Climactichnites is an enigmatic, late Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 fossil formed on or within sandy tidal flats around .
It has been interpreted in many different ways in the past, but is now known to be a trace fossil

Trace fossil

Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...

 of a slug

Slug

Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...

-like organism, thought to have moved by crawling on near-shore or on-shore surfaces or burrowing into the sediment.

Morphology

There are two species within this ichnogenus, C. wilsoni and C. youngi. C. wilsoni consists of paired lateral ridges between which are undulating bars and furrows oriented at an angle to the direction of travel, whereas
C. youngi lacks the paired lateral ridges and consists only of undulating transverse bars and furrows. The fossils range from 2 to 30 cm in width, and individual imprints reach 69 cm in length; chains may exceed ten feet in length. This makes Climactichnites by far the largest Cambrian trace fossil. Climactichnites represents the trail of the animal; its resting traces are termed Musculopodus and are sometimes found at the beginning of a trail.

Occurrence

Currently, Climactichnites is known only from North America (Missouri, New York, and Wisconsin in the United States, and Quebec and Ontario in Canada), portions of which were submerged under a shallow equatorial sea during the Cambrian Period. The fossil is found in fine- to coarse-grained sandstones which represent sandy, intertidal beach deposits. Microbial mats probably enabled the trace to be preserved.

Interpretation

Early attempts to interpret the fossil as the body of an alga or siphonophore are easily falsified, and it is now thought to represent the trail of an organism moving on top of or through the sediment. The animal apparently had a muscular foot and moved by extending either side of its body alternately (sometimes both sides may have been extended in unison) to produce the v-shaped transverse bars. Certainly the animal lacked any appendages, as is evidenced by cross-cutting relationships of the trail with sedimentary structures such as ripple marks. While the identity of the trace-maker remains conjectural, Climactichnites was most likely produced by a large slug-like mollusc; modern gastropod molluscs have been observed to produce similar traces. Since it is often associated with surface-produced sedimentary structures, it may have been produced by one of the earliest animals to move about on land. The binding effect of microbial mats on the sediment surface is believed to have contributed to the exceptional preservation of Climactichnites trails.

External links

English translation

Includes additional photographs and information on Climactichnites from the exceptional Blackberry Hill localities.

• Wisconsin quarry

Cambrian jellyfish, Climactichnites and arthropod tracks

• Blackberry hill fossils

Discusses a major source of Climactichnites trackways. With useful photograph slideshow.