Keywords: fossils geology paleontology petrified wood tracks trackway national park service nationalparkservice outdoor texture Trace fossils, including worm burrows and trilobite feeding traces (Cruziana) in a block of Bright Angel Shale, Grand Canyon National Park, Arizona. (NPS Photo by Cassi Knight, Paleontology Guest Scientist) Trace fossils, including worm burrows and trilobite feeding traces (Cruziana) in a block of Bright Angel Shale, Grand Canyon National Park, Arizona. (NPS Photo by Cassi Knight, Paleontology Guest Scientist) |