Knowledge on the Eemian (MIS 5e) fauna of Poland is based on vertebrate remains from 16 open-air localities and 8 cave sites. Considering the short period of time covered by MIS 5e, the amount of data is surprisingly large. There is still an ongoing debate on whether the age of some assemblages is Eemian, latest Saalian or even earliest Weichselian. There are faunal assemblages or stratigraphically isolated finds with some disputable evidence. The full picture of the evolution of the Eemian vertebrate fauna in the present-day territory of Poland is still far from being complete. The finds of various groups of vertebrates (fishes, amphibians, reptiles, birds and mammals) from the Eemian Interglacial of Poland are analysed in terms of their environmental preferences. A number of thermophilic species or forms which preferred temperate climate conditions are known from this period. Among them, Clethrionomys glareolus, Glis glis, Meles meles, Martes martes, Lynx lynx, Felis silvestris, Sus scrofa, Palaeoloxodon antiquus, and Stephanorhinus kirchbergensis indicate a forest environment. The presence of species that preferred more open environments ( Cricetus cricetus, Mammuthus primigenius, Coelodonta antiquitatis, and Equus ferus) is also recorded for the Eemian Interglacial of Poland. Characteristic was the presence of the large broad-toothed and flat-headed Ursus arctos taubachensis, which additionally often outnumbered remains of Ursus spelaeus sensu lato in the contemporary layers. The Eemian vertebrate fauna of Poland consisted of about 150 species (representing 61 genera and 26 families), most of which were recorded earlier from other localities of this age in central and eastern Europe.

Martes wenzensis Stach, 1959 is the only European Pliocene marten and possible ancestor of an evolutionary lineage leading through Martes vetus Kretzoi, 1942 to Martes martes Linnæus, 1758. Its occurrence ranged between c. 3.6–2.2 Ma and its presence is recorded herein from four sites: three Polish and one Bulgarian (Varshets). The oldest record from Węże 1, dated to 3.6–3.2 Ma, is also the most abundant and the type locality for this species. Only isolated teeth came from two other Polish sites, Węże 2 and Rębielice Królewskie 1A, dated to 2.5–2.2 Ma. The visceocranium from Varshets (c. 2.5 Ma) shows intermediate features between the type specimen from Węże 1 and the Early Pleistocene M. vetus, its possible descendant. The palaeontological records corroborate well with molecular data. The comparison of marten crania from Węże 1 and Varshets shows decrease in size and massiveness of teeth during the evolution of the species. Martes wenzensis shows an admixture of features inherent to M. vetus, M. martes, and M. foina Erxleben, 1777. The species resembles more M. vetus and M. martes than M. foina. It is described as a large, robust marten, with a flat forehead, short and broad viscerocranium, wide snout, robust canines, elongated and narrow premolars and enlarged carnassials.