Cruziana

Cruziana Temporal range: Cambrian - Triassic, 537–250 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Cruziana, fossil trackways of trilobites.
Trace fossil classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Trilobita
Ichnogenus:	†Cruziana d'Orbigny, 1842

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]

• Goldring, R. (1 May 2009). "The formation of the trace fossil". Geological Magazine. 122 (1): 65–72. doi:10.1017/S0016756800034099. S2CID 130340569.
• Jensen, Soren (2006). Trace Fossils from the Lower Cambrian Mickwitzia Sandstone, South-Central Sweden. Wiley. ISBN 978-82-00-37665-1.
• Vinn, O (2014). "Cruziana traces from the Late Silurian (Pridoli) carbonate shelf of Saaremaa, Estonia". Estonian Journal of Earth Sciences. 63 (2): 71–75. doi:10.3176/earth.2014.06.

• Trackways and associated burrow; Photo--(Close-up); Graphic--(trilobite and burrow, etc)
• Argentine article on Cruziana "Remarkable Cruziana beds in the Lower Ordovician of the Cordillera Oriental, NW Argentina".

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