Image © P. Sereno and co-authors

SKULL— LIGHT AS A FEATHER

Some of the skull bones of Nigersaurus are so thin that light can pass through them. The fragile skull bones were scanned with X-rays (CT or "computed-tomography").  The digital files from the scans were fed to a special STL (stereolithography) device that generated 3-D plastic replicas of the bones. Then the skull was assembled with the computer-generated replicas.

Photo © M. Hettwer Many of the bones in the skull of Nigersaurus, like this jugal (cheek bone), are so thin that light is able to pass through them.
	Photo © T. Keillor In this photograph, CT-scanned replicas of the fossil bones (yellow) and translucent sculpted missing bones (green) are combined to create a complete skull.

THE TEETH

Photo © M. Hettwer TOOTH BATTERY The teeth in Nigersaurus grew one on top of another in columns within the jaw bones as seen in this close-up of the maxilla upper (jaw bone).

The teeth of Nigersaurus reveal important clues about the eating habits of this plant eater. The jaws of Nigersaurus closed like a ten-inch pair of scissors. Each tooth has a pair of wear facets (surfaces): one wear facet was created when the teeth sheared past each other (surface shown in A below). The other wear facet is on the outside of the tooth, and developed as the jaws gathered plants before slicing them (surface shown in D below).

Photo composite © P. Sereno

The unusually wide jaws of Nigersaurus had more than 60 teeth forming the cutting edge above and below. Stacks of as many as nine replacement teeth are located above each tooth position for a grand total exceeding 500 teeth! There are about 120 tooth positions in the upper and lower jaws. As each tooth wore down, another replacement tooth took its place about once a month.

BRAINS and BRAWN

Image © P. Sereno and co-authors. Multi-colored side view of the brain endocast. Yellow is the olfactory (smell) bulbs. Orange is the "thinking" part, the forebrain (cerebrum); pink is the inner ear with its three canals for balance.

Image © P. Sereno and co-authors. Nigersaurus spent most of its life with its muzzle pointed towards the ground. When the muzzle is pointed foward, as above, the brain is tilted backward, far from its normal orientation

Photo S. Mann These are right femora (thigh bones) from Nigersaurus individuals of different ages. The larger femur belonged to an adult and the smaller femur likely belonged to a one-year old

Like most plant-eating dinosaurs, a forebrain the size of a walnut was all it took for a fruitful lifestyle. Scientists were able to make a cast of the brain of Nigersaurus by filling in the hollow in the braincase of the skull. This cast is called an “endocast,” and it represents the shape of the brain, plus some extra spaces near the brain. By comparing the endocast to that of T. Rex, we know that Nigersaurus had a relatively small forebrain and a poor sense of smell. In addition, the position of the inner ear and its three canals (pink) shows that the skull of Nigersaurus pointed downward most of the time. Nigersaurus grew quickly. When it hatched it was less than 3 feet (1 meter) long and grew in about 15 years to an adult size of 30 feet (9 meters).  The skull and skeleton of Nigersaurus are built of bones that are extremely lightweight.