1.   And animal skull fossils sometimes yield tantalizing evidence of transitional metabolic natures.

2.   One difficulty was the scarcity of sphenoid bones, which are fragile and often are not preserved in skull fossils.

3.   But the teeth and skull fossils that unmistakably mark it as a higher primate were found more recently.

4.   The system lets researchers see inside skull fossils and reconstruct the skull from fragments, allowing a precise measure of brain size.