The First Footprints on Land
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Located in the I39 NB rest area north of Westfield, WI. This EarthCache will take you to a well preserved set of fossil tracks called Climactichnites. Paleontologists believe these are the first footprints cast on dry ground on Planet Earth.
These fossil tracks are classified as Trace Fossils. They consist of non-body remains indicating the activity or behavior of an organism while it is alive. They can represent plants or animals. For example, footprints, trails, stromatolites, coprolites (fossilized feces), eggs, rhizoliths (root-related cementation), borings and burrows can be considered trace fossils. Trace fossils do not include casts or molds of dead shells or other bodily remains. The study of trace fossils is known as Ichnology, and these are classified as Ichnofossils.
There is an entirely separate nomenclature for trace fossils. Each trace fossil has a different name and is not named for the organism.
This EarthCache demonstrates late Cambrian trace fossil tracks from an intertidal setting called Climactichnites.
Never heard of a Climactichnites? Not many people have. First described by Sir William Logan in 1860, Climactichnites was believed at that time to come from the oldest sedimentary formation known: the Canadian formation now known to be Upper Cambrian. This same formation also has been found in Central Wisconsin. Then fossil sites where Climactichnites are found were tidal sandflats during upper Cambrian time, approximately 510 million years ago. As such, the ichnofossils provide the oldes known evidence of animal terrestrial colonization of Earth in the fossil record – the first footprints on land!
These footprints look similar to motorcycle tracks. It normally consists of two parallel ridges separated by chevron-shaped raised cross bars. Ridge height is variable, the tracks may be straight or curvilinear.
Recently, scientists have theorized that Climactichnites were made by a shell-less slug-like animal, twice as long as wide, having a strongly muscled underside with oblique rows of cilia and lateral flaps. The cilia may have been used to sort through sand for micro-organisms and its lateral wings to grip for locomotion. In the prcess of feeding, sand was shoved into the conspicuous periodic rows. The flaps may also have been used for swimming. Since Climactichnites are found on bedding surfaces with ripple marks and mud cracks, it probably spent most of its life moving across the tidal sand flats that were at least periodically above the water.
How Fossil Tracks are formed
Unlike body fossils, which often are best preserved when they are buried rapidly, tracks are more likely to be well preserved when they are buried in a relatively slow, calm manner. For this reason, tracks and bones are seldom found in close association.
The classic scenario is as follows. First, an organism moves along a moist but firm, fine-grained substrate. In this particular case, the mucus extruded by the organism served to stabilize the sand particles. Then the tracks remain exposed for a short while, allowing them to become drier and harder (and thus able to resist damage during subsequent burial). A short time later the prints are gently buried with additional sediment, preferably of a contrasting type (which would allow the layers to separate when later re-exposed). While buried for millions of years, the original sediment hardens into rock. Finally, the tracks are re-exposed in modern times by erosion or other forces. Of course, the tracks also must be found and studied before they are destroyed by weathering, quarry workers, or other dangers. Tracks formed under less ideal conditions tend to be distorted or indistinct, if preserved at all.
The scientific community has recently postulated that what saved the tracks from destruction by wave action was an overlying layer of microbial mats. Microbial sedimentary layers are frequently found in association with Climactichnites in nearby quarries.
Climactichnites remain enigmatic. Was it a slug making the first animal footprints on land as it meandered in the surf, munching on microbial mats? Or, was it a zooplankter that floated ashore, and lured the carnivorous arthropods to shore for dinner?
To log this cache, please e-mail the answers to the following:
*What is the average width of the tracks?
*What is the average number of ripples per linear foot of track?
*Considering the dimensions of these tracks, how big do you think the average slug-like organism was?
*Please post a photo of yourself and your GPSr at these tracks.
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