GRAND CANYON FOSSILS
Grand Canyon has so much more than pretty scenery. It contains an amazing diversity of rock
formations with an abundance of fossils hidden within. Ancient fossils preserved in the rock layers range
from algal mats and microfossils from Precambrian Time 1,200 million to 740 million years ago to a
multitude of body and trace fossils from the Paleozoic Era 525-270 million years ago.
What about dinosaur fossils? Not at Grand Canyon! The rocks of the canyon are older than the oldest
known dinosaurs.
Sedimentary rock contains fossils because it was built up layer upon layer, often trapping and preserving
animals, plants, footprints, and more within the layers of sediment. If all the conditions are right, fossils
are formed as the layers of sediment turn into rock.
With 32% of Earth’s geologic history and one billion years of fossil life found at Grand Canyon, this is a
great place to study ancient environments, climate changes, life zones, and the geologic processes that
formed the landscape as we see it today.
Marine Fossils
With marine environments creating many of the sedimentary rock layers in the canyon over the past
525 million years, marine fossils are quite common. Species changed over time, but similar fossils can be
found in most of the marine-based rocks at Grand Canyon.
Stromatolites
The oldest fossils at Grand Canyon are 1,200 million to 740 million years old. Stromatolites are the
limestone structures formed by photosynthesizing bacteria called cyanobacteria. They created layers of
alternating slimy bacteria and sediment in very shallow water, dominating shallow seas until predators,
such as trilobites, came into the picture. Today stromatolites only live in a few shallow ocean areas with
high salinity. The salinity deters predation and allows the stromatolites to survive.
Trilobites
Grand Canyon’s oldest trilobites are found in the Tonto Group, which is between 525 and 505 million
years old. These fossils are arthropods, or joint-footed animals, with a segmented body of hinged plates
and shields. They could curl up into a ball for protection, sometimes fossilizing as a "rolled" trilobite. Like
arthropods today, trilobites molted as they grew, shedding their old exoskeleton. These molts could
fossilize, so one animal could leave several different sized fossils behind.
Even though trilobites were relatively primitive animals, they had amazingly complex eyes.
Terrestrial Fossils
The mudstones and siltstones of the Hermit Shale and Supai Group were laid down by a meandering
system of rivers and streams in a semi-arid climate about 280 million years ago. The sand grains of the
Coconino Sandstone were deposited by wind across large coastal sand dunes about 275 million years
ago.
Leaves
In the red layers of the Hermit Shale, plant fossils can be found in the mudstone and siltstone left behind
by an ancient river system. Indicated by these fossils is a semi-arid climate, with drought-adapted seed
ferns, horsetails, small pines, ginkgos, and a noticeable absence of true ferns.
Dragonflies
Oxygen in the atmosphere during the time of the Hermit Shale deposition was in greater abundance
than today, probably 35% compared to the present day 21%. Increased oxygen meant larger insects,
explaining the eight-inch wingspan of a dragonfly wing impression fossil found in the Hermit Shale.
Recent Fossils
The semi-arid climate and cool temperatures deep within canyon caves have combined to create a
perfect environment for preservation of more recent fossils. Pleistocene and Holocene remains have
been unearthed within many of these caves, including 11,000 year old sloth bones, dung and hair,
California condor bones and egg shell fragments, and pack rat middens.