Introduction
Grand Canyon National Park in Arizona has a long and diverse fossil record that provides an excellent example of how life has changed through evolution across the expanses of time. This park contains fossiliferous sedimentary rocks that range in age from the Proterozoic (Precambrian) through the Paleozoic and into the Triassic, as well as much younger fossiliferous cave deposits from the last 50,000 years.
Stratigraphic column by Allen Glazner. CC By SA 4.0. Paleozoic fossils photos: NPS photos by Michael Quinn. Stromatolite photo: NPS photo by Carl Bowman. Graphic by Allyson Mathis.
Fossils in Grand Canyon are predominantly found in two geologic occurrences:
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In situ in sedimentary bedrock
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In dry caves
Fossils in Situ within Sedimentary Rock Layers
NPS photo by Michael Quinn.
Fossiliferous sedimentary rocks exposed in Grand Canyon range in age from the Precambrian (Proterozoic) to the Triassic Period of the Mesozoic Era. Most of the sedimentary rocks exposed in the canyon were deposited in the Paleozoic Era. Rocks of the much more ancient Proterozoic Grand Canyon Supergroup can be seen in some areas of the lower reaches of the canyon and contain some fossils, and isolated areas of fossiliferous Mesozoic rocks are exposed within the park boundary but set back from the canyon rim. An understanding of the history of life recorded in the cliffs and slopes of Grand Canyon is dependent on the understanding of the following geologic principles:
Principle of Superposition
This geologic axiom or general law states that in a sequence of layered beds, the lowest bed is the oldest and the highest bed is the youngest, with each bed being younger than the one underneath it and older than the one above it. This principle is based on the processes in which successively younger sedimentary layers are deposited on lower and older layers.
Principle of Faunal Succession
This geologic axiom or general law states that fossil organisms succeed one another in a definite and recognizable order through geologic time as recorded in the rock record. Each geologic formation has a different record of life from that in the formations above it and below it. The principle of faunal succession allows determination of the relative age of rocks using their fossil content.Taken together with the principle of superposition, these principles mean that younger rocks are exposed on the rim of Grand Canyon and that rock units, and the fossils that they contain, get progressively older with greater depth in the canyon. The fossil record recorded by the oldest sedimentary rocks exposed in the canyon is much different than that in the youngest sedimentary rocks in the park.
Proterozoic (Precambrian) Fossils
NPS photo by Carl Bowman.
Stromatolites (“algal” mounds) and microfossils are the only fossils present in the Precambrian Grand Canyon Supergroup, the oldest sedimentary rocks in the park. The oldest fossils in the park are stromatolites, which were particularly abundant in the Mesoproterozoic (1,255-million-year-old) Bass Formation near the base of the Supergroup. Microfossils including Chuaria circularis and vase-shaped microfossils are present in the Neoproterozoic Chuar Group of the Grand Canyon Supergroup.
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Paleozoic Fossils
The Paleozoic Era (“ancient life”) consists of the geologic periods from the Cambrian through the Permian. It began with the Cambrian Explosion when most major animal groups first appeared in the fossil record. Two major extinctions, at the end of the Ordovician and during the Devonian, occurred during the Paleozoic, and are indirectly reflected in Grand Canyon’s fossil record. A third major extinction, at the end of the Permian, marks the end of the Paleozoic and the beginning of the Mesozoic.
The Layered Paleozoic Rocks exposed in Grand Canyon span much of the Paleozoic, although there are no Ordovician or Silurian rocks present in the park because of erosion and non-deposition that have resulted in geologic unconformities between some of the formations in the canyon’s stratigraphic column. Almost all of the rock layers (formations) within the Layered Paleozoic Rocks are fossiliferous and show a changing fossil record due to faunal succession.
Invertebrates are the most common type of Paleozoic fossils found in Grand Canyon, although an especially wide array of trace fossils, especially trackways and trails, are present throughout much of the canyon’s stratigraphy. Vertebrate body fossils, mostly of fish, are known from some units, and plant fossils have been found in rocks that were deposited in terrestrial environments.
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Cambrian Fossils
Photo by John Foster.
Photo by Frederick Sundberg.
Formations in the Tonto Group were deposited in the Cambrian and range between about 510 and 500 million years old. From oldest to youngest, the Tonto Group contains:
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Sixtymile Formation
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Tapeats Sandstone
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Bright Angel Formation
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Muav Formation
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Frenchman Mountain Dolostone
This stratigraphy reflects recent revisions due to ongoing research.
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The Bright Angel and Muav Formations contain trilobite body and trace fossils, as well as body fossils of early brachiopods and echinoderms. The Bright Angel Formation also contains body fossils of other arthropods, including bradoriids. Bradoriids were small bivalved, phosphatic arthropods that went extinct after the Cambrian Period. Trace fossils in the Bright Angel Shale show a remarkable record of invertebrate behavior, including tracks and trails, worm burrows, and feeding traces.
Photos by John-Paul Hodnett.
Because of the absence of rocks from between about 500 and 385 million years, there are substantial differences between the Grand Canyon’s Cambrian fossils and the next-oldest fossils, from the Devonian. The oldest vertebrate fossils known from the park are those of antiarch placoderm fish about 385 million years old, in the Devonian Temple Butte Formation. Antiarch placoderms were a type of heavily armored early jawed fish that did not survive past the Devonian extinction event.
Invertebrate fossils including brachiopods and the oldest coral known from Grand Canyon have also been identified in the Temple Butte Formation. Corals with hard parts first became widespread during the Ordovician, one of the time periods not present in Grand Canyon, so early corals are not present in the canyon.
Mississippian Fossils
NPS photo.
Both the Redwall Limestone and the Surprise Canyon Formation have significant records of invertebrate fossils. The Redwall Limestone was deposited under shallow marine conditions about 340 million years ago during the Early–Middle Mississippian. The Late Mississippian (325-million-year-old) Surprise Canyon Formation was deposited in fluvial, estuarine, and marine environments.
Both formations contain a wide assortment of marine invertebrates that were common in the Mississippian, such as brachiopods, corals, bryozoans, nautiloids, bivalves, gastropods, and echinoderms. Vertebrate fossils include teeth from sharks, a group that diversified during this time interval. Some plant fossils are also known from the Surprise Canyon Formation.
Pennsylvanian Fossils
Photo by Stephen Rowland.
Plants and insects began colonizing the land in the Ordovician, followed by vertebrates in the Devonian. However at Grand Canyon, Paleozoic sedimentary strata older than the Pennsylvanian-Permian Supai Group are almost all marine.
The first Grand Canyon fossils from terrestrial vertebrates are found in Pennsylvanian (320-300 million years old) rocks of the Supai Group. These formations are, oldest to youngest:
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Watahomigi Formation
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Manakacha Formation
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Wescogame Formation
The Watahomigi Formation was deposited in environments ranging from shallow marine to coastal plain. The Manakacha and Wescogame Formations were deposited in fluvial and eolian environments. The Watahomigi contains marine fossils such as brachiopods and shark teeth, whereas the Manakacha and Wescogame Formations contain fossils of terrestrial plants (of horsetails and seed ferns) and vertebrate trace fossils. In 2024, the first Paleozoic vertebrate body fossils from Grand Canyon were reported from the Wescogame Formation.
The Pennsylvanian formations in the Supai Group are the oldest of several successive strata in Grand Canyon that contain significant vertebrate trackways. The Manakacha contains the oldest known tetrapod tracks in Grand Canyon. The Manakacha fossil trackway was discovered in 2016 in a boulder along the Bright Angel Trail. This fossil trackway has great scientific significance as it contains the earliest evidence of vertebrates walking on sand dunes and is among the oldest known terrestrial vertebrate trackways.
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Permian Fossils
NPS Photo by Michael Quinn.
Photos by Linda S. Lassiter.
Strata exposed in the upper portions of Grand Canyon contain information about both marine and terrestrial life during the early to middle Permian, between about 290 and 270 million years ago. In the seas during this time interval, brachiopods, bryozoans, and cephalopods were abundant and diverse, and crinoids and solitary rugose corals were plentiful. On land, the evolution of the amniotic egg allowed amniotes (including the ancestors of today’s mammals and reptiles) to became more abundant relative to amphibians.
The Esplanade Sandstone, the uppermost formation in the Supai Group, as well as the strata above it up to the rim are all Permian in age. From oldest to youngest, the Permian strata of Grand Canyon include:
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Esplanade Sandstone (Supai Group)
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Hermit Formation
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Coconino Sandstone
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Toroweap Formation
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Kaibab Formation
The Esplanade, Hermit, and Coconino were all deposited in terrestrial environments. The Esplanade and Coconino were deposited in eolian environments, and the red beds of the Hermit Formation were deposited a fluvial and coastal plain environment.
Both eolian sandstones are devoid of body fossils but contain plentiful fossil trackways of both vertebrate and invertebrate animals. Trackways in the Coconino Sandstone have been scientifically studied for more than 100 years. The Hermit Formation between the eolian sandstones preserves a more complete ecosystem. The Hermit Formation contains not only invertebrate and vertebrate tracks, but also many species of fossil plants and even a few insect specimens. Insect body fossils are rare in most rocks, and the Grand Canyon fossils capture a moment in the evolution of dragonfly-like and cockroach-like groups.
The Toroweap and Kaibab Formations were deposited in marine environments and contain brachiopods, bryozoans, sponges, mollusks, and other invertebrate fossils, as well as teeth and other fossils of cartilaginous (e.g., sharks) and ray-finned fish.
Mesozoic Fossils
NPS Marsh et al.
The extinction event at the end of the Permian was the largest in the history of life, with 96% of species becoming extinct. Life in both the oceans and on land was dramatically different in the Mesozoic versus the Paleozoic. Although Grand Canyon National Park has an extensive Paleozoic rock record, it has very little in terms of Mesozoic strata. Therefore, unfortunately, Grand Canyon’s fossil record does not provide much information on the changes in flora and fauna following the Permian-Triassic extinction.
The only Mesozoic rocks in the park are limited to isolated Triassic sedimentary rocks belonging to the Moenkopi Formation and Chinle Formation. Both the Moenkopi Formation and the overlying basal Shinarump Member of the Chinle Formation were deposited in continental environments. Within Grand Canyon National Park, the Moenkopi Formation contains trace fossils and the Shinarump Member contains fossil wood in the park. Extensive exposures of these Triassic formations are exposed in other parks such as Petrified Forest National Park in Arizona, Glen Canyon National Recreation Area in Utah and Arizona, and Capitol Reef National Park in Utah provide much information about life in the Triassic.
Pleistocene and Holocene Fossils in Dry Caves
NPS photo by Shawn Thomas.
NPS photo.
In contrast to glimpse into ancient life as preserved in the fossils within the rock walls of the canyon, fossils that have been found in dry caves within the canyon provide information on the organisms that lived in the canyon during the very recent geologic past. Whereas fossils from Grand Canyon’s Paleozoic strata tell of a time when trilobites and other long extinct invertebrates thrived in the oceans and ancient tetrapods walked across sand dunes, fossils found in dry caves provide information on the animals and plants that inhabited the canyon during the late Pleistocene and Holocene during the last 50,000 years. Some of the species found as fossils in dry caves such as California condors are still alive today. Others are extinct, such as Shasta ground sloths, Stock’s vampire bat, and Harrington’s mountain goat.
The canyon’s abundance of caves are mostly in the Redwall Limestone. These caves have provided important habitat sites for a variety of animals including packrats, bats, American cheetahs, ringtails, horses, Harrington’s mountain goat, and Shasta ground sloths. Both body and trace fossils (mostly packrat middens and coprolites or fossil dung) have been recovered in caves. Rampart Cave in the western Grand Canyon had thick deposits of sloth dung and also preserved sloth hair and skin.
Packrat middens found in dry caves are another important source of fossils that provide paleoenvironmental information about the Pleistocene in Grand Canyon. Middens can contain a variety of plant, insect, and vertebrate remains, depending on what was present in the area for the packrat to pick up. They therefore show changes in plant and animal species over time, such as successions of trees and grasses as local climate changes.
Learn More
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NPS—Preserved Remains (Drying, Freezing, Amber, Natural Asphalt)
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Park Paleontology News—Studying the Past and Predicting the Future Using Rat Nests
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Santucci VL and Tweet JS (ed). 2020. Grand Canyon National Park: Centennial paleontological resource inventory (non-sensitive version). Natural Resource Report. NPS/GRCA/NRR—2020/2103. National Park Service. Fort Collins, Colorado.—[IRMA Portal] [NPSHistory.com]
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Grand Canyon National Park (GRCA), Arizona—[GRCA Geodiversity Atlas] [GRCA Park Home] [GRCA npshistory.com]
Last updated: February 28, 2025