🎵 Spooky scary skeletons send shivers down your spine 🎵 Eeeek! Its National Fossil Day! While Zion is not well known for its fossil’s, the ones we do have are hugely important to understanding what Zion National Park was like during prehistoric times. Today let’s learn about some of the oldest fossils we have in Zion, how they formed, and imagine what Zion was like during these prehistoric times. Zion’s oldest fossils are found in a sedimentary layer of rock called the Kaibab Limestone, or Kaibab Formation. This formation is the oldest visible rock layer in Zion, being around 270 million years old. It is most easily visible at and around the Kolob Canyons section of Zion. This same rock layer can also be seen at the top of the Grand Canyon, making it the youngest sedimentary rock exposed there. Around 270 million years ago during the Early Permian Period the region where Zion is was not the canyon you think of today, but instead it was the bottom of a vast, shallow, tropical sea as well as coastal flats. How do we know this? Because we can look at the types of rock and fossils found in the Kaibab Formation, and then date them to this time period. The Kaibab Formation consists of marine limestone and siltstone. These marine deposits of the Kaibab Formation are full of fossils! These fossils form by organisms becoming buried by sediment, but usually only the harder parts of the organism are what we see in fossils, as softer parts decompose too quickly. Fossils found in this layer consist of brachiopods & bivalves (which resemble clams), ammonites (shelled cephalopods which resembled the modern Nautilus), bryozoans (not pictured), crinoids (marine animals also known as sea lilies), and everyone’s favorite, trilobites. While these fossils may not be as cool as a T-Rex, they are still very important pieces of the fossil record for Zion National Park. Which one is your favorite? #Nationalfossilday Trilobite photo courtesy of Grand Canyon National Park Ammonite photo courtesy of the Geologic Resource Division Brachiopod photo courtesy of Wind Cave National Park