The last days of Homo erectus, Ars Technica

           

Skulls from central Java may come from the last surviving population ofHomo erectus, suggests a new study dating the fossil bed and the surrounding landscape. The population’s death roughly coincides with dramatic changes in the environment, which may have caused the species’ extinction long before the firstHomo sapiensreached Southeast Asia.

The “last stand” ofHomo erectus?

University of Iowa anthropologist Russell Ciochon and his colleagues dated fossils and sediment layers from a site called Ngandong in a naturally terraced valley carved out of the surrounding hills by the Solo River. In the s, archaeologists unearthed the tops of a dozenHomo erectusskulls, along with two tibiae (shin bones). These fossils seem to be different from olderHomo erectusfossils in some important ways, like much larger cranial capacity (which suggests larger brains) and higher foreheads.

“NgandongHomo erectushas the largest brain size and highest foreheads of any knownHomo erectus,” Macquarie University geochronologist Kira Westaway , a co-author of the study, told Ars. “This indicated an important evolutionary change. The timing of this change is crucial to our interpretation and understanding of our distant cousins.”

In a bid to make sense of it all, Ciochon and his colleagues used uranium-series dating on some newly excavated mammal fossils from the same layer as theHomo erectusskulls. To piece together the whole area’s geological history and see how it might relate to theHomo erectusfossils, they also used other dating methods on sediment and rocks from Ngandong and other sites in the river valley . The results suggest that the bone bed (and therefore the collection ofHomo erectusfossils) is between (******************************************************, and 117, years old.

That makes Ngandong the last-known trace ofHomo erectusin the world.

“There is always a possibility that someone will find newHomo erectusevidence that is younger and therefore that becomes the last appearance — but this is science! At present, we make an interpretation based on the evidence that we have, and this is that Ngandong represents the last appearance ofHomo erectus, “Westaway told Ars.

Of course, that does not mean these were definitely the last of their kind in the world. The fossil record is patchy and imperfect, and we haven’t actually found all of it yet. “Our work provides the age of the last-known appearance ofHomo erectus, but this does not mean that it is the age of extinction,” Ciochon told Ars. “Small groups ofHomo erectusmay have lived longer without leaving fossil evidence. We know that there are no livingHomo erectus, but it is difficult to prove when the extinction event happened. “

Close encounters of the hominin kind

The Ngandong dates also strongly suggest thatHomo erectusmay have gone extinct, at least in Indonesia, long before our species made it that far. The most adventurousHomo sapiensexplorers were probably somewhere around the Levant or the Arabian Peninsula at the time and did not make it to the islands of Southeast Asia until around 73, years ago.

On the other hand, Ciochon and his colleagues’ timing leaves plenty of room forHomo erectusto have encountered Denisovans. That would help explain why the Denisovan genome contains a tiny fraction of genetic material from a much older species (just like many modern people genomes contain fragments of Neanderthal and Denisovan DNA).

“This older species is likelyHomo erectus,” Ciochon told Ars. “There is considerable speculation about where and when the Denisovans meetHomo erectusand what the results of those interactions were. Our dates support the genetic evidence thatHomo erectuscould have interbred with the Denisovans. “

But it’s too soon to say for sure. “This is yet to be proven, but establishing a solid chronology forHomo erectusis the first step in this investigation,” Westaway told Ars. “The possibility of intermixing with Denisovans is an exciting prospect well worth exploring.”