Note: There are 3 species within the genus Gigantopithecus, but this write up will be only on G. blacki.
When:Pleistocene (~1 million to 300,000 years ago)
Where: China, India, and Vietnam.
What: Gigantopithecus blacki is the largest ape known, though it is not know by very much. The vast majority of fossil evidence we have is isolated teeth and the most complete fossil we have is a partial lower jaw. While we can glean significant information from this material, there is also much about the morphology and life habits of Gigantopithecus that is extremely difficult, if not impossible, to determine. This does not deter researchers from trying, however!
First for the conclusions that can be at least somewhat confidently drawn from the preserved material. Gigantopithecus is a primate, and within primates is an ape. Within apes its closet living relative is the orangutan, contra earlier research which thought this gigantic ape could be more closely related to the human lineage. The anatomy of its teeth show that it was predominantly, if not entirely, a plant eater, with bamboo as its major food source. It would have had to consume tremendous amounts of bamboo everyday, like the living giant panda.
While the teeth and jaw material can tell us this animal was much larger than any living ape, it is uncertain exactly how much larger. The most famous size estimate of Gigantopithecus is the largest, which puts it at almost 10 feet (3 meters) tall for the largest specimens known. However, this is all based off the dental evidence, and just because the teeth have grown very large, does not mean the rest of the animal is equally enlarged. This can be seen if the teeth of a giant panda are compared with that of other bears. The skulls can be roughly the same size, but the panda teeth are enormous, to allow it to process the bamboo that it eats. If this is taken into account for Gigantopithecus then a size estimate of only 6 feet (1.8 meters) tall on average is produced, with adult males large than this.