Heidelberg jaw, also called Mauer jaw, enigmatic human mandible, thought to be about 500,000 years old, found in 1907 in the great sandpit at Mauer, southeast of Heidelberg, Germany. Elephant and rhinoceros remains found in association with the fossil indicate a warm climate; the jaw has been assigned to an interglacial period of the middle Pleistocene Epoch. The chinless mandible is massive, with ascending branches almost as broad as they are high. The teeth, proportionately too small for so large a jaw, are human. The dental arch is parabolic, without spaces between the canines and first premolars, and the molars are like those of modern people but larger.
The fossil, long an isolated discovery, is difficult to classify. It was originally assigned to its own newly designated species, H. heidelbergensis, but this classification fell out of favour, and the jaw was judged to be a European example of H. erectus. More-recent discoveries, however, have shown the usefulness of postulating a species defined by traits that are shared with both the Neanderthals (H. neanderthalensis) and modern man (H. sapiens) but that are not present in H. erectus. The Heidelberg jaw has many of these features, and it is now categorized by many anthropologists as H. heidelbergensis, along with numerous specimens dating to between about 600,000 and 400,000 years ago that have been found at several African and European sites, such as Bodo (Ethiopia), Kabwe (Zambia), Petralona (Greece), and Arago (France).