What dinosaur has 500 teeth? Inside the conveyer belt jaw of Nigersaurus

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What dinosaur has 500 teeth and replaced each and every one of them every 14 days? With 15 times more teeth than the human set of 32, Nigersaurus taqueti hacked through low-lying vegetation with choppers like a lawn mower, paleontologist and National Geographic Explorer Paul Sereno told National Geographic just years after he and colleagues first described and named the dinosaur.
About as heavy as an adult African forest elephant, this dinosaur would have weighed about two tons and stretched about 30 feet long from nose to the tip of its tail. The herbivore wandered lowlands of western Africa about 105 million years ago in what's now the Republic of Niger.
Nigersaurus was one of the most effective plant-eating creatures to have ever evolved. Here's what you need to know about Nigersaurus and its toothy way of life.
The bones of Nigersaurus first came to the attention of paleontologists in the middle of the 20th century. Between 1965 and 1972, French paleontologist Philippe Taquet used previous fossil reports to confirm the suspected bonebeds in Niger. His search turned up multiple prehistoric species new to science, such as the sail-backed, duckbilled dinosaur Ouranosaurus and the gharial-like crocodile Sarcosuchus.
One site, Gadofaoua, was especially promising and brimming with the bones of large dinosaurs. Taquet did not describe them in detail or name them, as there were so many other fossils in the area to study. The bones would wait 30 years for another team of paleontologists to dig in further.
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In 1997, a field team organized by Sereno, who is also a National Geographic Explorer, rediscovered the bones at Gadofaoua. 'The locality is quite remote, and the temperatures and shifting sands mean that it can be a challenging place to work,' says University of Michigan paleontologist Jeff Wilson Mantilla, who helped name Nigersaurus.
Each piece of bone was extremely delicate. Some were so thin, light could shine through them. But after careful excavation, preparation, and study, it was clear that Taquet's sauropod was a new dinosaur unlike any seen before.
In 1999, Sereno, Wilson Mantilla, and colleagues presented a scientific description of the plant-eater and named it Nigersaurus taqueti in honor of its country of origin and Taquet. Further finds made the following year filled even more of the skeleton, which showed that Nigersaurus was a very unusual relative of dinosaurs like Diplodocus.
Experts found multiple Nigersaurus bones at the site, including neck bones still connected to each other and a jumble of several skull bones.'The skull bones were so strange looking that it was challenging to identify which element we were looking at,' Wilson Mantilla says.
Paleontologists have continued studying Nigersaurus and how the dinosaur lived. Its eyes were positioned high on its skull, which may have given the herbivore overlapping visual fields to better watch out for stalking carnivores. A study of the dinosaur's limb bones further indicated that Nigersaurus had thin walls compared to the limb bones of large mammals.
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Air sacs that invaded and surrounded some of the bones of Nigersaurus, like those found in birds that make their bones hollow, helped keep the dinosaur light enough that the animal did not need bulky bones to support its weight like large mammals do. Having hollow bones supported by air sacs was one of the key traits that allowed dinosaurs like Nigersaurus to get big.
While all dinosaurs replace their teeth throughout their lives, Nigersaurus' process was unique. As dino teeth form, they are marked with tiny lines that form each day.
'Counting those lines tells you how old the teeth are,' Wilson Mantilla says. The count on Nigersaurusindicated that each of its teeth was replaced every two weeks, he notes, with seven replacements forming behind the exposed tooth at any one time.
The shape of the dinosaur's jaws offered a clue to its dental overachieving. The muzzle of Nigersaurus was square, like a vacuum. Square muzzle shapes are common among animals that graze low to the ground, a hint that Nigersaurus did so too.
"Its mouth appears designed for nipping rather than chomping or chewing," Sereno said in a 2007 interview with National Geographic. Wear patterns suggest Nigersaurus' teeth slid by one another like a pair of shears.
Such low-growing plants are often tough to eat. Plants like horsetails contain tough, crystal-like material called silica, and vegetation that grew low to the ground would also have a lot of sand or other grit in it Wilson Mantilla says. Feeding on such roughage would have worn down the dinosaur's teeth very quickly, and so Nigersaurus evolved to replace its teeth fast.
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Experts still have a lot to learn about Nigersaurus and how it evolved to be different from other plant-eating dinosaurs. Studying the unusual herbivore might help experts better understand how such dinosaurs spread all over the planet and thrived for so many millions of years. In time, bones that started as mysteries in the desert may unlock new paleo puzzles.
Paleontologists uncovered the bones of many individual Nigersaurus from Gadofaoua, but no single complete skeleton. Thanks to cutting-edge technology, however, Wilson Mantilla and colleagues were able to make digital scans of the collected Nigersaurus bones in 2007 and adjust them to the same scale to create a reconstruction of the dinosaur. It was one of the first times paleontologists had used CT scans to reconstruct the skull anatomy of a dinosaur.
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The CT scans also revealed the anatomy and position of the dinosaur's inner ear, which shows us how animals hold their heads and balance their bodies. For Nigersaurus, the digital scan indicated that the herbivore kept its muzzle tilted down toward the ground. Researchers also found that the brain cavity of Nigersaurus showed relatively small parts of the brain relating to smell.
From this discovery, researchers can assume Nigersaurus probably wasn't very good at sniffing out approaching carnivores or where the tastiest plants might be. But that doesn't seem to have been a problem for a dinosaur that grazed all day.