Renewed excavations in the Rising Star cave
More remains of Homo naledi and evidence about how the bones may have entered the cave may be on the way
Our team is underground this month in the Rising Star cave system, in South Africa. Project leader Lee Berger and I, along with several other team members, are doing periodic updates from the site on Twitter and Facebook, with hashtags #Homonaledi, #LesediChamber, and #DinalediChamber.
During the month, we are doing a series of events with National Geographic’s Explorer Classroom. School classes from anywhere in the world can interact with our team underground in the Dinaledi and Lesedi Chambers. Those events are broadcast live on YouTube while they are happening, and schools can register with National Geographic for the chance at having their own questions answered during the events.
This month we have two primary excavation goals.
The Dinaledi Chamber, which we call site 101, is the original location where we excavated more than 1500 specimens of Homo naledi in 2013. Since then, we have been monitoring conditions within the chamber but not excavating, except for recovering a few additional specimens for ESR dating.
Now after four years, our team has returned to the Dinaledi Chamber. We are excavating a limited area to test hypotheses about the formation of the hominin bone deposit.
The team enters the chamber through a vertical passageway called the Chute, a narrow squeeze with a minimum width of 18 cm. Near the bottom of the Chute, some flowstones adhere to its wall, providing evidence that this passage was geologically stable since the time that Homo naledi entered the chamber.
Many people have been curious whether some other entrance to this chamber may have existed in the past. So far, geological work in the chamber has found no other passage that might have allowed hominins or their bodies to get in. There’s a lot of evidence that the chamber must have been very inaccessible when the remains of H. naledi arrived — especially the clear difference in sediment composition between Dinaledi and other nearby chambers, and the lack of evidence for any other medium or large animal remains. It appears that the hominin remains must have entered the chamber in the same way we do today, down this Chute.
But nearly all of the hominin remains so far come from a tiny area of excavation, only 0.8 square meters, at the far end of the chamber more than 10 meters from the Chute.
Possibly the deposit was formed by hominins dropping bodies into the Chute. If so, we predict that hominin remains once must have formed a debris cone immediately below the Chute. We have recovered one H. naledi tooth in this area, but we haven’t dug to investigate if there are additional remains beneath the surface here. So we are now testing this hypothesis by undertaking a limited excavation at the base of the Chute. Also, we hypothesize that this may provide the strongest chance of finding any evidence of possible artifacts, or other behavioral evidence such as remnants of charcoal.
By contrast, if we do not find hominin remains in this part of the chamber, it would suggest either that the deposit did not form as a debris cone beneath the Chute, or that erosion has removed the hominin deposit in this part of the cave. In either case, this excavation will provide data to help us understand these processes.
At the same time, we are also excavating a new area within the Lesedi Chamber, which we call site 102. Within this chamber over the last three years, our team has recovered the remains of at least three individuals of Homo naledi, including the partial skeleton we call “Neo”.
This month, our central goal in Lesedi is to recover more of the Neo skeleton. Late last year, Marina Elliott recovered a fragment of sacrum from a very narrow section of the North-South passageway within the chamber. The sacrum is the bone that makes up the back of the pelvis. We have been able to match that sacrum to Neo’s last lumbar vertebra, so we know it belongs to him.
Most of Neo so far has been recovered from a small blind tunnel that leads off the 102 North-South passageway. But two fragments of long bones were found in that passageway on the surface, and some material from the blind tunnel may have slumped into that area.
We hypothesize that additional parts of Neo’s skeleton may lie within that North-South passageway, and we are excavating to test that hypothesis. This excavation will also increase our ability to investigate the parts of the chamber that lie further to the north, including the area called the “snail fracture passage”. Some hominin material was also recovered from the surface in the snail fracture, but we can’t investigate these sediments until a the sediment hump within the North-South fracture passage has been cleared.
We are also collecting information that may help answer outstanding questions about the Lesedi deposit. One question is: How old are the Lesedi Chamber hominins? We have strong evidence that the Dinaledi Chamber hominins are between 236,000 and 335,000 years old. Neo and the other Lesedi Chamber remains look almost identical to those within the Dinaledi Chamber, and they may be the same geological age — maybe they are even members of a single small population. But aren’t willing to assume anything without direct tests. Eric Roberts from James Cook University was here last week collecting geological data, and data collection will continue with other scientific visitors later in the month.
Another question is whether the hominin bones in Lesedi can be associated with any of the bones and teeth of other animals in this chamber. We have some evidence that many of these faunal remains may be very recent — less than 10,000 years old — and they have mostly come from the surface, not the same sedimentary context as Neo and the other hominin remains. There are only a handful of faunal remains that seem like they may come from the same sedimentary context as the hominins, and we’re not yet certain if they come from the same time period. We will be collecting more information to see if the slump area may provide additional sedimentary context and additional faunal remains.
The Dinaledi Chamber is much more difficult to enter, but in some ways the Lesedi Chamber is more challenging to excavate. Where the team is working, within the North-South fracture passage, they have only a very tight space that can accommodate a single excavator. To work there, the team has created a platform using a ladder, which extends horizontally into the narrow excavation area. Once they climb into the area, each excavator has only a few inches of clearance.
Until you have pictures, it’s hard to imagine the tight dimensions and the difficulty of working in this tiny space. We can’t get any of our video camera feeds into this space, so Elen Feuerriegel did a selfie in this excavation position, helping to show just how cramped it is:
Above ground, we are testing a new generation of equipment, including communications underground via internet. We have hard Ethernet lines going down into both of the chambers, and wifi routers enabling us to use multiple internet-connected laptops and camera devices.
This setup has been great for coordinating excavation, as both chambers can talk with each other and our team on the surface. It has also given us an entirely new capacity for reaching out to the rest of the world.
So far, having internet down in the chambers has enabled us to do three live feeds from the cave system, with two Explorer Classroom sessions through National Geographic, and one Facebook Live session. We’ve already reached schools in South Africa, Germany, the U.S., and Canada, and we’ll be continuing these sessions on Thursdays this month.
In the meantime, we have other live sessions for the public planned, to keep people updated on what’s happening underground. Wednesday, September 13, we are planning a Facebook Live through the National Geographic Facebook page, and will be updating on the progress to date.
The team has been working underground now since last Monday, and spent the first few days getting up to speed, confirming plans within the chambers, and laying out excavation grids and other preliminaries.
On Friday we recovered our first hominin specimens from the Dinaledi Chamber in this excavation, and we anticipate that more fossils will be coming this week. We’re hopeful for more results from the Lesedi Chamber, but it is slow going and may take some time before we can see what is emerging from that excavation area.