Liang Bua Cave is a limestone cave in Flores island, which is part of the Lesser Sunda island chain. The cave is located 14 km northwest of Ruteng, the capital of West Flores' Manggarai Regency. The cave sits at 500 m above sea level. A number of excavations have been conducted at Liang Bua Cave since 1965. Large numbers of stone artefacts and faunal remains have been recovered, but the site is best known for the discovery of the Homo floresiensis, a hominin species with anatomically primitive traits compared to modern humans and Neanderthals [2][1][3][4][5][6][7][8].

Father Theodor L. Verhoeven, a Dutch missionary and archaeologist, was the first to report and publish about stone tools that were discovered in association with Stegodon remains in central Flores, at several sites within the Soa Basis. He claimed that it was most likely the Homo erectus from Java who made the stone tools in Flores, and they may have arrived on the island around 750 kya. Palaeoanthropologists largely dismissed his claims at the time [9][10].

During archaeological excavations at the site in September 2003, Benyamin Taurus, a hired local, was excavating a 2 by 2-meter square when he discovered the first indication of a skull at a depth of 6 meters [11]. This skull was part of a nearly complete skeleton known as Liang Bua 1 or LB1. The skeleton is extremely fragile because it has not been fossilized or covered with calcium carbonate. Recovered elements include a fairly complete cranium and mandible, right leg, and left innominate. The bones of the left leg, hands, and feet are less complete, while the vertebral column, sacrum, scapulae, clavicles, and ribs are only fragments. Tooth eruption, epiphyseal union, and tooth wear reveal that it is an adult, while the pelvic anatomy strongly indicates that it is a female [1].

Brown and colleagues reported these findings in a 2004 Nature publication [1]. They proposed a new species Homo floresiensis with LB 1 as the holotype. They went on to describe LB1 as having an extremely small stature with an endocranial volume in the early australopithecine range, as well as a distinct mix of primitive and derived traits in the cranium, mandible, and postcranial skeleton. They hypothesized that the small stature is due, in part, to island dwarfism (among other factors), a phenomenon observed in other large-bodied mammals that reduced in size to adapt to limited resources in island conditions [12]. They speculated that the first hominins to arrive in the area may have had a body size similar to Homo erectus and early Homo, with subsequent dwarfing; or that an unknown small-bodied and small-brained hominin may have arrived on Flores from the Sunda Shelf [1].

Further excavations in 2004 turned up skeletal remains of eight other individuals in similar strata that the original skeletal found in 2003. Finds include arm bones belonging to LB1, a second adult mandible, and postcranial materials from other individuals. These finds further demonstrate that LB1 is not just an aberrant or pathological individual, but a representative of a long-term, morphologically unique, small-bodied population with a configuration of features unrecorded in normal or pathological Homo sapiens [3][13].

Controversy

Since its discovery and publication in 2004, Homo floresiensis has been the subject of interest and much debate within the scientific community. According to Henneberg et al. [14], LB1 is not a new species and that the skeleton is that of a developmentally abnormal human, with features similar to those of Down Syndrome, the most common developmental disorder in humans and also documented in related hominoids such as chimpanzees and orangutans [15][14].

Other researchers, suggested that the Flores individuals suffered from microcephaly [11]. However, Vanucci et al. [13] tested this hypothesis and concluded that the skeletal remains did not fall within the range for microcephalic humans and thus they unlikely suffered from the disease [13]. Many researchers disagree with these findings believing that the authors failed to account for other variables when testing for microcephaly [16]. Peter Brown, a member of the original team that discovered the first fossil, claims that the study did not consider the characteristics that led to the fossil being declared a new species in the first place [16]. Falk et al. [17], who previously performed a CT scan on LB1, conclude that it is most likely a distinct species. They believe the cracks and chips in the study’s endocast distorted its shape [11].

Dates

Previously, the Homo floresiensis-bearing deposits together with associated materials were dated to between 95 and 12 kya, with LB1 at 18 kya. It would mean that they were present long after the arrival of Homo sapiens in the area [2][3][18][19]. These dates added to the reason why other researchers believed that the hobbit was a deceased modern human [20].

However, recent stratigraphic and chronological evidence suggests that all skeletal remains assigned to Homo floresiensis date to between 100 and 60 kya, and stone artefacts reasonably attributed to them range from 190 to 50 ky in age. These considerably older dates indicate that the Homo floresiensis were in Flores well before the arrival of modern humans in the area. It is unknown whether Homo floresiensis survived after 50 kya - potentially encountering modern humans in Flores or other hominins dispersing through southeast Asia, such as Denisovans [19].

Sources

The spatio-temporal distribution of archaeological and faunal finds at Liang Bua (Flores, Indonesia) in light of the revised chronology for Homo floresiensis

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