Gigantopithecus was a massive ape that eventually went extinct because of its inability to adapt to shifting food sources due to an exclusive diet and overwhelming size.

The King-Kong-esque ape Gigantopithecus went extinct 100,000 years ago because it couldn’t adapt, according to a study by researchers from the Senckenberg Center for Human Evolution and Palaeoenvironment in Tübingen and the Senckenberg Research Institute in Frankfurt
Gigantopithecus was massive. Estimates range from nearly six to nearly 10 feet tall. A wide range of possibilities for a very sparse fossil record—only a handful of teeth and mandible bones are known to exist. 
But a recent study of the enamel on some of those teeth has led to a few conclusions. 
Prof. Hervé Bocherens from the