Unique Dental Morphology of Homo floresiensis and Its Evolutionary Implications

Abstract

Homo floresiensis is an extinct, diminutive hominin species discovered in the Late Pleistocene deposits of Liang Bua cave, Flores, eastern Indonesia. The nature and evolutionary origins of H. floresiensis’ unique physical characters have been intensively debated. Based on extensive comparisons using linear metric analyses, crown contour analyses, and other trait-by-trait morphological comparisons, we report here that the dental remains from multiple individuals indicate that H. floresiensis had primitive canine-premolar and advanced molar morphologies, a combination of dental traits unknown in any other hominin species. The primitive aspects are comparable to H. erectus from the Early Pleistocene, whereas some of the molar morphologies are more progressive even compared to those of modern humans. This evidence contradicts the earlier claim of an entirely modern human-like dental morphology of H. floresiensis, while at the same time does not support the hypothesis that H. floresiensis originated from a much older H. habilis or Australopithecus-like small-brained hominin species currently unknown in the Asian fossil record. These results are however consistent with the alternative hypothesis that H. floresiensis derived from an earlier Asian Homo erectus population and experienced substantial body and brain size dwarfism in an isolated insular setting. The dentition of H. floresiensis is not a simple, scaled-down version of earlier hominins.

Mosaic dental morphology in a terminal Pleistocene hominin from Dushan Cave in southern China

“…In addition, there are other traits in the postcanine dentition of Dushan 1 that are more frequently observed in H. sapiens such as the lack of transverse crests in both upper and lower premolars 30,31 or the three-rooted M 1 , a typical H. sapiens feature with higher frequencies in East Asian populations 27,32 .…”

Aspects of human physical and behavioural evolution during the last 1 million years

“…Although the claims that H. floresiensis represents a pathological form of H. sapiens are now generally disregarded, there is evidence of some developmental abnormalities in the LB1 cranium such as increased asymmetry, plagiocephaly (an unusually flattened top to the braincase), and teeth that are rotated in their sockets (Kaifu et al ., , ). Whether these are evidence that the LB1 individual was an archaic human with pathologies or a member of an isolated and inbred population with a high mutational load is still unclear.…”

Introgression, hominin dispersal and megafaunal survival in Late Pleistocene Island Southeast Asia

“…Indeed, the patterning of Denisovan ancestry across ISEA is consistent with separate Denisovan introgression events in the Philippines 18 and, potentially, in Flores 17,19 . Despite the complete lack of support for this scenario from current morphological interpretations 7,[9][10][11][20][21][22] , it is possible that pronounced dwarfism and prolonged periods of endemic island evolution for H. floresiensis and H. luzonensis complicate morphological assessments and phylogenetic placement of these groups.…”

“…A solution to this riddle would be found if H. luzonensis and/or H. floresiensis could be identified as the potential sources of the "Denisovan" contributions to modern human genomes in the region; however, this solution is not supported by current morphological interpretations. The anatomical attributes of both of these extinct ISEA hominin species are not closely identifiable with the few confirmed specimens of Denisovans from Altai and Tibet, leading paleoanthropologists to place them outside the clade comprising Denisovans, Neanderthals, and modern humans [7][8][9][10][11][20][21][22] . Moreover, morphological and archaeological data suggest that the lineages of H. floresiensis and H. luzonensis have very deep roots in the region, deeper than the estimated timescale for the emergence of the Denisovans [7][8][9][10][11][20][21][22] .…”