Stuck in the mud: experimental taphonomy and computed tomography demonstrate the critical role of sediment in stabilizing the three‐dimensional external morphology of arthropod carcasses during early fossil diagenesis.

Exceptionally preserved fossils provide critical information on the morphology and ecology of extinct organisms, but their formation requires complex pathways that affect the process of decay in any given depositional environment. The field of experimental taphonomy has produced critical insights that allow us to better understand the physical and chemical mechanisms responsible for fossil preservation. However, taphonomic experiments designed to assess the rate of morphological information loss typically require that they are performed in artificial sea water without sediment to clearly quantify any observable changes over time. Here, we use micro‐computed tomography to non‐invasively investigate changes in carcasses of the branchiopod crustacean Triops longicaudatus for over a year of post‐burial decay. After 64 weeks, specimens are still detectable as three‐dimensional carcass moulds that capture various external morphological features in life position, including the body outline, carapace, and limbs. Our results show that sediment plays a critical role in carcass stabilization in arthropods, maintaining the external integrity of the body over much longer periods of time than previously demonstrated experimentally. We hypothesize that the carcass moulds produced during decay facilitate sites for subsequent mineral precipitation needed for exceptional three‐dimensional fossilization of non‐biomineralized arthropod remains as observed in the fossil record. [ABSTRACT FROM AUTHOR]