Ecology of the Eocene Lake Messel revealed by analysis of small fish coprolites and sediments from a drilling core

A research drilling project in the Eocene Messel pit, Germany, provided the opportunity to conduct an ecological analysis of the developmental history of the former Lake Messel. The analysis of samples from different horizons of the drilling core showed that small fish coprolites were quite abundant in the biogenic sediments, down to a drilling depth of 132 m. Only in the most basal layers of the biogenic “oil-shale” sediments were no coprolites found. This can be explained by the hypothesis that when these layers were deposited no fish were living in the young Lake Messel. Another peculiar feature of these lower horizons is the presence of a new type of ephippia from water fleas which strongly resembles the ephippia of extant Ctenodaphnia magna. The absence of these Cladocera in the upper horizons might be an example of top-down control in a fossil ecosystem. Detailed analysis of the contents of the fish coprolites shows that the larvae of phantom midges (Chaoboridae) were by far the most important element of the former ecosystem over the whole life span of the lake. The ecosystem of ancient Lake Messel appears to have been quite stable. Chaoborid pupae also turned out to be an important part of the food web. Chironomid midge larvae are documented for the first time. In various horizons throughout the drilling core, dinoflagellates are present in high abundance. Mammalian coprolites are rare in the core.