We use experimental taphonomy of embryos and larvae to determine the mechanisms by which endogenous bacteria stabilize rather than destroy soft tissues. Here, we show that bacteria can rapidly move from one dead organism to another through the surrounding medium—donor and recipient tissue need not be touching. In most cases tissue destruction results, but in some cases the bacteria generate stabilizing biofilms on recipient tissue that preserve its shape. We isolated, cultured, and identified phylogenetically diverse bacterial strains from the endogenous microbiotas of brine shrimp larvae (Artemia sinica) and sea urchin embryos (Heliocidaris erythrogramma) that had been killed anaerobically and then incubated aerobically to allow proliferation of endogenous bacteria in the dead tissue. We found that one Artemia-derived isolate, Marinobacter sp., is a potent generator of stabilizing biofilms and that other isolates can participate in biofilm formation or cause destruction. These results show the relative frequency of stabilizing bacteria in the endogenous microbiotas of newly dead organisms. Their ease of transmission reveals the potential for generation of a shared microbiology among groups of dead organisms, a possible contributor to uniform preservation in fossil assemblages such as Neoproterozoic and Cambrian fossil embryos.