New paper: Borings from the Silurian of Sweden — possibly the oldest deep-boring bivalves

April 27th, 2019

It was a delight to be a junior member of the team that produced this recent paper:

Claussen, A.L., Munnecke, A., Wilson, M.A. and Oswald, I. 2019. The oldest deep boring bivalves? Evidence from the Silurian of Gotland (Sweden). Facies 65: 26.

This may be the first paper for me where I’ve not yet met my co-authors. They are all from the GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany. This is where our recent graduate William Harrison is a graduate student. (He is clearly having a wonderful time there!)

Our team leader was the remarkable Lene Claussen. She did a prodigious amount of working and thinking for this study, which combines many of paleontology’s most recent tools, from isotopic analysis to micro-computed tomography. The abstract give us a synopsis of the story —

Abstract: Compared to modern counterparts, bioerosion is rare in Paleozoic reefs, especially macro-bioerosion. The unique and enigmatic Silurian reefs from Gotland (Sweden), composed of bryozoans and microbial laminates, show evidence of a large amount of bioerosion. The samples contain Trypanites trace fossils, as well as a large number of undescribed macroborings. Small articulated bivalve shells are preserved in some of these macroborings, identified from thin-sections. Three-dimensional images from micro-computed tomography (microCT) reveal an additional bivalve, which is occupying a bioerosion trace. This specimen is possibly contained in a different boring that can be classified as possibly clavate-shaped. Furthermore, evidence of nestling, such as a subsequent modification of the ichnofossils, the presence of bivalves that are much smaller than the trace, or the presence of additional specimens, is missing; therefore, it is most likely that the bivalves made the borings. This is evidence for the existence of deep-boring bivalves in the Silurian.

Top image is from Figure 3: Bioerosion traces from Nors Stenbrott, boreholes with bivalve shells in thin-section; a lateral cut through a bivalve shell (sample P3); b lateral cut through a bivalve shell (sample P13B).

From Figure 6: Processed three-dimensional microCT images of different boring traces from Nors Stenbrott, Trypanites borings in blue and the unknown ichnofossil in green; a all contained boreholes from sample SNS1; b all contained boreholes from sample Z9A, boring with bivalve with arrow.

I learned a great deal from this study and my new colleagues, especially about new techniques and the surprises they can reveal. Thank you, Lene and crew.

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