First proof of planctivory/insectivory in a fossil fish: Thaumaturus intermedius from the Eocene Lake Messel (FRG)

Huge amounts of arthropod cuticular fragments were found in the intestinal contents of 21 specimens of Thaumaturus intermedius, a teleostoid fish from the Messel oil shale. The cuticular fragments are identical to those previously described from numerous coprolites of a certain type (‘A’) in the sediment and originate from small Crustacea (Cladocera) and larvae of Diptera (Culicidae and Chaoboridae). This identifies Thaumaturus as the producer of the most common coprolite type (A) in Messel. A pelagic and insectivorous mode of life can safely be assumed for Thaumaturus because of distribution and contents of type A coprolites. Food remains identified inside of larger specimens of Thaumaturus contain only few small bones (if any), apart from huge amounts of arthropod cuticula. Two additional coprolite types (‘B’ and ‘C’) are described in detail. Type B contains exclusively small fish bone fragments and the extremely rare Type C is intermediate in containing remains of insect cuticulae as well as fish bone.