Dmanisi is located in the Caucasus in the Republic of Georgia, approximately 85 kilometers (52.8 miles) from the country's capital, Tbilisi [6]. The site is buried beneath the ruins of the medieval city of Dmanisi. Therefore, it has long been a site of archaeological interest with a prominent archaeological excavation site located within the ruins of the old city [7][4]. It is situated on a promontory elevated about 80m above the confluence of the Mashavera and Pinezaouri River valleys [8]. These rivers eroded through 80-100 m basalt beginning in the early Pleistocene, leaving the site high above the rivers today [7].

Stratigraphy

The hominin and artefact-bearing deposits (up to 3 m thick) are magnetically normal and directly cover the original surface of the basalt layer (Mashavera basalt). It is dated to c.1.8±0.01 Ma and is correlated with the Olduvai subchron. The exposed sections reveal two major stratigraphic units. 

Stratum A contains the vast majority of faunal materials as well as all hominin remains. In the upper part, it is composed of pyroclastic silt and fine sand with a weak pedogenic structure and pedogenic carbonates. Stratum B, on the other hand, contains a greater number of stone artefacts but fewer fossils. It is made up of weathered volcanic silts and sands with dark grey ash in the center and prominent basal grey ash. These two layers are separated by a calcareous horizon, which has prevented further diagenetic damage and compaction in Stratum A, allowing for exception fossil preservation [8]. 

Background

The excavations of the ruins of the medieval settlement started in 1936, on the initiative of historian Ivane Javakhishvili. In 1982, archaeologists at the site discovered 3 meter (10 ft) deep pits, cut in compact sandy clay. They believed the pits were dug by medieval inhabitants for economic reasons. After cleaning them out, fossilized animal bones were discovered on the walls and bottom of the pits. The Georgian Paleobiological Institute of the Academy of Sciences was informed immediately and systematic palaeontological excavations began in 1983 but ended in 1991 on account of financial issues.  During these excavations, a large number of palaeontological materials were found, including animal fossils and archaic stone tools. Biostratigraphy determined the age of the finds to be from the Upper Pliocene to the Lower Pleistocene [9][4].

A group of specialists from the Roman-German Archaeological Museum joined the expedition in 1991. The 1991 season was very productive and yielded well-preserved remains of rhinoceros, elephants, deer, and other animals. More stone tools were also found, often together with the animal bones. On September 25, a group of young archaeologists led by Medea Nioradze and Antje Justus uncovered a hominin mandible (D211), heads of the expedition Abesalom Vekua and David Lordkipanidze went to the site the next day after receiving news of the discovery [9]. From that first hominin fossil, more hominin remains were uncovered in Dimanisi.

Hominin fossils include an adult braincase (Skull 1), a young adult (Skull 2), a juvenile (Skull 3), an aged edentulous individual (Skull 4), and a mature adult (Skull 5) [2]. Further finds include vertebrae, ribs, clavicles, humeri, a lower limb, and a partial foot [10][11].  The site also produced 10,000 stone tools. While the majority of them are flakes, some cores and choppers were also present. The stone tools found in Dmanisi are of the Oldowan tradition [12][4][7]. 

Debate on Classification

The hominin fossils have previously been described as Homo erectus with similarities to the Turkana basin hominins [13][14][15], viewed as early Homo erectus retaining primitive features [16], compared to Homo ergaster [17], and even attributed to a new species, Homo georgicus [18][19][2].

In 2013, the excavation and analysis of a fully complete hominin skull (Skull 5) dated to 1.8 million years ago [3] sparked debate in the palaeoanthropological community [20][21]. The facial features and dentition of the skull are similar to those of a Homo habilis while its braincase shares many features with the Homo erectus [22]. 

The Dmanisi people were small (c. 150 cm). Relative to body size, their brains were smaller (545-760 cm³) than those of the “classic” Homo erectus from Africa and Asia (800-1000 cm³) [10][23][24]. In this regard, they are more similar to the African Homo habilis. The Dmanisi hominins were almost modern in their body proportions and were highly efficient walkers and runners, but their brains were tiny compared to modern humans, and their arms moved in a different way [7].

Despite some anatomical variations among the Dmanisi specimens,  the Dmanisi team [3] argues that considering they were all found in the same site and the short time period there is no sufficient evidence to assign them to more than one hominin taxon. They instead attribute the differences not to taxic diversity but to within-species taxic variation within the Homo erectus lineage including significant age-related and sexual dimorphism [2]. They determine that the assemblage offers a unique opportunity to study variability within a single early Homo population. However, this is not a universally held view [3][21][21][4]. 

Schwartz et al. [21] state that neither time nor place is necessarily related to systematic identity and that because the Dmanisi fossils were possibly deposited over as many as several hundred years, there was enough time for faunal migration and/or replacement. They believe that D2600 mandible should be the holotype of a distinct species Homo georgicus, as previously suggested by Gabunia et al. in 2002 [19], together with its equally unusual counterpart D4500 (D2600/D4500 = Skull 5).  

Whether the Dmanisi hominins belong to a single or multiple taxa, or whether they were an early form of Homo erectus, Homo erectus ergaster georgicus, a distinct species called Homo georgicus, or something else is still being debated leaving their taxonomic status unclear [7][4].