Chris Retzlaff (USA)
The Redhill Ridge space in Park County, Colorado is a hogback composed of Dakota Sandstone. This fine-grained, Cretaceous sediment – close to the city of Fairplay – accommodates trace fossils (Figs. 1 and 2) that help palaeontologists understand what the environment was like there, more than 65 million years ago.
Trace fossils, also called ichnofossils, are like fossils of any kind – they are traces of organisms preserved in the Earth’s crust from prehistoric times. They can be important to palaeontologists for many reasons:
- They capture paleo-behaviour of prehistoric creatures revealed through the traces they left behind, such as burrows, tracks, trails, coprolites (excrement), and boreholes (Pannell, 2004).
- They also provide information on the climate and the environment they were formed in.
- They can reveal many important facts about the rock they are embedded in, such as the sedimentary environment, the rate of deposition and if water flowed on or near the rock (Kusky, 2005).
Generally, if the maker of the trace is not found with it, it is difficult or impossible to know what organism made it. For instance, entirely different organisms may produce identical traces. As a result, trace fossils are classified into either genus or specie groups – ichnogenera and ichnospecies respectively – which do not relate directly to the organisms that created them. However, for the most part, the only way to truly determine what organism created a trace fossil is to find the actual fossilised remains, or body fossils, of the organism that made the traces in direct association with those traces.
The Redhill Ridge trace fossils hold some interesting clues as to what organisms lived there:
- During the Cretaceous Period, the area near present day Fairplay was near the shore of a huge inland sea – the Western Interior Seaway (Chronic and Williams, 2002). This means that whatever creature made these fossils in the Redhill Ridge area lived in shallow water near the shore.
- The trace fossils show that the maker could dig a system of burrows and tunnels in the sand.
- It is possible to assume that the organism’s habitat was wet because of its ability to burrow in sand. That is, the tunnels would collapse without water.
- From measurements of the actual trace fossil specimens, it is easy to tell their widths range from 3mm to 5mm.
Using these clues, it is possible to hypothesise that the organisms that made these traces were worms or similar animals.
The Redhill Ridge area is rich in trace fossils and these fossils continue to aid palaeontologists to understand the local environment as it was during the Cretaceous.
At the time he wrote this article, Chris Retzlaff was 13 years old and in the eighth grade. He lived in the Denver metro area and was a junior member of the Colorado Springs Mineralogical Society.
References
Chronic, H., and Williams, F., 2002. Roadside Geology of Colorado. Missoula, Montana: Mountain Publishing. Company.
Pannell, M., 2004. “Fossil and Fossilization.” The Gale Encyclopedia of Science. Detroit: Gale Virtual Reference Library.
Kusky, Timothy, 2005. “Biogenic Sediment.” Encyclopedia of Earth Science. New York: Facts On File, Inc.
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