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1999 Field Season: Day 15

July 9, 1999

There was a lot of activity by our various crews today around the basin. To begin with, the excavations at site B8-1 continued. As we dig deeper into the paleosol we are realizing that there is a lot more to this fossil site than we had thought, even yesterday. We have now uncovered more than twenty new stone tools. Most of them are flakes; that is, they are small pieces of stone that have been broken off of a larger stone, or core. One core has also been uncovered. What is exciting about this site is that the stone tools that we thought may have been associated with the bones before, are now being found in amongst the bones. We are now pretty sure that this is a site where early humans were involved in some way with the animal bones. To be sure, we will still need to look carefully at the bones for signs of cutting by the stone tools.

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Stone tools at Site B8-1.

This cluster of stone tools was found at the same level as the new fossil finds. More direct associations of fossil bone and stone tools are leading us to believe that the assemblage at this site is not the result of bones and stone being randomly deposited together by a stream. Red boxes highlight the stone tools.

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Stone tools, highlighted by red boxes, at B8-1.
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Stone tools, highlighted by red boxes, at B8-1.

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Stone tools, highlighted by red boxes, at B8-1.

Additional fossil finds include a total of seven new ribs, and several vertebrae from the back and tail. Two of the vertebrae are still articulated, or joined as they were when the animal was alive. As to the identification of the animal, we are now pretty sure that it is a rhinoceros. We knew that the animal was very large and had short legs from the size and shape of the femur. The shoulder blade seemed odd at first and didn't match that of the grass-eating rhinoceros species, which is a common fossil in the Olorgesailie Basin. It is a better match, however, with the browsing (leaf-eating) rhinoceros which wasn't previously known in our fossil record of the basin. If we had been able to find more diagnostic parts of the skeleton right away, such as the skull, or even a tooth, we would have been able to tell right away. We still hope to find these parts of the skeleton to confirm our identification.

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B8-1: before and after.

This is a view of the site as we were getting ready to plaster this partial rib, and of the stone tools and bones that we discovered underneath. Several new ribs are visible, and you can see that they spread away from each other (the highly curved portion is the end that attaches to the spine). In the center of the ribs, to the bottom of the photo you can see a stone tool core. Close associations like these are encouraging that we have discovered an original site of early human activity.

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B8-1 before excavation.
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B8-1 before excavation.

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B8-1 before excavation.

In the morning, a lift was performed at Site A11-20. We mentioned this site briefly in the beginning of our dispatches, but haven't talked about it much since. The excavation is a completion of one started last year, and is sampling the same sand level (in Member 11') as the A11-10 site that we've also mentioned before. (By the way, they are still moving overburden.) This sand layer is usually rich in stone tools and fossils, but it doesn't cover the ancient landscape continuously. Instead it is thick in some places, and thins out as it met the ancient lake shore muds. Based on the where we find stone tools, it seems that the early humans preferred the sandy areas. At site A11-20 we see the sand layer gradually disappear into typical lake shore sediments. We have noticed that the stone tools are common in the portion of the site where there the sand occurs, and that they disappear away from the sand. We believe that the early humans that inhabited the Olorgesailie Basin at the time were exploiting these sandy environments at the ancient lake shores while avoiding the muddy areas nearby.

Another team went on a survey of sites that had been discovered over the past year. Several of the sites had been discovered by Kakai ole Mindu, a local Maasai that works on our crew, and who keeps his eyes open for things eroding out of the hillsides after the rains. One fossil he came across is a horn core of an antelope. These are extremely rare finds in the Olorgesailie Formation, and since they can be diagnostic of the species of antelope (which will help with our paleoenvironmental reconstruction), we are going to excavate the site. Another site was actually discovered by a tourist, who visited the Olorgesailie Prehistoric Site Museum and decided to wander about the countryside afterward. He had a good bit of luck and found a hippopotamus femur and several ribs exposed. He also did the right thing, and did not disturb the site, and reported it to the museum for proper study. We have set up an excavation plan at this site for later this season.