In the new study, Sereno's team generated 3-D images of the dinosaur's braincase using CT scans.
The scans revealed that Nigersaurus's teeth were replaced faster than those of any other dinosaur, with some ten replacements stacked up behind each one, Sereno said. "We looked into its ear regions to try to work out which way the skull was orientated in life," Sereno added.
The team's findings suggest the dinosaur's head faced downward, at a right angle to the neck.
"That made a lot of sense given the shape of the muzzle—it was mowing down plants along the ground," Sereno said.
Nigersaurus likely ate soft plants such as young ferns and horsetails, probably lifting its neck to a horizontal level but not much higher, he said.
The dinosaur's head posture and unusual wear on its teeth paints a different behavioral picture for Diplodocus and related sauropods. Until recently, scientists believed the animals craned their necks up to trees for their meals.
"[Diplodocus] has also got the downturned head and square jaws," Sereno said. "It's like a less extreme version of Nigersaurus. I think it also was a ground feeder."
Paul Upchurch, a paleobiologist at University College London in the United Kingdom, commented that the new study reinforces more recent thinking that so-called diplodocoid sauropods were predominately low-level browsers.
"Nigersaurus having its head pointing towards the ground fits very nicely with how the jaws were working and what the teeth were doing," he said.
A Walking Chandelier
"Elements of the same [feeding] system were obviously shared with other diplodocoids, but they may not have been as extreme as this," Upchurch added.
The skull of Diplodocus, for instance, probably wasn't designed to point towards the ground at such a steep angle, he said.
"Diplodocus also had a much longer neck so maybe it was able to feed not just near the ground but over a wider variety of levels," he added. Nigersaurus is a "fascinating animal" that's "weird" even in respect to its close relatives, Upchurch said.
"Looking at its skull, you would think just the slightest little bite and the whole thing would shatter," he added.
"Obviously it had a way of coping with the bite forces involved."
Sereno, the study leader, noted that whereas elephants use massive teeth positioned at the back of massive jaws for eating, "Nigersaurus puts its teeth in the worst position—way up front, away from the joint." The backbone of the dinosaur was likewise pushed to an extreme, Sereno added.
"The vertebrae look more like eggshells," he said. "They are more air than bone." (Related news: "Newly Discovered Dinosaur Had Giant Neck, Air-Filled Bones" [March 21, 2006].)
Having such a dainty skull and backbone would have made the dinosaur much lighter, Sereno added, "but it really does look like a walking chandelier."
"How did this dinosaur do it?" he asked.
It's a question, he said, that requires further study.
"It's now up to biomechanics to explain how it performed these feats."
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