Deep Endichnial Cruziana from the Lower-Middle Ordovician of Spain — A Unique Trace Fossil Record of Trilobitomorph Deep Burrowing Behavior

Abstract

Full reliefs of Cruziana furcifera from the Lower-Middle Ordovician quartzite sandstone beds (Pochico Formation, southern Spain) points to deep, infaunal burrowing of trilobites. Some specimens show an unusual vertical extension with a wider lower part and a narrower upper part in cross section. They are referred to trilobites, which burrowed deeply in the sediment and were oriented obliquely head down and tail up. Deep burrowing seems to be common for other members of the Cruziana rugosa group, foremost C. rugosa and C. furcifera, less for C. goldfussi. The deep burrowing recorded in the discussed trace fossils can be referred to the earliest common infaunalization caused by trilobites and other arthropods during the Ordovician, probably in a response to a food competition on the sea floor, which promoted a behavioral plasticity within the same taxon or closely related taxa of trilobites.

Keywords:

• Trace fossils
• Ordovician
• Cruziana
• Infaunalization
• Spain

ACKNOWLEDGMENTS

The authors would like to thank to Weronika Łaska (Institute of Geological Sciences, Jagiellonian University) for her help during latest fieldwork and for preparing some photographs of specimens. Two anonymous reviewers provided helpful remarks.

FUNDING

Research by R.-T. was supported by Project CGL2012-33281 (Secretaría de Estado de I+D+I, Spain), and Research Group RNM-178 (Junta de Andalucía). M.S. and A.U. were supported by the Jagiellonian University (DS funds). The research activity of M.R. was supported by project RYC-2009-04316 (Ramón y Cajal Program).