The Dmanisi skull, also known as Skull 5 or D4500, is one of five 'Homo erectus' skulls discovered in Dmanisi, Georgia. Described in a publication in October 2013, it is estimated to be about 1.8 million years old and is the most complete skull of a Pleistocene Homo species, and the first complete adult hominin (the group that consists of modern humans, believed extinct human species and all of our immediate ancestors) skull of that degree of antiquity.

According to researchers, the discovery "provides the first evidence that early 'Homo' comprised adult individuals with small brains but body mass, stature and limb proportions reaching the lower range limit of modern variation."

The skull has been the cause of a paleontological controversy that is still ongoing as of 2017: many hominin fossils thought to be from different species such as 'Homo rudolfensis' or 'Homo habilis' may not have been separate species at all. Rather, they may have been a single evolving lineage; it is now postulated by some scientists that they were actually both 'Homo erectus'.

This remains a source of great debate among the scientific community.

More Info: en.wikipedia.org