The Grand Canyon is made of sedimentary rock that contains fossils up to 1 billion years old. The most commonly found fossils in the Grand Canyon are sea organisms (crinoids, brachiopods, and sponges). However, several upper layers of rock contain terrestrial, or land-based, fossils, such as dragonfly wing impressions and the footprints of scorpions, centipedes, and reptiles. What do these fossils tell us about the evolution of the geosphere at the Grand Canyon?

The Grand Canyon is made of sedimentary rock that contains fossils up to 1 billion years old. and the several upper layers of rock contain terrestrial, or land-based, fossils, such as dragonfly wing impressions and the footprints of scorpions, centipedes, and reptiles

Answer

The fossils tell us that they have been under ground for many years and  

that they are very hard to find and so you can look for some at The Grand

Canyon

for a different answer set the answer would be because the oxygen in the water had depleted (apex)