of any known dinosaur. In every 14 days, each tooth once in which the rate was previously estimated lower. Sauropods thought to have been canopy browsers had broad tooth crowns and lower tooth replacement rates compared to this dinosaur.
Its potential foods were the making of ferns, angiosperms and horsetails as grass evolved late Cretaceous. Due to its short neck, stiff structure and lack of appropriate habitat, it was unlikely to feed on cycads, conifers and aquatic vegetation. Also, its evenly placed teeth as suggested by Wedel would have functioned well like a comb by straining water invertebrates and water plants like flamingos. All in all, according to its adaptations, it is suited to eat other low-growing plants and short conifers by low-browsing.
When it comes to features of this dinosaur, it has distinguishing features and others are likely to be similar to other sauropods. Similarities may be more due to the common features of all sauropods especially with members of the same subfamily. These features are as mentioned above, teeth, necks, size and weight. Besides, some of the features distinguish it from other dinosaurs hence making it unique. Also when you’re wondering what dinosaur has 500 teeth, this is the most distinguishing feature of this dinosaur. All in all, provided with all this information, what is there to miss on this dinosaur.