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Fossil Eggshell home
The geography of fossil tracks

By Laura E. Wilson1,2, Karen Chin1,2, Frankie D. Jackson3, and Emily S. Bray1

1Museum of Natural History, University of Colorado, Boulder, Colorado, USA; 2Department of Geological Sciences, University of Colorado, Boulder, Colorado, USA; 3Department of Earth Sciences, Montana State University, Bozeman, Montana, USA

Continental drift animation Animals have been making tracks on Earth for over 540 million years. This is how long animals have been walking, scurrying, or slithering through loose sediment on this planet. During the long history of fossil track creation, environments on Earth have gone through many changes. Continents have moved and sea levels have risen and fallen many times — click to see an animation of the movements of the continents over the last 750 million years [insert animation]. As a result, many of the oldest rocks on Earth have been lost through erosion and tectonic plate movements. Nevertheless, fossil tracks have been found all over the world.

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Earliest signs of locomotion
Early locomotion trace from the Ediacaran Period, found in Newfoundland, Canada. The fossil trail stretches from the lower left to the upper right sides of the photo (Image from Liu et al. 2010).
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Evidence for single-celled life on Earth stretches back over 3.5 billion years (Mojzsis et al. 1996). However, the oldest evidence for macroscopic animals moving about on Earth is from the Ediacaran Period, which lasted from around 635 to 541 million years ago. The trails they made aren't footprints, but are instead more likely the results of creatures wriggling along the surface of the sediment. Fossils from the Ediacaran include bizarre life forms that are poorly understood. Many of these fossils are narrow and long, and it can be difficult to distinguish fossil trails from fossils of the animal's body itself. Nevertheless, some of these fossils do seem to be tracks and provide some of the earliest evidence for animal locomotion on Earth. One is a specimen of Cochlichnus, a sinuous trail found in Namibia and thought to have been made by a worm-like animal (Jensen et al. 2006). Even older evidence of locomotion was found in Newfoundland, Canada. This fossil trail is thought to have been made around 565 million years ago in ocean sediments. The animal that made this track is unknown, but one group of scientists has suggested that the fossil trace is similar to trails made by sea anemones (Liu et al. 2010).

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Fossil tracks and trails
Left: Ichniotherium, cast of fossil tracks left by an early diadectid tetrapod (an animal that walked on four feet) during the Permian Period of what is now Germany (UCM 139.98; Lockley and Meyer 2000, Voight et al. 2007). Right: Cochlichnus, fossil trails possibly left by a type of worm (UCM 230.38; Metz 1998). Often it's difficult to tell exactly what kind of organism made a trace fossil.

Tracks are individual foot prints. But some animals don't have feet at all! Worms and other footless organisms make trails on sediment surfaces instead of tracks. Fossil tracks and trails are both examples of trace fossils; trace fossils record evidence of an organism's activity, whereas body fossils provide evidence for the morphology (form) of ancient organisms.
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What depositional environments are tracks commonly found in?
We tend to find more fossil tracks in sediments deposited in certain environments. As discussed in the section, burial of tracks improves their chances of fossilization. Thus, tracks made near bodies of water and sand dunes are more likely to be buried before they are destroyed than are tracks made in other environments. Sedimentary rocks preserve records of past habitats. The types of rocks in an area give us clues as to whether the ancient environment was once an ocean shoreline, shallow lake sediments, sand dunes or another habitat.

Tracks are commonly found in areas associated with streams or rivers. Sediments deposited by rivers and streams are called fluvial deposits and include mud, silt, and sand. The track below was made in mud thought to have been deposited by a flooding river; the thin layer of mud was found above sandstone beds typical of river bank deposits. This particular type of track is called Dromaeopodus shandongensis and was probably made by a dinosaur closely related to Tyrannosaurus and modern birds.

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Cast of Dromaeopodus shandongensis, a track made by a theropod walking along a river after a flood. This track was made in what is now Shandong, China during the early Cretaceous Period. Most theropod tracks have three toes, but this one only left impressions of two toes. This is because one toe, which had a much larger claw than the others, was held up when the animal walked (UCM 214.112; Li et al, 2008).

It is also common to find tracks in sediments that were deposited on the shores or in the shallow waters of lakes (called lacustrine sediments). Below are tracks of a web-footed bird found in the Green River Formation of Utah, USA. The Green River Formation is made up of lake sediments deposited during the Eocene Epoch and is known for containing many fossil fish skeletons.

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Fossil tracks of a bird with webbed feet, walking in shallow waters of a lake (UCM 230.14).

Fossil tracks associated with marine environments were formed along the shores or in shallow waters of the ocean. The trace below is called Isopodichnus and was probably made by an an isopod or similar crustacean. This trail was made in a shallow sea in North America during the Jurassic Period, when a series of inland seas flooded central western North America (Anderson and Lucas 1992).

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Isopodichnus arthropod traces in shallow marine sediment (UCM 187.29) These traces were associated with pterosaur tracks!

Tracks can also be found in eolian deposits. These are sediments that were moved by wind instead of water. Below is a type of trackway called Paleohelcura, which is thought to have been made by a scorpion (Azain and Wright 2005). The sediment was deposited in sand dunes during the Permian Period (Weimer and Erickson, 1976).

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Paleohelcura, a possible scorpion trackway on ancient sand dune deposits (UCM 139.97).

Fossil tracks from around the world
Today, tracks have been found on every continent — including Antarctica! But since the continents have moved over time, fossil tracks may have been made on continents that were in a different latitude or orientation on Earth than they are today. Fortunately, geologists have been able to reconstruct the approximate positions of the continents over time, and can help us figure out where on Earth the original fossil footprints were made. The following are examples of fossil track sites that have been discovered on each of the current continents.

North America
During the Cretaceous Period (~145-66 million years ago; Walker et al. 2012) global sea levels were high, and a body of water called the Western Interior Seaway split North America into eastern and western land masses. Large herds of dinosaurs left tracks as they moved north and south along the coastal plain of the western shoreline of the Western Interior Seaway. This extensive series of track-rich coastal plain sediments is called the Dinosaur Freeway (Lockley and Hunt 1995).

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Map of North America during the Cretaceous Period, when the Western Interior Seaway split the continent. The Dinosaur Freeway was on the west side of the seaway, in what is now the United States. The star marks Dinosaur Ridge, a site where dinosaurs made tracks on the shore when the Western Interior Seaway was not as extensive as in this image. Map courtesy of the United States Geological Survey.

The Dinosaur Freeway consists of over 80 tracksites in the United States ranging from northern New Mexico to northern Colorado. These sites preserve tracks made by animals of varying sizes, and many indicate that the dinosaurs that made them were moving parallel to each other. Most of the tracks were made by herbivorous ornithopod dinosaurs, though some were made by bipedal theropod dinosaurs, shorebirds, and crocodilians.

One easily accessible fossil site along the Dinosaur Freeway is Dinosaur Ridge near Denver, Colorado. This area contains many ornithopod tracks and theropod tracks. The tracks are found in different layers of sandstone, indicating that the animals walked in same area at different times (Lockley and Hunt 1995).

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Cast of Caririchnium, an ornithopod dinosaur track from Dinosaur Ridge, a site along the Dinosaur Freeway in the western United States (UCM 209.1).

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Early encounters with fossil footprints
Cast of a track made by a bipedal, meat-eating theropod dinosaur from the early Jurassic Period in the western United States (UCM 179.10). Tracks like this are mentioned in Hopi traditional lore (Mayor 2005).

What would you think if you saw some strange tracks that were apparently produced by an animal unlike any you had seen before? These tracks even more perplexing because they were hardened into stone! People around the world observed fossil tracks long before modern paleontologists began to study them. Some ancient peoples assumed that strange lithified tracks belonged to animals that were still alive, but lived far away. Other people believed that such tracks belonged to supernatural creatures or spirits. In North America, many Native peoples have stories and traditions related to fossil tracks. For example, images very similar to theropod dinosaur tracks have been seen on the costumes of Hopi people performing the Snake Dance, an ancient rain-related ritual. One version of Hopi traditional lore is that the three-toed tracks found in rocks were left by the Kachina spirit who sends down rain. Dinosaur tracks in the area are often hard to see, but are always more visible when water collects in them after a rainstorm (Mayor 2005).
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An interesting European dinosaur track site can be found near Fátima, Portugal. The tracks were found in the bottom of the Pedreiros do Galinha limestone quarry in 1994. They were made in shallow marine sediments during the middle of the Jurassic Period, about 170 million years ago (dos Santos et al. 2008, Lockley and Meyer 2000, Walker et al. 2012). Large, long-necked, herbivorous dinosaurs, called sauropods, apparently produced the footprints. These Galinha sauropod tracks are notable for being particularly large and well-preserved, and the site was dedicated as a national monument by the Portuguese government in 1996 (Monumento Natural das Pegadas dos Dinossáurios da Serra de Aire). Visitors to Fátima can see the tracks and learn more about them at the visitor center.

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Left: Map of the world during the early Jurassic Period, over 20 million years before the tracks at the Galinha site in Portugal were made. The red star denotes Portugal on this map, an island situated between the rest of Europe, North America, and Africa. Image by C.H. Scotese. Right: Sauropod tracks at the Galinha fossil track site near Fátima, Portugal. Photograph by Ines Saraiva.

South America
Many spectacular fossil tracks were found in Bolivia high in the Andes. These tracks were made near the end of the Cretaceous Period around 65 million years ago. Since then, geologic forces tilted the track beds upward forming a steeply angled wall. Workers in a cement quarry discovered the site in 1994, and now over 5,000 dinosaur tracks have been found there in what is now Parque Cretácico in Cal Orck'o. The site includes tracks made by ankylosaurs, armored herbivorous dinosaurs that walked around like prehistoric tanks. Ankylosaur tracks were thought to be much rarer before the discovery at Cal Orck'o; for many years, people doubted ankylosaurs had lived in South America at all. Theropod and sauropod tracks have also been found at the site, as well as bones from turtles, fish, and crocodilians (Lockley et al. 2002, McCrea et al. 2001). Unfortunately a large section of the wall with the best trackways fell down in 2010. However photographs of the site are among the most spectacular dinosaur track images ever taken.

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Left: Map of the world near the end of the Cretaceous Period, 66 million years ago. The star marks what is now Bolivia. Image by C.H. Scotese. Right: Fossil tracks at Cal Orck'o, Bolivia, tilted at a steep angle. Photograph by Jerry Daykin from Cambridge, United Kingdom.

The Laetoli Beds, in northern Tanzania, preserve a series of track sites famous for the footprints of early hominins (a group that includes humans and our close ancestors). The Laetoli tracks demonstrate an unusual type of track fossilization because they were preserved in volcanic ash about 3.6 million years ago. These footprints are much younger than most of the fossil tracks described on this website. This underscores the fact that hominins have had a relatively short history on Earth compared to most other animals. At the time they were found, the Laetoli tracks provided the oldest evidence of hominins that walked on two legs (Leakey and Hays 1979). There has been debate about which species actually made the Laetoli tracks; Australopithecus afarensis (aka, "Lucy") may be the best track-making candidate (White and Suwa 1987). Fossil tracks of birds, invertebrates, and many mammals (including hares, horses, and hyenas) have also been found in the Laetoli Beds (Leakey and Hays 1979).

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Left: Map of the modern world. The current position of the continents is very close to where they were 3.6 million years ago. The star marks Tanzania, where the Laetoli tracks were found. Image by C.H. Scotese. Right: Cast of the Laetoli hominin tracks on display at the Smithsonian National Museum of Natural History in Washington, D.C., United States. Photograph by Tim.

The Haenam fossil site in South Korea hosts over 500 dinosaur tracks, 400 pterosaur tracks, and thousands of web-footed bird tracks, some of the oldest of their kind known. The fossil tracks are found in the Uhangri Formation, which was deposited during the mid to Late Cretaceous between about 100 and 72 million years ago (Huh et al. 2003, Walker et al. 2012). Most of the dinosaur tracks at this site were made by ornithopods, though some tracks are thought to have been made by sauropods. The pterosaur tracks include hind foot impressions as well as hand prints. Pterosaurs (flying reptiles related to dinosaurs) are thought to have walked at least some of the time on all fours, with their wings folded up so their hands could be on the ground (Lockley and Meyer, 2000). The site was named as a national monument in 1998, and Uhangri Dinosaur Museum is located near the tracks.

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Left: Map of the world during the Late Cretaceous Period. Image by C.H. Scotese. Right: Cast of Uhangrichnus, webbed footed bird tracks from the Upper Cretaceous Uhangri Formation of South Korea (UCM 214.143).

The Lark Quarry "dinosaur stampede" in Australia presents another example of a site with many Cretaceous dinosaur tracks. The tracksite was discovered in the 1960's and is now preserved in the Lark Quarry Conservation Park. Some scientists think that the thousands of fossil footprints represent a stampede of a mixed group of small dinosaurs reacting to the presence of a large carnivorous theropod dinosaur. Other scientists, however, think that Lark Quarry was just a well-used route for dinosaurs along the shallow waters at the edge of a river (Romilio et al. 2013). The Lark Quarry Dinosaur Trackways site is about 110 km from Winton in central Queensland.

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Left: Map of the world during the late Cretaceous Period. The star marks the area of Lark Quarry Dinosaur Trackways site. Image by C.H. Scotese. Right: Photograph of some of the Lark Quarry Dinosaur Trackways. The large tracks in the left side of the photo are thought to have been made by a large predator. A building has been erected around the fossils to protect them.

The continent of Antarctica used to be further north and much warmer. Unfortunately, Antarctica's current frozen climate makes it difficult to find many fossils there. Most of the fossil tracks found so far in Antarctica were made by invertebrates. However fossil vertebrate bones and tracks, have also been discovered on the continent.

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Left: Map of the world during the Triassic Period, when many of today's continents were part of a supercontinent called Pangea. Notice how Antarctica was connected to Africa and India. Image by C.H. Scotese. Right: Early synapsid track from the Triassic Period of Antarctica. Image from MacDonald et al. 1991.

An international team of scientists found fossil vertebrate tracks in the Queen Alexandra Range of Antarctica during an expedition to the continent in 1990-1991. These tracks were made during the Triassic Period and were probably made by early synapsids, a group that includes mammals (MacDonald et al. 1991). The trackmaker is believed to be the protomammal a close relative of early mammals???, Lystrosaurus. Fossil bones of Lystrosaurus have been found in Antarctica as well as in Africa and India (Elliot et al. 1970). The distinctive distribution of this terrestrial animal provided important early evidence for the fact that the continents have moved over time.

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Reconstruction of previous continent locations during the Triassic Period using ranges of certain fossils as evidence. Fossils of Lystrosaurus, for example, have been found in Antarctica, Africa, and India. Since this animal was terrestrial, the fact that it is found on these continents offered evidence that these land masses were once connected. Image courtesy of the United States Geological Survey.

Anderson, O.J., and S.G. Lucas. 1992. The Middle Jurassic Summerville Formation, northern New Mexico. New Mexico Geology 14(4):79-92.

Azain, J., and J. Wright. 2005. Effects of slope and temperature on the morphology of experimental spider and scorpion trackways. Geological Society of America Abstracts with Programs 37(6):6.

dos Santos, V.F., C.M. da Silva, and L.A. Rodrigues. 2008. Dinosaur track sites from Portugal: Scientific and cultural significance. Oryctos 8:77-88.

Metz, R. 1998. Nematode trails from the late Triassic of Pennsylvania. Ichnos 5(4):303-308.

Fortey, R.A., and A. Seilacher. 1997. The trace fossil Cruziana semiplicata and the trilobite that made it. Lethaia 30(2):105-112.

Huh, M., K.G. Hwang, I.S. Paik, C.H. Chung, and B.S. Kim. 2003. Dinosaur tracks from the Cretaceous of South Korea: Distribution, occurrences, and paleobiological significance. Island Arc 12(2):132-144.

Jensen, S., M.L. Droser, and J.G. Gehling. 2006. A critical look at the Ediacaran trace fossil record. Pp. 115-157 in S. Xiao and A.J. Kaufman (eds.), Neoproterozoic Geobiology and Paleobiology. Springer, Dordrecht, The Netherlands.

Leakey, M.D., and R.L. Hay. 1979. Pliocene footprints in the Laetoli Beds at Laetoli, northern Tanzania. Nature 278:317-323.

Li, R., M.G. Lockley, P.J. Makovicky, M. Matsukawa, M.A. Norell, J.D. Harris, and M. Liu. 2008. Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China. Naturwissenschaften 95(3):185-91.

Lieberman, B.S. 2002. Phylogenetic analysis of some basal Early Cambrian trilobites, the biogeographic origins of Eutrilobita, and the timing of the Cambrian Radiation. Journal of Paleontology 76(4):692-708.

Liu, A.G., D. McIlroy, and M.D. Brasier. 2010. First evidence for locomotion in the Ediacara biota from the 565 Ma Mistaken Point Formation, Newfoundland. Geology 38(2):123-126.

Lockley, M.G., and A.P. Hunt. 1995. Dinosaur Tracks and Other Fossil Footprints of the Western United States. Columbia University Press, New York. 360 pp.

Lockley, M.G., and C.A. Meyer. 2000. Dinosaur Tracks and Other Fossil Footprints of Europe. Columbia University Press, New York. 360 pp.

Lockley, M.G., A.S. Schulp, C.A. Meyer, G. Leonardi, and D.K. Mamani. 2002. Titanosaurid trackways from the Upper Cretaceous of Bolivia: Evidence for large manus, wide-gauge locomotion and gregarious behavior. Cretaceous Research 23:383-400.

MacDonald, D.I.M., J.L. Isbell, and W.R. Hammer. 1991. Vertebrate trackways from the Triassic Fremouw Formation, Queen Alexandra Range, Antactica. Antarctic Journal of the United States 26(5):20-22.

Mayor, A. 2005. Fossil Legends of the First Americans. Princeton University Press, Princeton, New Jersey.

McCrea, R.T., M.G. Lockley, and C.A. Meyer. 2001. Global distribution of purported ankylosaur track occurrences. Pp. 413-454 in K. Carpenter (ed.), The Armored Dinosaurs. Indiana University Press: Bloomington, Indiana.

Mojzsis, S.J.,G. Arrhenius, K.D. McKeegan, T.M. Harrison, A.P. Nutman, and C.R.L. Friend. 1996. Evidence for life on Earth before 3,800 million years ago. Nature 384(7):55-59.

Romilio, A., R.T. Tucker, and S.W. Salisbury. 2013. Reevaluation of the Lark Quarry Dinosaur Tracksite (Late Albian-Cenomanian Winton Formation, Central-Western Queensland, Australia): No Longer a Stampede? Journal of Vertebrate Paleontology 33(1):102-120.

Voight, S., D.S. Berman, and A.C. Henrici. 2007. First well-established track-trackmaker association of Palezoic terapods based on Ichniotherium trackways and diadectid skeletons from the Lower Permian of Germany. Journal of Vertebrate Paleontology 27(3):553-570.

Walker, J.D., J.W. Geissman, S.A. Bowring, and L.E. Babcock (compilers). 2012. Geologic Time Scale v. 4.0. Geological Society of America.

Weimer, R.J., and R.A. Erickson. 1976. Lyons Formation (Permian), Golden-Morrison area, Colorado. Pp. 123-138 in R.C. Epis and R.J. Weimer(eds.), Studies in Colorado Field Geology. Professional Contributions of Colorado School of Mines 8.

White, T.D., and G. Suwa. 1987. Hominid footprints at Laetoli: Facts and interpretation. Physical Anthropology 72(4):485-514.

Wolfe, K.J. 1990. Trace fossils as paleoenvironmental indicators in the Taylor Group (Devonian) of Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology 80:301-310.

Images we need permission for:
Liu, A.G., McIlroy, D., Brasier, M.D. 2010. First evidence for locomotion in the Ediacara biota from the 565 Ma Mistaken Point Formation, Newfoundland: Geological Society of America 38(2):123-126.
-photo of Ediacaran fossil trail

MacDonald, D.I.M., Isbell, J.L., Hammer, W.R. 1991. Vertebrate trackways from the Triassic Fremouw Formation, Queen Alexandra Range, Antactica: Antarctic Journal of the United States 26(5):20-22.
-photo of Antarctica synapsid track

Scotese, Paleomap project
-maps and animation – maybe just ask Berkeley



What fossil eggshell tells us

NSF logo This site was funded by the National Science Foundation under award no. 0646420.

The authors would like to thank Toni Culver, Vertebrate Collections Manager, University of Colorado Museum of Natural History, for her help with the organization of the Karl Hirsch eggshell collection and accumulating data and images for the website; and Jack Horner, Curator of Paleontology, Museum of the Rockies, for suggestions on how to make the information in the website more accurate and accessible.