Message #1488

[Stacy Dohm]

Sexual Dimorphism

Simons and Ettel (1970) do go into greater detail regarding the mandibles, however, and speculate that the size differential between two of them (Mandibles I and III) reflects sexual dimorphism. The way that the teeth fall into two distinct categories was discovered by Charles Oxnard, an Australian anatomist, when he analyzed 735 Gigantopithecus teeth. All teeth from the first incisors through the third molars occurred in both groups in equal numbers (Oxnard, 1987, cited in Ciochon et al., 1990). Furthermore, the size differential is greater than that occurring in any living primate including both gorillas and orangutans. Ciochon (et al., 1990) note that in living species this usually indicates competition between males for multiple females, but go on to note Oxnard's argument that the equal numbers of males and females suggests general promiscuity free from competition. "The resultant increased proportion of females pregnant at any one time under such a system (perhaps almost all of them), together with harsh environmental conditions, including fierce predator pressure, could combine to produce small inter- or intra-sexual selection, but strong sex-role differences and therefore strong sexual dimorphism." (Oxnard, 1987, cited in Ciochon et al, 1990). This sounds good, but does not address the fact that even in species with marked sexual dimorphism and sexual competition, males and females will be born in more or less equal numbers and can reasonably be expected to leave behind equal numbers of teeth. It seems that this is an instance where complex social behaviour is difficult to determine solely from physical remains, especially remains as regrettably incomplete as those of Gigantopithecus. If there are analogies to be made with living primates exhibiting marked sexual dimorphism, equal numbers of surviving male and female teeth cannot be a factor in the analysis.

Geographical Distribution

Geographical distribution is likewise sketchy, since the majority of remains are from one site, Liucheng Cave in Liuzhou, China, though there have been other finds in Viet Nam and in China, so that we may define south east Asia as the range of Gigantopithecus blacki. A separate species of Gigantopithecus, Gigantipithecus giganteus, was found in northern India, but this specimen predates Gigantopithecus blacki by about five million years, and there is some controversy as to the exact nature of its relationship. Simons and Ettel (1970) place it as directly ancestral to Gigantopithecus blacki, while David W. Frayer (1972) argues that it is ancestral to the Australopithicines, only to be refuted by Robert S. Corrucini (1973) on the basis of multivariate analysis and so on. Physical remains for this species are even rarer than for Gigantopithecus blacki and the opportunity for speculation and statistical gamesmanship is correspondingly greater.

Locomotion

Ciochon et al., (1990) speculate that given its size Gigantopithecus blacki was a ground dwelling ape, probably a knuckle walker, though it could just as easily been a fist walker, the exact nature of its locomotion is impossible to ascertain from mandibles. Given its mass it could not have been a gibbon-like brachiator.

Diet

When considering diet, the teeth can provide us with stronger clues via analysis of opal phytoliths.

An alternative technique [to analysis of wear patterns and other conventional methods of ascertaining diet] based on the identification of opal phytoliths found bonded to the enamel surfaces of the teeth of extinct species allows for identification of the actual plant remains eaten by an animal prior to its death. Thus the vegetative dietary preferences of an extinct species no longer have to be inferred but can be demonstrated directly through the identification of phytoliths, the inorganic remains of plant cells, on the teeth of extinct species.

(Russell L. Ciochon, Dolores R. Piperno, and Robert G. Thompson, 1990)
In an analysis of 4 Gigantopithecus teeth, Ciochon et al. (2) (1990) identified 30 structures which were "indisputably phytoliths" on two of the teeth. These thirty broke down into two categories: the vegetative parts of grasses, and the fruits and seeds of dicotyledons.

Prior to the phytolith study Ciochon was pursuing a theory of massive bamboo consumption on the part of Gigantopithecus using analogy to the penchant of other megaherbivores to depend upon a single or limited number of plants. Creatures the size of Gigantopithecus would need a source which existed in abundance. The most likely candidate is bamboo. Further, the teeth seemed to point in that direction as well:

The molar teeth of Giganto are low-crowned and flat, with very thick enamel caps. The premolars are molarized: that is, they have become broad and flattened, and thus resemble molars. The canine teeth are not sharp and pointed, but are rather broad and flat, more like what one would expect premolars to be; the incisors are small, peglike, and closely packed. These observations, combined with the massive jaw morphology, make it really an inevitable conclusion that the animal was adapted to the consumption of tough fibrous foods by cutting, crushing, and grinding them.

(Ciochon et al., 1990)
Ciochon et al., (1990) then go on to compare this morphology with that of the giant panda, another bamboo eater, and infers a diet of bamboo for Gigantopithecus.

While bamboo is a grass, the phytolith analysis does not technically either confirm or deny this theory, since it is not capable of defining the type of grass the phytolith came from. What was surprising to Ciochon was the suggestion of fruit in the diet of Gigantopithecus. Ciochon et al (2) (1990) have identified the fruit as belonging to a species in the family Moraceae or a closely related family and state "Judging from the present frequency of dental phytoliths in Gigantopithecus, fruits may have constituted a significant portion of the diet," and go on to note that the high sugar content of this type of fruit may be responsible for the high incidence of cavities in Gigantopithecus teeth (11%).

The results of this study are reported in less complete and less technical terms in the book Other Origins (Ciochon et al, 1990), and in a review of that book Jeffrey H. Schwartz (1991) notes that a great deal is being drawn from the analysis of four teeth, upon only two of which were found phytoliths, with the greatest concentration on only one. Clearly a larger sample of teeth need to be similarly analyzed, but reading the report it is difficult not to share Ciochon's (et al. (2) 1990) excitement at the findings and for the employment of this technique in paleoanthropology in general.