UNDER PRESSURE – PUSHING DOWN ON INVERTEBRATE TUBES

Tubes are among the most widespread constructions built by invertebrates, either temporarily or permanently, and may be organic, biomineralized, agglutinated, or mixed in composition. Numerous extant invertebrate groups construct such housings, and comparable forms are common in the fossil record. However, many fossil tubes display simple morphologies that hinder comparisons with modern analogs, and taphonomic processes, especially compaction, often obscure original features. A frequent alteration is compaction-induced fracturing, seen in Ediacaran and Cambrian fossils such as Corumbella. This fossil often exhibits midline structures interpreted as original features, though their potential origin as compaction fractures has received little attention. To explore this, we subjected modern sabellid annelid tubes to uniaxial compression. Weak compression was applied manually using a glass Petri dish (Escarpia and Hydroides elegans), while strong compression was performed with a mechanical press (Escarpia and Hydroides dianthus). These experiments produced fractures in both organic and biomineralized tubes, located centrally, roughly equidistant from the lateral edges, and running subparallel to them, mimicking the midlines of Corumbella. This was in addition to the cracks along the lateral borders of the tubes, which also occur in the fossils. Our results show that both the central and lateral regions of cylindrical annelid tubes are particularly prone to rupture under compression, regardless of wall composition or thickness. While these experiments do not replicate the full complexity of natural compaction within sediment, they provide valuable insight into post-collapse breakage patterns. This work supports the interpretation that some features in fossil tubes, such as the midlines in Corumbella, may result from taphonomic processes rather than original morphology. Future studies incorporating sediment-encased compaction will further refine our understanding of fossil tube deformation.