| An explorer of the Mesozoic Era examines fossiliferous limestones and shales belonging to the lower Jurassic part of the Upper Triassic-Lower Jurassic Gabbs Formation in Ammonite Canyon, Nevada; the rocks here are roughly 198 to 196 million years old (Hettangian Stage of the Jurassic), deposited just after the great mass extinction at the close of the Triassic Period (about 200 to 199 million years ago). |