<p>Dr. Tyler Lyson, Curator of Vertebrate Paleontology for the Denver Museum of Nature & Science, holds open a split concretion and reveals the cross section of a vertebrate skull inside. (HHMI Tangled Bank Studios)</p>

Dr. Tyler Lyson, Curator of Vertebrate Paleontology for the Denver Museum of Nature & Science, holds open a split concretion and reveals the cross section of a vertebrate skull inside. (HHMI Tangled Bank Studios)