Cambrian Shadows

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Climactichnites

A 150 Year Old Enigma about a 1/2 Billion Year Old Fossil

As you enter the past-life section of the National Museum of Natural History (Smithsonian) one is struck by the fossil cast some eight-foot tall of the mysterious Cambrian fossil Climactichnites. They resemble tracks made by a motorcycle both is size and character. Described by Sir William Logan in 1860, Climactichnites was believed at that time to come from the oldest sedimentary formation known; the Canadian formation is now known to be Upper Cambrian. The fossil caused considerable controversy among paleontologists, and speculation regarding the track maker's identity abounded. Arthropods with soft bodies were denied by the lack of footprints. The possibility of a snail was denied by the V-shaped ridges, and that no known Cambrian snail or worm (even today) can account for the tracks that can be six or more inches wide.

Yochelson and Fedonkin recently hypothsized on the nature of Climactichnites. They posit an 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 microorganisms and its lateral wings to grip for locomotion. In the process of feeding, sand was shoved into the conspicuous periodic rows. The flaps may also have been used for swimming. Since Climactichnites is 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. Thus, Climactinites remains a mystery from the Phylum that perhaps came and went during the Cambrian, or also, the ancestor of other animals that went on to migrate more completely to the land.

More recently, Damrow et. al. have suggested that an alternative explanation for Climactichnites is as a body fossil. Based on new fossils from a sandstone quarry in central Wisconsin they propose that the evidence shown on numerous sandstone slabs is equally compatible with the hypothesis that Climactichnites fossils are body impressions of a gelatinous zooplankter (Zooplankton) that floated into shallow water where they were deposited gently across the extensive tidal sand flats. The picture below links to more pictures of what is surely the most impressive, Climacticnites ever found in the Wisconsin quarry.

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