Gut microbes are the main driver of tissue decay when animals die, and were probably important for preserving soft-tissue anatomy in fossil animals.

Credit: Aodhan Butler/CC-BY 4.0

Philip Donoghue at the University of Bristol, UK, and his colleagues studied the brine shrimp (Artemia salina; pictured left) and monitored its decay (pictured, middle and right) under various conditions. They found that soon after death, the shrimp's gut wall breaks open and bacteria spill out into the body cavity. The bacteria form sticky aggregates, or biofilms, that gradually replace shrimp tissue and contain mineral deposits, as revealed by microscopy. This mineralization is a key step in tissue preservation in fossils.

Evolution of the gut led to an explosion in both animal diversity and the abundance of fossils, the authors say.

Proc. R. Soc. B 282, 20150476 (2015)