The Middle Eocene site of Messel (GFR) is known for its complete and fully articulated fossils, embedded in bituminous claystone. This sediment was deposited in a deep lake under subtropical to tropical conditions, which favoured a proliferous growth of algae. The ensueing exhaustion of oxygen in the lake as well as the presence of poisonous volcanic gases caused the death of many swimming and flying animals entering the lake or the air above it, thus creating a thanatocoenosis. Afterwards the absence of scavengers on the lake-bottom allowed an undisturbed fossilization. Floral and faunal fossil remains include leaves (even flower petals), seeds, molluscs, insects, fishes, amphibians, reptiles, birds and mammals. Special mention is made of the many bats (e.g. Palaeochiropteryx), the leaf-eating early horse Propalaeotherium and the ant-eater Eurotamandua. The latter, along with some marsupials, birds and a crocodile, indicates a link with South America. Since this continent and Africa were separated during the Cretaceous period, this section of the Messel fauna was one of living fossils already in Middle Eocene times.