Secrets of the Chinle Formation
NPS photo / David Tarailo
The sagebrush and cacti-dotted landscape at Zion does not easily render thoughts of lakes, streams, and swamps. During Chinle time, no flowering plants existed; instead, club mosses and ferns grew in freshwater marshes, while horsetails and cycads occupied floodplains. The Chinle Formation's 220 million-year old ecosystem featured conifers, related to modern araucarians like the ornamental Norfolk Pine, which grew to 150 feet with 9-foot widths.
NPS photo / Scott Ireland
When they aged and fell or were toppled by erosion and floods, some of the conifers were buried rapidly by sediments. Deprived of oxygen needed for fast decay, the living woody tissues were slowly replaced by minerals and hardened to stone to form petrified wood. Often, minerals replace the wood quickly enough to preserve the internal cellular structure of the tree, and features like tree rings, bark, and knots are visible.
Learn more about how fossils are made
NPS photo / Jenny McGuire
Quartz is the primary mineral replacing the organic compounds in the wood, but some of the petrified wood at Zion has been replaced with an iron sulfide mineral called pyrite, commonly known as fool's gold.
Plants aren't the only fossil finds from the Chinle Formation at Zion. Within the murky marshes of thick vegetation, a carnivorous creature lurked, heavily protected with armor and built to attack. In this tropical lowland, phytosaurs, with their razor sharp teeth and long snouts, were dominant predators.
Bone fragments and teeth belonging to phytosaurs and the early amphibian Metoposaurus have been recovered from the Chinle Formation in Zion. The phytosaur partial fossil shown here includes the occipital condyle, a part of the braincase which articulated with the upper vertebra.
The museum collection also houses armor plates, called scutes, from the primitive Aetosaurus. Other evidence of ancient life found in the Chinle includes burrows of invertebrates and coprolites (fossilized poop). And after years of uncertainty, the source of a small, mystery tooth has been solved.
Learn more about the Chinle Formation
Return to the Paleontology main page