The site of Ngandong yielded calvaria (skull caps) of a dozen individuals. Absolute dating of the remains was not originally possible. A 1996 study provided surprisingly young dates of 27,000 to 53,000 years old, based on two age estimating techniques (called electron spin resonance and U-series dating). The two techniques were applied to animal teeth recently collected from the same levels where the early human calvaria were excavated in the 1930s. The reason why these dates are so surprising is that the morphology of the NG 6 and other skull caps from Ngandong is characteristic of Homo erectus. Look at the photos here, and you'll see that the crania show a low, broad braincase and pronounced supraorbital torus. These features can also be seen in the classic Homo erectus fossils of Trinil 2 and Sangiran 2. Although the Ngandong fossil sample exhibits a slightly larger cranial (braincase) capacity than earlier erectus, the skulls are clearly those of H. erectus. The age estimate implies, then, that a population of this early human species persisted well into the time period of our own species.