The Climactichnites trackway constitutes evidence of the first time any animal tentatively reached out from the sea to claim the land. The attempt was unsuccessful, but deserving of recognition

The first director of the Geological Survey of Canada lived very simply. Sir William Logan occupied a single room at the Survey offices at 76 St. Gabriel Street in the heart of old Montreal. This room served as his office and bedroom, as well as for reception and storage. One wall was entirely covered by an immense slab of sandstone displaying six overlapping tracks. Each track was 15 cm wide and marked by a chevron cross pattern repeated with almost machine-like regularity between crenulated marginal ridges. In all, the trackway looks disturbingly like dirt-bike tire tracks.

This trackway came from the Potsdam Formation at Perth, halfway between Kingston and Ottawa. These rocks were thought to be some of the oldest fossiliferous sedimentary rocks anywhere -- now they are known to be Upper Cambrian. In 1860 Logan described and named this trackway Climactichnites. The presence of this large and strikingly patterned trackway in such ancient rocks caused quite a stir among paleontologists who immediately began to speculate on the identity of the track maker. Some suggested arthropods -- either horseshoe crabs or trilobites -- or perhaps worms; others thought mollusks such as snails or chitins were responsible. However, none of these is likely. An arthropod would leave discrete footprints and a snail or chitin a smooth trail quite unlike the high chevron ribs and crenulated lateral ridges of Climactichnites. Size also presents a problem. All Cambrian snails are smaller than 2 cm, and no fossil worm is as wide as even a small Climactichnites. But mollusks received renewed support when ovoid slug-like impressions were discovered at the end of some exceptionally preserved trails in New York.

Recently, Yochelson and Fedonkin set out to reconstruct the anatomy of this animal from the nature of its trackway. The animal must have been about twice as long as wide, covered by tough upper skin with its lower surface composed of a strongly muscled sole with oblique rows of cilia. On each side hung a pair of wing-like flaps. The animal used its cilia to sort through sand grains for microorganisms and its lateral wings to grip the sediment. In the process of feeding, the sand was packed into oblique rows.

Although the Climactichnites animal was able to swim with its lateral flaps, it spent most of its life moving across the tidal sand flats that must have been periodically exposed because the track ways occur on bedding surfaces with ripple marks and mud cracks. Climactichnites, therefore, records a signal event -- the first time that any animal reached out from the sea to move onto the land. The attempt was ultimately unsuccessful, but it deserves acknowledgement, at least by land dwellers such as ourselves. The animal itself appears to belong to an unnamed phylum that lived briefly on the vast tidal sand flats that existed in eastern North America around 500 million years ago.

Further reading:

Yochelson, Ellis and Fedonkin, Mikhail.
1993:  Paleobiology of Climactichnites, an enigmatic Late Cambrian fossil. Smithsonian Contributions to Paleobiology, No. 74.