**Abstract**

In the open-cast lignite mine of Neumark-Nord (Saxony-Anhalt, Germany, Eemian interglacial period) the richest fossil fallow deer material which has been found so far was collected. About 80 articulated skeletons and partial skeletons of Dama geiselana Pfeiffer, 1998 (Cervidae, Mammalia) and 20 partial skeletons of *Cervus elaphus* in perfect state of preservation were recovered, together with skeletons of Elephas antiquus, Stephanorhinus kirchbergensis and hemitoechus, *Bos primigenius*, and *Panthera leo* spelea. The extraordinary composition of the thanatocoenosis of the deer provided decisive information on the cause of death, which is presented here. The deer show the typical preservation of drowned carcasses; 75% of the deer skeletons belong to strong males, while juveniles and females are rare, and very old individuals are missing in the deer assemblage. Several disasters in different years have led to the mass occurrence of deer. The individual age determination of the juveniles, the stage of antler development, and the level of epiphyseal adhesion are explained here. They show that the majority most probably died in autumn. This information provided the crucial approach to investigate nitrifying toxic cyanobacterial blooms as a cause of death. The biochemical results obtained by absorption spectroscopy and RP-HPLC with UV-detection, published in 2002, showed that pigments, and probably toxins, characteristic of cyanobacteria are preserved in the sediment.

**Keywords:** Pleistocene, *Dama geiselana*, *Cervus elaphus*, Neumark-Nord, Eemian, skeletal morphology, mass death, individual age determination, toxic cyanobacterial bloom
