A spectacular new amber fossil from Myanmar holds the skull of the smallest prehistoric dinosaur ever found: a bird-like creature that lived 99 million years ago and grew no bigger than the smallest birds alive today.  The fossil, described today in the journal Nature, measures just 1.5 centimeters long from the back of the head to the tip of the snout, about the width of a thumbnail. The skull's proportions suggest that the animal was about the same size as a bee hummingbird, which would h