by Meave Leakey
Equally interesting is evidence of the use of stone tools close to the age and site where A. ghari was discovered. Although no artefacts were actually found, several broken antelope long bones show percussion marks that indicated they had been smashed for the extraction of the bone marrow. Cut marks on these bones and on an antelope lower jaw clearly indicate that meat had been cut from these bones using stone flakes. This is some of the earliest evidence of stone tools, which strongly supports the suggestion that the hands of some East African late australopithecines had become more dexterous just as the hands of the young sediba had.
Even more tantalizing is the discovery of the very earliest stone tools currently known. These 3.3-million-year-old tools were found by Sonia Harmand in 2011 at Lomekwi on the west side of Lake Turkana. They are surprising for their degree of complexity. Not only would the maker of these tools have to have had significant motor skills and manual dexterity, but the tools demonstrate that their makers must have had a strong understanding of how the stone fractures because they were using a combination technique of core reduction and battering. This Lomekwian tool industry is astonishing and has pushed the earliest known tools back in time by 700,000 years.
* * *
SOME OF WHAT we now know about australopithecines and their ancestors was yet to be discovered in 1997 when I was pondering whether I should next search for the ancestors or the descendants of anamensis. After much thought, the australopithecines won the day. As a group, they show a remarkable longevity for any hominin lineage (some three million years), taken in unison from the first australopithecines at Kanapoi, 4.2 million years ago, to the most recent robust boisei at Peninj, a full three million years later. Late nonrobust forms show some new trends in their hands and possible behaviours that suggest meat consumption. And most critically at this time, our own genus Homo turns up between 2.5 million and two million years ago. Homo evolved from a completely unknown ancestor among that elusive diversity of hominin species and gained all the right adaptations to thrive in the changing conditions. Sorting that out would be my next target.
11
A Friend for Lucy?
Impatient to get to work, we had broken our cardinal rule of beginning our field season in June—after the rainy season is truly over—and we found ourselves halted at the banks of the Kalakol River on the west side of the lake. The normally dry sand river was sodden. It would take some careful negotiating for our vehicles to cross, especially for the heavily burdened expedition lorry. We camped that night on the riverbank to the sounds of an unusual and loud chorus of frogs occupied in their frenzied search for a mate before all the water was gone. The familiar surge of excitement and anticipation that accompanies the approach to a new site was even sweeter than usual. It was May 1998, and for the first time, Louise would join me as coleader of the expedition. We each had our own plans for the fieldwork.
At Kanapoi, we had found evidence of an early biped—but not of diversity at this stage of human evolution. Yet I still did not believe that the anamensis-afarensis lineage was the only species of hominins alive between 4.2 and three million years ago. It couldn’t be! A few years earlier, Michel Brunet had announced a new species of this age, A. bahrelghazali, found in Chad’s Djurab Desert. But Brunet had only discovered one specimen, and it was the front part a mandible. This was not nearly diagnostic enough to persuade cautious scientists—especially the “lumpers” who steadfastly insist on the minimum number of species possible—that this was anything other than an A. afarensis. So we bent our steps to Lomekwi on the other side of the soft sands of the Kalakol River. Lomekwi’s sediments are of the same age as A. afarensis, and I had high hopes of finding a completely different-looking creature.
During this time, the australopithecines were undeniably the most common and successful hominin line, cropping up across a wide geographical area—Ethiopia, Kenya, Tanzania, Chad, and South Africa—a clear signature of evolutionary success. But at 2.33 million years, a completely different creature suddenly appeared on the scene as evidenced by the shape of the small teeth and rounded palate of the first unambiguously Homo maxilla found by Johanson’s team in the younger beds at Hadar in Ethiopia in 1994. This upper jaw shows clear evidence of an alternative dietary strategy to that of the megadonts we saw in the last chapter as it does not have the same thick enamel and hefty chewing molars. And after two million years, Homo became more common. The antecedent to this new type of hominin could have evolved elsewhere before migrating into the Omo-Turkana Basin. A mandible dated at 2.8 million years was published in 2015 from a site called Ledi-Geraru in the Afar region of Ethiopia. This older specimen shows a mix of characters intermediate between those typical of the australopithecines and Homo. But in 1998, nothing like this had been found yet. By looking in sediments around the three million-year mark, I hoped I might find evidence of diversity within the basin at the time Lucy lived. I certainly meant to try.
We had settled on Lomekwi because of its richly fossiliferous sediments and its geologic time frame. It was not that far from Nariokotome, where Kamoya discovered the first fragments of the Turkana Boy fifteen years before. My decision to open a new field site here was based on discoveries from those earlier expeditions. When the field crew had surveyed the Lomekwi sites in the early 1980s, they found two intriguing mandibles, which coincided with the time when A. afarensis lived at Hadar. These two curious finds had remained undescribed largely because no one understood what they represented. I hoped that if I spent more time at Lomekwi, I might find clues as to what these mandibles were. For her part, Louise was studying for her PhD at the University of London and planned to survey the younger sediments represented at Lomekwi and other sites to the north. She wanted to investigate whether there was any evidence to support Elisabeth Vrba’s provocative turnover-pulse hypothesis. Vrba had predicted that there was a major change in the faunal assemblages in Eastern and Southern Africa 2.5 million years ago and that the emergence of Homo was part of this turnover event. In addition to studying the large faunal collection housed in the Nairobi National Museum, Louise needed to collect evidence of the fauna from horizons close in age to 2.5 million years ago.
Having successfully traversed the wet sands of the Kalakol River the following morning, we drove north, exploring many sand rivers to locate a suitable site for our camp. We finally settled on a campsite right on the lakeshore not far from the Kangatukuseo River and conveniently situated near the small village of Kataboi, which had a borehole installed by missionaries that produced delicious drinking water. We would also have the untold luxury of plenty of washing water from the lake, so we would have to carry only drinking water to the camp. But as soon as the lorry turned off the road to drive down the sand river to the shore, it became hopelessly stuck. We spent the afternoon and the whole of the following day unloading the lorry and ferrying the equipment and supplies to the campsite by Land Rover. We set up a lovely camp along the lakeshore, with our tents comfortably nestled among doum palms. But as the afternoon progressed, the sky turned ominous, with huge clouds piling up in impressive columns on the horizon. The waves beat against the beach and the cooling breeze became a gale. The following morning, we awakened to a vastly different scene from the picturesque camp of the previous evening. All the tents were standing in inches of water, and the store tent had been blown over and was lying upside down beside our drenched three-month supply of food! Somewhere under the tangle of canvas and guy ropes, two tethered goats bleated pitifully. Everyone was shivering with cold. Somehow Louise managed to light a small fire to supply us all with tea while we set about repairing the devastated camp. But we say a bad start means a good season.
The 1998 field season was indeed productive. Our new trainees included Justus Erus and Stephen Muge, who had first worked with us during their school holidays at Nariokotome excavating the Turkana Boy. There was certainly a little adjustment required with the injection of young new blood in a team that had worked together for decades. Nzube rather famou
sly remarked on this once when a new recruit took time off for a shoulder stiff from carrying loads of dirt from a sieve. “The new model,” he succinctly stated, “is not the same as the old one!” So perhaps the division of labour that unfolded was a natural one. Louise worked with the young team exploring the west side sites with exposures dated between three and 1.3 million years. Going quite far afield in the younger sediments that extended far to the north, they took with them a minimum of equipment each week and slept wherever they stopped for the day. Meanwhile, my generation of the field crew and I surveyed the exposures dated between four and three million years. We spent our weeks happily camped close to a waterhole in the dry sandy bed of the beautiful, shady Lomekwi River that was filled with huge acacia trees abounding with birds. Our new arrangements were significantly less luxurious than in Richard’s day: by substituting metal camp beds with bedrolls that we laid out at night on a tarpaulin and replacing a full gourmet kitchen with a trunk of canned necessities, both teams travelled remarkably light. With radios in the cars, we could communicate regularly with one another provided that we remained in a line of sight.
On weekends, we all returned to our much more luxurious and delightfully scenic base camp. We updated our records, packed the fossils for the long and bumpy journey to the museum in Nairobi, and caught up with camp chores. Our lakeshore camp provided a truly special setting, affording us the opportunity for early morning swims and spectacular walks along the beach. After working inland at Lothagam and Kanapoi, I found this a welcome change.
Having Louise with me was a joy. I once again had someone with whom to share the great excitements and trials of leading the expedition. And once again I had a pilot and the untold convenience that this brings in such remote areas. After his accident Richard had bought a Cessna 210. This model had the same six-seat configuration as the faithful 206 it replaced, but in place of a big underbelly to stow luggage, it had retractable wheels. The result was a faster trip, but the new plane carried less cargo and required a longer strip to land on. Although Louise had obtained her pilot’s license several years earlier, it took a while before she could build up her flying hours to the point where her father felt she was competent enough to use his plane. While I was working at Kanapoi, Louise had persuaded Richard’s brother Jonathan to lend her his two-seater plane, and we had several eventful flights when I needed to get to Nairobi. In 1998, while at Lomekwi, Richard finally allowed Louise to fly his plane but only if she had an experienced pilot with her. This meant that we could fly faster and with more luggage, but it also meant that the copilot had to return to Nairobi, which left us without the aircraft.
Frank Brown, who had done so much of the geology for Richard in the early days, had joined us once again to study the geology at Lomekwi. He was assisted by a young Kenyan geologist, Patrick Gathogo. Patrick had first joined us in the museum as a volunteer and had proved himself to be one of the hardest-working people in the department. Frank was so impressed with his commitment and skills in the field that the following autumn he arranged for Patrick to enroll as a student at the University of Utah. This was the beginning of a great partnership between them. Frank passed on to Patrick as much as possible of his incredible knowledge of the Turkana Basin geology—the cumulation of decades of research.
Patrick would later build on this for his graduate studies and develop a long-term study of the geology to try to piece together and integrate all the separate chronologies from different parts of the Turkana Basin. Frank and Patrick first concentrated on the Lomekwi sites, and their detailed interpretation of the geology gave us a fine resolution for the relative placement of the Lomekwi fossils. At the same time, Ian McDougall, who had given us those precious pumice dates at Lothagam, collected samples for additional dating.
The distinctive green and brown claystones of the great ancient Lonyumun Lake are visible in sediments to the south of the Lomekwi site. This is the vast lake that we saw at Lothagam with the squashed snails below the basalt and briefly in the middle of the Kanapoi sequence far to the south. Just under four million years ago, this lake retreated from Lomekwi, and the Omo River took its place as the permanent water coursing through the Omo-Turkana Basin from the Ethiopian Highlands far to the north.
The Lomekwi sediments are sandwiched between the Murua Rith Hills that run north-south slightly inland from the lake. The steep, craggy slopes of the ancient lava that makes up these hills have heavily influenced the geology of the site because of a long series of ephemeral rivers that cut down the hills in dramatic gorges and drain across Lomekwi into the lake to the east. The geological footprint left behind by these ancient rivers is a distinctive alluvial fan: tumbled rocks and boulders dumped rapidly out of fast-flowing water in a characteristic fan shape. This pattern is repeatedly overlain by a second competing system of deposition that has its source in the much larger and perennial Omo River. Deposition from this river system was much more sedate, and the fluvial deposits are characterized by a series of upward-fining layers typical of the floodplains of a slow, meandering river system like we saw in the Upper Nawata at Lothagam.
In Lomekwi, these two opposing patterns of deposition replace each other through the sequence as the course of the meandering river changed through time. We were fortunate that there are some very clear markers to help orient ourselves in this repeating sequence. There are two beds of volcanic ash that were brought downstream by the Omo River after volcanic eruptions in the Ethiopian Highlands. The bottom-most and the oldest of the two at about 3.6 million years, the Lokochot Tuff is harder to find. Far more common and impossible to miss is the Tulu Bor Tuff at 3.4 million years. This tuff layer represents a huge ashfall from a vast volcanic eruption, and the chemical signature of this eruption has been picked up in ashes as far afield as the Mediterranean, the Red Sea, and the Baringo basin. Luckily for me, most of the fossils at Lomekwi are either just above or just below the distinctive and well-dated Tulu Bor marker. Just below the Tulu Bor Tuff is an unmissable third marker known as the Burrowed Bed. This bed is packed with the burrows and tunnels formed by worms and other invertebrates that lived on the shores of a shallow lake that briefly replaced the Omo River slightly less than 3.6 million years ago.
Modern seasonal sand rivers still drain from the hills, and we frequently found ourselves well and truly stuck as a result. That first year, the rains persisted later than usual, and a fine layer of wet clay was often concealed beneath the deceptively firm-looking sand, and our vehicles often landed up to their axles in the mud. Because of the rain, there were many frogs and toads, which were probably the attraction for the inordinate number of snakes. Hardly a day went past without a snake of some kind being spotted in the camp, and on many days, we encountered at least three deadly carpet vipers.
During that 1998 field season, as well as recovering many beautifully preserved fossils of a large variety of mammals, we discovered a number of isolated hominin teeth, but, disappointingly, nothing very significant or definitive. There were indications that the isolated teeth from Lomekwi differed from those of the contemporary A. afarensis, but the evidence was tantalizingly limited. We returned to Nairobi at the end of the three months feeling that there was surely an interesting hominin to be found at Lomekwi but that we would have to work very hard to find it. And it was only a year later that we struck gold when we visited a set of new exposures that Frank Brown and Patrick Gathogo had spotted and urged us to survey.
The whole crew was reunited in one place, in preparation for leaving, when we finally got around to visiting the new exposures in the final week of the 1999 field season. At the end of a long, hot, and unrewarding morning on the second day at this site, Justus Erus asked me to look at something he had found. A few broken and weathered fragments of what appeared to be a hominin face were scattered on the rocky surface.
At last, here was a new fossil that might answer some of my questions about the diversity of hominins at the time of the early australopithecines. But it was in terrible
shape and covered in matrix, so there was no way to know how significant this might be. On the positive side, it was just beginning to erode out of the soil. Perhaps if we were lucky, more of the skull would be hidden in the ground and in better condition. I gently removed some of the soil to see if there might be more underneath, and it looked promising. But it was too late in the day to begin the delicate task of excavating such a fragile and potentially important find. I painted the bone fragments with Bedacryl before carefully replacing the soil and covering the area with a protective rock. I was worried about hyaenas: particularly after the near tragedy of the pig skull at Kanapoi and a subsequent occurrence when they seriously damaged a young elephant skull. Apparently attracted by the strong smell of the Bedacryl, hyaenas had dug up the fossils hoping to find food.
On my return early the next morning, I was appalled to find that the stone covering the spot had been moved and the ground disturbed. Had a hyaena really been able to move this stone? My heart sank as I realised that an inquisitive Turkana herdsman, who must have been watching us from a nearby hill, had come down to see what had so interested us and had curiously poked and prodded the ground with his spear. Never before had something like this happened, and I was dismayed by the damage. I grimly and painstakingly collected all the bone fragments, and the field crew carefully sieved all the surrounding soil.
I then began to excavate the remaining bone buried in the ground. I was amazed to find the rest of the skull that went with our damaged face. But this too was in very bad shape. Roots had penetrated the bone, and large cracks ran through the specimen. Added to this, the bone was fragmented into millions of little pieces that were cemented together with a hard matrix. I could tell that I had found something potentially significant, and I desperately hoped that the damage the fossil had sustained from the spear and the roots could be repaired.