The Changing Life of the Moenkopi

Fern fossil from the Moenkopi Formation
Zion Museum Collection: ZION 635

NPS photo / Scott Ireland

Imagine salty, shallow water lightly lapping the shoreline of a broad tidal flat, while marine organisms scuttle about on the silty bottom. Large reptiles lounge and forage in the afternoon sun along inland drainages. This imagined journey to the 240 million-year-old Moenkopi Formation comes courtesy of Zion's museum collection.

Plant fossils have been found within the Moenkopi in Zion, including the fossilized fern at right. These plants would have grown along the banks of streams that slowly meandered their way to the coastline, or grew in moist areas near shallow lakes.
 
tiny tracks with pointed toes

NPS photo

Only trackways have been found to show us what sort of vertebrates inhabited Utah during the Early Triassic, but they show us that small lizard-like critters, and terrestrial, upright-walking crocodilians, found their way onto these tidal flats. The small tracks in the photo at left are from the lowest portions of the Moenkopi Formation, and are some of the earliest Mesozoic vertebrate tracks known in North America. During this time, the environment was just starting to recover from the largest extinction event in Earth's history, which occurred at the end of the Permian.

South of the park in Arizona, vertebrate bones from early reptiles and amphibians have been discovered, making this an important formation inside the park for possible future discoveries.

 
small impression of a brittle star
Zion Museum Collection: ZION 1939

NPS photo / Jenny McGuire

Marine layers in the Moenkopi reveal a diverse aquatic ecosystem, with body fossils of many plants and invertebrates preserved. Fossils of starfish, brachiopods, crinoids, bivalves, gastropods, and arthropods are found in the Moenkopi's limestone layers.

The photo at right shows "resting traces" of brittle stars--impressions left where these relatives of starfish lay on sediment at the bottom of the shallow sea. These trace fossils were found in the Virgin Limestone Member of the Moenkopi Formation.


Learn more about the Moenkopi Formation

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Last updated: July 6, 2015

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