Flexibility of diet and habitat in Pleistocene South Asian mammals: Implications for the fate of the giant fossil ape Gigantopithecus

Abstract

Determining the diet of fossil apes is essential to understand primate evolution. The giant form from Southeast Asia, Gigantopithecus blacki, may have been up to 270 kg and survived until about 100,000 years ago. It is known only from isolated teeth and a few lower jaws with reduced front teeth and enlarged molars and premolars. A large spectrum of diets has been suggested for Gigantopithecus, ranging from carnivorous or grass-feeding in open savannah to a vegetarian diet dominated by fruits or bamboo. To determine its habitat and to understand why it became extinct, we tried to evaluate its dietary niche. The carbon stable isotopic composition of tooth enamel of this taxon compared to coeval and extant mammals from Southeastern Asia show that Gigantopithecus was a forest-dweller with a generalist vegetarian diet and was not specialized on bamboos. In southern China, Gigantopithecus lived in a forested environment, as did the coeval fauna, while in Thailand, it occupied only the forested part of a mosaic landscape including significant parts of open savannah. The carbon isotopic compositions of Gigantopithecus were different from those of omnivorous and carnivorous taxa, but very similar to those of orang-utans and unlike those of the bamboo-specialist giant panda. Therefore, even when open savannah environments were present in the landscape, Gigantopithecus foraging was limited to forested habitats. The very large size of Gigantopithecus, combined with a relatively restricted dietary niche, may explain its demise during the drastic forest reduction that characterized the glacial periods in South East Asia.

Introduction

South East Asia is still populated by a diverse assemblage of mega-mammal species, although most of them are now endangered, and several species became extinct recently in this region (e.g. Chaimanee, 2007, Louys et al., 2007, Stuart, 2015). The possible causes of these extinctions are debated, including climate change, human impact and eustatic changes in sea levels (e.g. Louys et al., 2007). One crucial information that is needed to elucidate the possible impact of these factors is the range of ecological flexibility of extinct species compared to those that survived, as it is predicted that climate change will have a stronger impact on species with limited ecological flexibility, whereas species with more flexibility would be more likely to retreat into other types of habitats (e.g. Bennett et al., 2005, Alberts and Altmann, 2006, Lorenzen et al., 2011, Bocherens et al., 2014).

Among the large mammal species that suffered from dramatic reduction of their distribution area to the point of becoming endangered or even extinct are hominoid primates such as orang-utan Pongo and the giant ape Gigantopithecus (e.g. Tougard et al., 1996, Louys et al., 2007). Gigantopithecus is probably the largest ape that ever existed on Earth, with an estimated body mass of up to 270 kg (Simons and Ettel, 1970). This taxon was restricted to the Plio-Pleistocene of southern China and the northern part of South-East Asia and is a component of the so-called Stegodon-Ailuropoda mammal fauna. Since its discovery by von Koenigswald in 1935, its diet has been much debated. A large spectrum of different dietary adaptations has been suggested, ranging from carnivorous or grass-feeding in open savannah to a vegetarian diet dominated by fruits (e.g. Livingstone, 1965, Simons and Ettel, 1970, Daegling and Grine, 1994). Some studies considered bamboo as a major component of its diet (White, 1975, Ciochon et al., 1990), a view that became widespread in popular literature. However, more recent investigations of tooth microwear patterns shed doubt on the bamboo dominated diet and concluded that Gigantopithecus had a general vegetarian diet dominated by fruits, similar to that of the chimpanzee (Daegling and Grine, 1994).

One key question to understand the causes of the extinction of this large ape is the degree of ecological flexibility exhibited by this species. Carbon isotopic tracking of palaeodiets has been successfully applied to decipher food preferences of extinct African hominids (e.g. Lee-Thorp et al., 2003, Cerling et al., 2011, Cerling et al., 2013, Sponheimer et al., 2013). This approach has, in several cases, yielded unexpected results compared to the conclusions of ecomorphological or tooth microwear analyses. For instance, robust australopithecines of the genus Paranthropus proved to be more variable in their dietary preferences than expected, including either pure C₃ or pure C₄ food resources in their diet in Southern and Eastern Africa (e.g. Cerling et al., 2011). This example shows that the development of large and low-cusped postcanine dentition in hominoids does not necessarily restrains the range of dietary possibilities, which leaves open the dietary options for Gigantopithecus with similar dental adaptation as Paranthropus.

The goal of the present study is to evaluate the ecological flexibility of Asian Pleistocene apes, including Gigantopithecus and Pongo, using carbon and oxygen isotopic composition in tooth enamel of specimens ranging from ∼15 to 30° N in South-east Asia (China and Thailand), together with coeval herbivorous and carnivorous mammalian taxa and modern representatives. This isotopic tracking of diet and habitat in a large geographical and environmental range will allow us to establish which strategies were used in the face of environmental change, i.e. habitat tracking, shift of ecological niche or reduction of niche diversity.