Summary
Cruziana is a trace fossil (fossil records of lifeforms' movement, rather than of the lifeforms themselves) consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension. It is found in marine and freshwater sediments.[1] It first appears in upper Fortunian rocks of northern Iran and northern Norway.[2] Cruziana has been extensively studied because it has uses in biostratigraphy (specific scratch patterns are unique to specific time intervals),[3] and because the traces can reveal many aspects of their makers' behavior.
| Cruziana | |
|---|---|
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| Cruziana, fossil trackways of trilobites. | |
Trace fossil classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita |
| Ichnogenus: | †Cruzianad'Orbigny, 1842
 Cruziana is typically associated with trilobites but can also made by other arthropods.[1] Cruziana appears in non-marine formations such as the Beacon Supergroup that would have been unsuitable environments for trilobites,[1] and in Triassic sediments that were deposited after trilobites became extinct at the end of the Permian Period.[4] Cruziana traces can reach 15 mm across and 15 cm in length, with one end usually deeper and wider than the other.[1] The burrow may begin or end with a resting trace[5] called Rusophycus, the outline of which corresponds roughly to the outline of the trace-maker, and with sculpture that may reveal the approximate number of legs, although striations (scratchmarks) from a single leg may overlap or be repeated. Cruziana tenella, and conceivably other ichnospecies, appears to have been formed by the concatenation of a series of Rusophycus traces, suggesting that Cruziana is a feeding trace, rather than a locomotory trace formed by burrowing within a layer of mud as historically believed.[6] The ichnogenus Diplichnites may be produced where the trackmaker sped up.[citation needed] Several specimens of Cruziana are commonly found associated together at one sedimentary horizon, suggesting that the traces were made by populations of arthropods.[1] References edit
Further reading edit
External links edit
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