Small talk: a guide for recognizing and describing the influence of burrowing meiofauna in marine mudstones

Marine mud-dwelling meiofauna are both abundant and resilient. Their burrows are more likely to be preserved in cohesive mud than in granular substrates, and marine mudstones are common throughout geological time. Together, these factors suggest that meiofauna are significant contributors to the trace fossil record. However, the literature specifically addressing meiofaunal bioturbation is limited. This manuscript reviews the existing meiofaunal bioturbation literature and integrates relevant findings from adjacent research areas, including studies on cryptic bioturbation and interpretations of massive-appearing bedding. Specifically, we: (1) synthesize burrowing strategies used by common marine meiofauna and their resulting trace morphologies; (2) critically examine previously recognized meiofaunal traces within mudstones; and (3) propose best practices for describing and quantifying meiofaunal microburrows. Meiofauna use varied locomotion strategies—such as ciliary gliding, undulation, peristalsis, and complex digging—whose effectiveness depends on organism size, locomotion speed, and the mechanical properties of mud substrates ranging from viscous to elastic. These locomotion behaviours produce distinctive microburrow morphologies, usually identifiable only through petrographic or SEM analyses as subtle disruptions to sediment fabric. Due to the absence of standardized nomenclature for microburrows, we advocate morphological descriptions over assignment to existing ichnogenera.