''Cruziana'' is a

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

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. It first appears in upper

Fortunian The Fortunian age marks the beginning of the Phanerozoic Eon, the Paleozoic Era, and the Cambrian Period. It is the first of the two stages of the Terreneuvian series. Its base is defined as the first appearance of the trace fossil ''Treptichnus ...

rocks of northern Iran and northern Norway. ''Cruziana'' has been extensively studied because it has uses in

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...

(specific scratch patterns are unique to specific time intervals), and because the traces can reveal many aspects of their makers' behavior. ''Cruziana'' is typically associated with

trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

but can also made by other

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

. ''Cruziana'' appears in non-marine formations such as the

Beacon Supergroup The Beacon Supergroup is a geological formation exposed in Antarctica and deposited from the Devonian to the Triassic (). The unit was originally described as either a formation or sandstone, and upgraded to group and supergroup as time passed. It ...

that would have been unsuitable environments for trilobites, and in

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

sediments that were deposited after trilobites became extinct at the end of the Permian Period. ''Cruziana'' traces can reach 15 mm across and 15 cm in length, with one end usually deeper and wider than the other. The burrow may begin or end with a resting trace called ''

Rusophycus ''Rusophycus'' is a trace fossil ichnogenus allied to ''Cruziana''. ''Rusophycus'' is the resting trace, recording the outline of the tracemaker; ''Cruziana'' is made when the organism moved. The sculpture of ''Rusophycus'' may reveal the approx ...

'', the outline of which corresponds roughly to the outline of the tracemaker, 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. The ichnogenus ''

Diplichnites ''Diplichnites'' are arthropod trackways with two parallel rows of blunt to elongate, closely spaced tracks oriented approximately perpendicularly to the mid-line of the trackway. The term is more often used for the ichnofossils of this descripti ...

'' may be produced where the trackmaker sped up. Several specimens of ''Cruziana'' are commonly found associated together at one sedimentary horizon, suggesting that the traces were made by populations of arthropods.

References

External links

Trackways and associated burrowGraphic--(trilobite and burrow, etc)Argentine article on ''Cruziana''
"Remarkable ''Cruziana'' beds in the Lower Ordovician of the Cordillera Oriental, NW

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

". {{Taxonbar, from=Q5190350 Arthropod trace fossils Fossil trackways

References

Further reading

External links