Dental tissue proportions in fossil orangutans from mainland Asia and Indonesia

Abstract

Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past million years. While studies have documented variation in dental tissue proportions among species of Homo, little is known about variation in enamel thickness within fossil orangutans. Here we assess dental tissue proportions, including conventional enamel thickness indices, in a large sample of fossil orangutan postcanine teeth from mainland Asia and Indonesia. We find few differences between regions, except for significantly lower average enamel thickness (AET) values in Indonesian mandibular first molars. Differences between fossil and extant orangutans are more marked, with fossil Pongo showing higher AET in most postcanine teeth. These differences are significant for maxillary and mandibular first molars. Fossil orangutans show higher AET than extant Pongo due to greater enamel cap areas, which exceed increases in enamel-dentine junction length (due to geometric scaling of areas and lengths for the AET index calculation). We also find greater dentine areas in fossil orangutans, but relative enamel thickness indices do not differ between fossil and extant taxa. When changes in dental tissue proportions between fossil and extant orangutans are compared with fossil and recent Homo sapiens, Pongo appears to show isometric reduction in enamel and dentine, while crown reduction in H. sapiens appears to be due to preferential loss of dentine. Disparate selective pressures or developmental constraints may underlie these patterns. Finally, the finding of moderately thick molar enamel in fossil orangutans may represent an additional convergent dental similarity with Homo erectus, complicating attempts to distinguish these taxa in mixed Asian faunas.

Enamel thickness and enamel growth in Oreopithecus: Combining microtomographic and histological evidence

“…Similar to the pattern reported for all extant and some fossil hominids (Olejniczak et al, 2008d;Smith et al, 2011Smith et al, , 2012, the Oreopithecus specimens investigated here provide evidence for increasing maximal enamel thickness from the LM1, through the LM2, to the LM3. The lingual enamel thickness of the metaconid is nearly uniform, while there is more variation along the protoconid lingual wall.…”

Biogeographic distribution and metric dental variation of fossil and living orangutans (Pongo spp.)

“…Despite the fact that most of these Chinese materials are without specific provenance and geological horizon, microstructure studies on the internal tissues of these fossils have produced important results revealing the possible life history strategy of past orangutans (e.g. Smith et al 2011;Hu et al 2012).…”

Intra‐ and interspecific variation in macaque molar enamel thickness

“…The latitudinal distribution of macaque species was associated with AET for these six species. However, considerable variation in enamel thickness is increasingly evident within genera (Dumont, 1995;Beynon et al, 1998;Mackiewicz et al, 2010;Smith et al, 2011Smith et al, , 2012a. Additional research is needed to determine if thick enamel in temperate macaques is a response to intensified hardobject feeding, increased abrasion, and/or a broader diet with a greater range of food material properties.…”