In fact, the first human fossil at Dmanisi - a mandible - was discovered in 1991. At first, excavators thought that it came from a medieval storage pit, which was under excavation since 1984, rather than from the underlying Plio-Pleistocene layers. On close examination, the mandible was identified as early human, and paleoanthropologists were drawn to the site. Recent excavations at the same site produced two early human crania. These crania, labeled D2280 and D2282, were found in the same stratigraphic level and excavation as the mandible that was recovered eight years earlier. All that remains of D2280 is the calvarium, or skullcap. D2282 is a more complete skull, consisting of a large portion of the face and calvarium, but it is missing much of the base of the skull. The D2282 cranium is smaller than D2280, which has led researchers to believe it may be from a female young adult. Both specimens are complete enough to estimate the endocranial volume. The cranial capacity is surprisingly small; the volume of each was less than 800 cc.

Although the cranial capacity of the two individuals falls in the range of early Homo, such as H. rudolfensis and H. habilis, the crania are considered significantly different from both species. This conclusion was due to the fact that both crania showed evolved features that were lacking in these two species of early Homo. The features include a supraorbital torus and upper premolar teeth having only single roots. The Dmanisi specimens share more similarities with the African species Homo ergaster than they do with the Asian Homo erectus, both of which may have existed at the time when the Dmanisi individuals lived. The only characteristic shared with H. erectus and not with H. ergaster is the presence of an angular bulge or torus at the back of the cranium. Homo ergaster specimens do not have an angular torus, whereas both D2280 and D2282 do. The presence or lack of this feature, though, is not considered significant in phylogenetic analysis. Morphological and proportional similarities that D2280 and D2282 share with H. ergaster are considered more important. These similarities have led to the classification of both cranial remains as H. ergaster. The faunal remains and stone tools also found at the site cast light on the surroundings, age, and lives of these early humans. The fauna indicates that a variety of species of late Pliocene and early Pleistocene age lived near the site. The association of the early human fossils with the fauna provides a relative date for the cranial specimens and adds credibility to the dates obtained by absolute dating techniques. The artifacts, in addition, are consistent with the types of tools that were made in Africa around 1.7 million years ago. The tools were made exclusively from local basalt, a type of volcanic rock, and consisted of choppers, scrapers, and flakes. Bifacial tools were absent from the site and most tools retained their sharp edges, indicating that the tools had not been transported by water over any great distance. These tools may well predate the beginning of the Acheulean tool industry.

The age of the site was determined with the help of absolute dating techniques, specifically isotopic dating and paleomagnetic analysis. Both potassium-argon (K-Ar) and argon (⁴⁰Ar/³⁹Ar) isotopic techniques were used to date the layer of basalt rock beneath the fossils and artifacts. These tests on the basalt gave an age of approximately 1.8-2.0 million years old. The units around the fossil layer record a change in magnetic polarity that correlates to other dated sites, most notably Olduvai Gorge in Tanzania. This change in polarity happened approximately 1.77 million years ago. Careful study of how the stratigraphic layers formed showed that these fossils were not intrusive. Instead, they were deposited as the sediment layers were forming, making the dates obtained by the different techniques applicable to the fossils and stone tools.

The fact that Dmanisi contains early human remains, lithic artifacts, and a datable geologic context is very special. The site is significant for other reasons as well. The Dmanisi finds are distinct from all other early human fossils found outside of Africa in that they have been classified as H. ergaster. This classification expands the boundaries of this species, which, until these finds, appeared to be geographically confined to East Africa. H. ergaster has been challenged by many paleoanthropologists who consider it a mere variation of the species H. erectus. The Dmanisi cranial remains show that H. ergaster is more than a limited geographical variant of another species.