Nigersaurus: The 'Mesozoic Cow' With More Than 500 Teeth

Calling something "elephant-sized" usually means it's quite big, if not downright enormous.

Nigersaurus was a little over 29 feet (or around 9 meters) long. By the most liberal estimates, it weighed roughly 4.4 tons (i.e., 4 metric tons). So overall, the dinosaur was about the size of a modern African elephant.

There's just one caveat. You see, Nigersaurus was a sauropod. One of the major dinosaurian groups, the plant-eating, small-headed sauropods hung around for about 140 million years. Their ranks included the largest animals to ever walk the Earth.

Experts say the biggest species may have been over 110 feet (33.5 meters) long. Meanwhile, 40- to 85-foot (12- to 26-meter) sauropods are common throughout some parts of the fossil record.

In comparison, Nigersaurus was on the small side. What caught everyone's attention was the dinosaur's mug.

Sereno's vacuum comparison is right on the money. Viewed from above, Nigersaurus' wide muzzle looks like the business end of one of these household appliances.

Those jaws held something never before seen in a sauropod dinosaur: It was one of the first dinosaur skulls with tooth, or "dental," batteries.

We're not talking about AA Duracells here. Dental batteries were efficient food processing tools used by many plant-eating dinos. They consisted of vertically stacked columns of replaceable teeth. Whenever the top tooth wore out in any given column, the one right below it would move upwards and take the old tooth's spot.

Better yet, those tooth columns were packed right alongside each other—like canned sardines. So a dinosaur armed with dental batteries could comfortably house several hundred teeth (old and new) inside its mouth.

In Nigersaurus' case, the upper jaws contained 60 columns of small, needle-shaped upper teeth. And no fewer than 68 very sharp teeth were present on the lower jaws. Tallied together, upper jaw and lower jaw, the beast had more than 500 individual teeth.

Dinosaur-hunters are used to finding dental batteries in beaked herbivores like the horned Triceratops and shovel-billed Edmontosaurus. But they're rare among the sauropods.

Tooth orientation is just as important as tooth quantity. Ask anyone who's ever needed braces.

All the tooth columns in Nigersaurus' dental batteries were lined up, unlike the teeth of other dinosaurs, at the very front of its mouth, positioned along the muzzle's gently curved outer edge.

What's a dinosaur to do with chompers like this animal's teeth? Nibbling on treetops probably wasn't an option. Nigersaurus wasn't just small-bodied for a sauropod, it also had a fairly short neck.

No, the evidence suggests Nigersaurus fed at ground level. Sort of like a cow.

Nigersaurus was named after the West African country where its fossils have been found: The Republic of Niger. Back when this animal roamed, forests and braided rivers covered the landscape. (Nigersaurus would've had to watch out for Sarcosuchus, a huge relative of modern crocodiles.)

That wide muzzle with its Nigersaurus teeth was perfect for scooping up ferns, horsetails and other low-lying plants. And with the bountiful teeth, the dinosaur would've had no trouble shearing through this vegetation.

Eating like that can be rough on your dental health unless you have a syteady supply of replacement teeth. Nigersaurus must have worn out its tooth crowns at a rapid-fire pace. Good thing it had a constant supply of fresh replacement teeth. According to a 2013 study published in the journal PLOS One, Nigersaurus likely replaced each "new" tooth after just 14 days.

Because Nigersaurus ate with its head down, experts have wondered about its posture. Sereno and his co-authors once argued that the herbivore aimed its face and neck downwards — whether it was feeding or not — as a matter of habit.

Through a painstaking process, this team was able to reconstruct the inside of Nigersaurus' skull. That gave them a good look at the lateral semicircular canal (LSC) of the inner ear, which helps animals keep their balance.

Judging by the LSC orientation in Nigersaurus, Sereno and company hypothesized that the animal usually walked around with its snout pointed to the ground at a 67-degree angle. Picture a moping teenager and you'll get the idea.

Other researchers have disputed this claim, though. Studies released in 2009 and 2013 found that the position of the LSC can't reliably tell us what any given sauropod's normal head posture looked like. Someone needs to build a time machine already.

Nigersaurus stayed under the radar for quite a while. The first known fossils belonging to this animal were recovered during the 1950s by French paleontologists in the Nigerian Sahara. Unfortunately, most of these bones were isolated or fragmentary.

Scientists working at the time didn't even bother to give the sauropod a name.

Things got more interesting in 1997. That's when a member of Sereno's field team noticed some Nigersaurus skull bones. Over the course of two expeditions, enough material was found to reconstruct about 80 percent of the beast's skeleton.

And what a skeleton it was! The newfound fossils gave us our first look at the dino's complicated dental batteries and vacuum cleaner mouth. Sereno named the species Nigersaurus taqueti — as an homage to French paleontologist Philippe Taquet — in 1999.

Scientists probably would've found more Nigersaurus remains a whole lot sooner if it hadn't been for this animal's fragile bone structure. To quote a 2007 Sereno-led study, this critter had a "featherweight skull." Several bones in Nigersaurus' head were under 0.08 inches (or 2 millimeters) thick.

The oddities didn't stop there.

Like today's birds, many prehistoric dinosaurs had hollow bones containing air sacs. Nigersaurus vertebrae took this to an extreme. Measured by volume, some of its backbones actually contained more air than ... well, than bone.

Wafer-thin fossils with thin bone plates aren't the easiest things to preserve and study. But dag nabit, someone's gotta do it!

Originally Published: Dec 31, 2020