Aquatic organisms as amber inclusions and examples from a modern swamp forest

Abstract

To find aquatic organisms in tree resin may seem to be highly unlikely, but the fossil record provides numerous amber-preserved limnetic arthropods (e.g., water beetles, water striders, and crustaceans) and microorganisms (e.g., bacteria, algae, ciliates, testate amoebae, and rotifers). Here we explain the frequently discussed process of embedding aquatic organisms in tree resin based on field studies in a Florida swamp forest. Different aquatic arthropods and all major groups of limnetic microorganisms were found embedded in resin that had contact with swamp water. The taphonomy of aquatic organisms differs from that of terrestrial plants and animals that get stuck on resin surfaces and are enclosed by successive resin outflows. Large and highly motile arthropods are predestined for embedding. The number of microbial inclusions is increased when tiny drops of water with aquatic organisms become enclosed in resin while it is flowing in an aquatic environment. Bacteria and fungi may grow inside the resin as long as it has not solidified and therefore become secondarily accumulated. In contact with air, even resin that had initially been flowing into water may solidify and potentially form amber.