Online exhibits : Special exhibits : Fossil footprints

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Fossil footprints through geologic time
IV. Who made these fossil tracks?

By Allison Vitkus, Karen Chin, and Martin Lockley

Dinosaur footprints are the most familiar fossil tracks, but many different types of animals have left their footprints in the rock record over the long course of Earth's history. Check out the images below of fossil tracks in the paleontological collections of the University of Colorado. Can you figure out which types of animals made these fossil tracks?

Click on the hints for clues.

Track mystery 1:
This track (UCM 183.60/US National Park Service specimen)1 was made during the Early Jurassic (around 200 million years ago) in what is now Utah, USA. This track was found at the transition between the Kayenta and Navajo formations, where river sediments were replaced by dune deposits. Who made this track?

This narrow three-toed track is common in Jurassic sediments in this area. The animal that produced this track was predominantly bipedal — that is, it mostly walked on two legs. Claw marks can be seen at the end of the relatively long toes.

Track mystery 2:
This trackway (UCM 167.2/US National Park Service specimen)1 was made in shallow marine sediments during the Triassic Period (between 201 million and 252 million years ago) in what is now Arizona, USA. Who made this track?

Note the drag mark in the center of the tracks. This shows that the animal dragged its tail. Note how similar the individual footprints look — that is, it is difficult to distinguish between tracks from front feet and hind feet. This suggests that the animal may have had more than four legs.

Track mystery 3:
This specimen (UCM 230.86)1 is a replica of a track made in a cave in what is now the state of Missouri, USA. The track was made during the Pleistocene Epoch, which lasted from about 2.6 million to 11,500 years ago. This is relatively recent in comparison to the ages of the rest of the tracks featured on this website! Who made this track?

Do you see any claw marks associated with the toes of this track? Do the pad impressions remind you of familiar tracks made by living animals? Notice how large this track is.

Track mystery 4:
These tracks (UCM 139.93)1 were made on a sand dune during the Permian Period (between 252 and 299 million years ago) in what is now Arizona, USA. Who made these tracks?

There are eight footprints that repeat in these tracks (four on each side). This animal had eight legs! Note that there is no tail drag mark.

Track mystery 5:
This slab (UCM 187.30)1 shows two types of tracks that were made during the middle of the Jurassic Period (roughly 160 million years ago) in terrestrial sediments of what is now Argentina. The lower left-hand corner has a single track of one type of animal, and the other tracks on the slab are part of a trackway of another type of animal. These are natural casts of the tracks — that is, we are looking at a worm's-eye view of the tracks. Who made these tracks?

Look at the scale and note the size of the tracks. The track-makers were not large animals, but one was clearly larger than the other. The track on the left has three toes. The tracks on the right have five toes and show differences between the front and hind feet; this trackway was made by an animal walking on four feet — a quadruped.

Track mystery 6:
The track below (UCM 207.8)1 was found in the Dakota Group, a complex of sedimentary rocks that are around 100 million years old. The Dakota Group rocks were deposited along the western edge of the Western Interior Seaway, the sea that bisected North America during most of the Cretaceous Period (~145 to 66 million years ago). This is a cast of the track, which was found in Colorado, USA. Who made this track?

Notice the long claw drag marks. This suggests that the animal was walking or swimming in shallow water. The claw marks aren't radiating from a central heel area. So even though the track does not show any pad impressions, we can conclude that the foot attached to the claws was relatively wide.

Track mystery 7:
These tracks (UCM 155.44/US Bureau of Land Management specimen)1 were made during the Triassic Period in what is now Colorado. They were found in the Chinle Formation, which was deposited in a terrestrial setting around 225 million years ago. Who made these tracks?

Notice how small these tracks are — less than one centimeter long! These footprints have four or five long toes that end in claws. Mouse over the image; two particularly well-preserved footprints are circled.

Track mystery 8:
The tracks below (UCM 139.97)1 show that an animal moved across a sand dune during the Permian Period (between about 252 and 299 million years ago) in what is now the western United States. Who made these tracks?

Since all the tracks are the same, this animal may have had more than four legs. Also, note that the width of the trackway is about two centimeters. See the faint central line at the left side of the trackway? This shows that the animal dragged its tail or a thickened keel on the underside of its body.

Track mystery 9:
The tracks below (UCM 200/State of Colorado specimen)1 were found at a site now known as Dinosaur Ridge in Colorado, USA. The footprints were found in the Dakota Group, which includes sediments deposited on a coastal plain during the middle part of the Cretaceous Period, about 100 million years ago. Who made these tracks?

Note that the largest track in this photo is about as broad as it is long and has three toes. This particular animal was walking on all four feet when it made these tracks: the large track was made by a hind foot, while the small circular track above it was made by the front foot.

Track mystery 10:
This rock slab (UCM 139.15/)1 shows a trackway made on a sand dune in what is now Arizona, USA, during the Permian Period (sometime between 299 and 252 million years ago). Who made these tracks?

These footprints are rounded with small claw impressions that point forward. This suggests that the track-maker did not walk with a sprawled posture, in the way that lizards and salamanders walk. The fossil record indicates that both dinosaurs and true mammals did not appear until the Triassic Period, which lasted from about 252 to 201 million years ago.

Track mystery 11:
The tracks below (UCM 188.102)1 were found in the Sundance Formation, which includes marine and coastal sediments. These tracks were made around 160 million years ago during the Jurassic Period in what is now Wyoming, USA. Who made these tracks?

There are two differently shaped tracks on this slab, but both of them were made by the same animal. This track-maker left both foot prints and "wing prints" — mouse over the image to see which prints are which. The wing prints were made by the parts of the animal's wings that had short fingers with claws.

Track mystery 12:
This slab (UCM 230.77)1 shows two sets of fossil tracks that were made in what is now Colorado, USA, during the Miocene Epoch, which lasted from around 23 to 5 million years ago. The tracks were found in the non-marine Browns Park Formation. Who made these tracks?

All of the footprints in the trackway on the left are similar and were made by an animal that probably had more than four feet. The trackway on the right was made by an animal that walked on four feet. Note that the front and hind feet in the right trackway are distinctively different in size and placement. Mouse over the image to see which footprints in the trackway on the right were made by the front and hind feet of the track-maker. The foot placement indicates that the animal simultaneously put both front feet down together and also landed with both hind feet together. In addition, note that the distance between the left and right hind feet is much larger than the distance between the two front feet.

Track mystery 13:
These tracks below (UCM 230.243)1 were made in terrestrial sediments in what is now Arizona, USA during the Miocene Epoch, which lasted from around 23 to 5 million years ago. Who made these tracks?

These tracks were made by a large quadrupedal animal. The rounded shape of these tracks is similar to tracks made by modern animals that have hooves with broad fleshy pads. Can you think of a living hoofed animal that uses broad hooves to walk on loose sand?

Track mystery 14:
These tracks (UCM 203.4/State of Colorado specimen)1 were made around 100 million years ago during the middle part of the Cretaceous Period in what is now Colorado, USA. These tracks were found in the Dakota Group, which was deposited in shallow marine and coastal sediments. Who made these tracks?

Note that these tracks have three toes that point forward, and one that points backward. Which types of animals have toes that point backwards? These tracks show a little webbing between some of the toes.

Track mystery 15:
This track (UCM 189.7/US Bureau of Land Management specimen)1 was made in what is now Colorado, USA, during the late Jurassic Period, around 140 million years ago. It was found in the Morrison Formation, which is composed of sediments from ancient lakes and rivers. Note that this is a positive cast of a track — that is, it is the hardened sediment that once filled a footprint impression. Who made this track?

Note that this track has five toes and is broader than it is long. This is a manus (front foot) track. The pes (hind foot) track produced by this track-maker is larger and has a long heel.

 
1UCM refers to the University of Colorado Museum of Natural History. The collection was originally built by the University of Colorado Denver, and was displayed at the Dinosaur Tracks Museum on the Denver campus. The fossil tracks are now housed at the University of Colorado Museum of Natural History in Boulder, Colorado, and the images of these specimens are courtesy of the University of Colorado.