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 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
^ abcdeWoolfe, K.J. (1990). "Trace fossils as paleoenvironmental indicators in the Taylor Group (Devonian) of Antarctica". Palaeogeography, Palaeoclimatology, Palaeoecology. 80 (3–4): 301–310. Bibcode:1990PPP....80..301W. doi:10.1016/0031-0182(90)90139-X.
^Donovan, S. K. (2010). "Cruziana and Rusophycus: trace fossils produced by trilobites … in some cases?". Lethaia. 43 (2): 283–284. doi:10.1111/j.1502-3931.2009.00208.x.
^Garlock, T. L.; Isaacson, P. E. (1977). "An occurrence of a Cruziana population in the Moyer Ridge Member of the Bloomsberg Formation (Late Silurian)-Snyder County, Pennsylvania". Palaeontology. 51 (2): 282–287. JSTOR1303607.
