Laetoli, Ngorongoro, Tanzania
Laetoli footprints
3.66 million years (the Footprint Tuff, with a second trail found in 2015)
In 1978 a trail almost 27 metres long turned up in volcanic ash at Laetoli, about 70 prints from three walkers. The ash is 3.66 million years old. The feet were already doing something close to what yours do.
Why this is extraordinary
Laetoli is a plateau at the south edge of the Serengeti, about 1,800 metres up, with volcanoes to the east. In the 1970s, animal tracks turned up cemented in volcanic ash. In 1978 the hominin trail followed. Site G is almost 27 metres of footprints, about seventy of them, pressed into a wet ash that a later eruption sealed. Three walkers used it. The small one, G1, stayed to the left of the large one, G2, and a third walker put its feet in G2’s. The date on that ash is 3.66 million years.
Look at a single print and the foot is already a walking foot. The heel comes down, there is an arch, and the big toe sits in line with the others instead of sticking out to grip a branch. In 2015, about 150 metres south, the same surface gave fourteen more prints, two more people, same direction. One of them, S1, is the problem of size. The 2016 table puts S1’s average stature at 161 to 168 centimetres using a formula built for afarensis, and near 172 centimetres using a formula built for living humans, inside a wider band of about 163 to 184. That is bigger than the Site G walkers and bigger than many earlier estimates for the species.
The species is the open name. Australopithecus afarensis is the only hominin found in these upper beds, so the prints are usually given to it. They are older than Lucy, the skeleton from Ethiopia at about 3.2 million years that made afarensis famous, and they are not Lucy’s feet. A different reading says the prints look too human in the arch and the toe for the afarensis foot bones known from other sites, so some other biped may have crossed this ash. No second species has been named from the beds. The catch is the one every footprint has. The date is the volcano’s, on the tuff. The walker is identified by sharing the formation. If another biped was here and left no skull, the name moves and the walk does not.
Five prints found in 1976, at a place called Site A on the same ash, were long set aside as a bear walking upright. A 2021 study, after those prints were cleaned, compares them with bear, chimpanzee, and human feet and argues for a biped with a different foot and a crossing step, one foot set in front of the other. On that argument, two kinds of walker used one ash. The bear reading stays the other case. The 2021 comparison reports no claw marks, and it also reports that claw marks were missing from about a third of the bear prints in its own trial, so absent claws are part of the comparison and not a closed point. It reports no bear bones among more than 25,000 fossils it counts from these beds, assigned to 85 mammal species. Neither reading names a second skeleton.
The originals are covered again after study, because the tuff weathers. What you see in a museum is a cast. No solstice, star, or lunar alignment belongs to a trail of footprints, and none is added. Kondoa’s painted shelters are a different question, with their own room.
Why it matters
Bipedal walking, with a heel strike and a toe that is not a thumb, is on the ground here before the famous skeleton called Lucy, and before the big brain. If the prints belong to Australopithecus afarensis, that species was walking upright while some of its bones still look good for climbing. If they belong to a different biped, the ash has a walker we have not named from the skeletons.
Laetoli sits on the Eyasi plateau, at the southern edge of the Serengeti, in the Ngorongoro Conservation Area, near 1,800 metres above the sea. Animal tracks, and then hominin ones, are pressed into the Footprint Tuff, a layer of volcanic ash in the Upper Laetolil Beds. Wet ash took the prints. Later ash buried them. The date used for that tuff is 3.66 million years. Site G, found in 1978, holds the long trail. Three individuals walked the same way. The smallest, called G1, went along the left of the largest, G2. A third, G3, put its feet into G2’s prints. In 2015 a second patch, Site S, about 150 metres south on the same surface, gave fourteen more prints from two further walkers, S1 and S2, going the same direction.
Photo tour
1 photograph, unedited. On a phone, swipe the row. Choose one to look closely.
- The ash itself is kept covered. The photograph is a museum cast. No openly licensed picture of the 2015 Site S trail in the ground was found.
What is still unexplained
These sit beside the consensus account, with the same visual weight. None of them is marked solved.
Location and dating
- Location
- Laetoli, Enduleni ward, Ngorongoro District, northern Tanzania, on the plateau west of the Sadiman, Lemagrut, and Oldeani volcanoes. The coordinate is the locality. Site S is about 150 metres south of Site G.
- Period label
- Current consensus — open to revision Pliocene. The Footprint Tuff is dated to 3.66 million years. That is older than the skeleton known as Lucy, about 3.2 million years, which is the comparison people reach for, and which was not found here.
- How this dating was done
- The age is on the volcanic ash, by the argon clock in the tuff, not on a bone inside a print. The association of prints and species is stratigraphy. The prints and the afarensis fossils share the Upper Laetolil Beds.
- What could change it
- A second hominin species in the same beds would reopen the name on the prints. A direct date on the ash that moved off 3.66 million years would move the walk with it.
What is actually there
- Site G, found in 1978, has about 70 prints over almost 27 metres, from three walkers.
- The smallest walked beside the largest, and a third stepped in the largest prints.
- Site S, found in 2015 about 150 metres south, has 14 prints from two more walkers on the same surface.
- S1’s stature averages 161 to 168 centimetres on an afarensis formula in the 2016 table.
- The ash is dated to 3.66 million years.
- Five Site A prints from 1976 are read as a bear walking upright, and, in a 2021 comparison, as a second biped with a crossing step.
- The prints are usually covered again after study. Museum views are casts.
Open questions
| Question | Status |
|---|---|
| Are these Australopithecus afarensis? | Open. That is the only hominin named from the beds. The foot itself has been argued to look more human than some afarensis bones. |
| How large a difference in one species is too large? | Open. S1 is well above the Site G walkers. One paper reads that as males and females. A second species is the other reading, and no second skeleton has been named here. Five 1976 prints are a further case, with a bear reading and a 2021 biped reading beside each other. |
The current narrative
Where publication stands today. It is the best-supported reading, and it is open to revision. It is not a verdict.
The current narrative — open to revision
Australopithecus afarensis, already bipedal
The prints were made by Australopithecus afarensis, the hominin of these beds, walking upright at 3.66 million years with a foot committed to the ground. Large and small individuals in the same ash are males and females of that one species.
What supports this
- Afarensis is the only hominin species recovered from the Upper Laetolil Beds, and the prints are in the Footprint Tuff of those beds.
- Heel, arch, and an aligned big toe are a walking foot, and the trail is long enough to show a gait.
- Site S walks the same surface in the same direction. The size gap fits a species that already varied a great deal, which the bones of afarensis also suggest.
What pushes back
- A print is not a bone. Sharing a formation is strong and not infallible if another biped lived here and left no skeleton yet.
- Some comparisons have found the prints more human in the arch and the toe than afarensis foot bones from elsewhere.
- The 161 to 168 centimetre average for S1, and the higher human-formula figure, strains the smaller end of the afarensis sample. “Probably males and females” is the paper’s reading, not a measurement of sex.
What would settle it
Best-supported, because the beds have one named hominin and the prints are the right age and place. It moves if a second hominin turns up in the Upper Laetolil Beds with a foot that fits the trail better.
Emerging narratives
Other published readings. Each may be right. None is adopted here unless the evidence carries it.
An emerging narrative
A different biped in the same ash
The prints record a walker with a more human foot than afarensis bones show, so they may belong to another species that shared the plateau and has not been named from a skull here.
What supports this
- Published comparisons have argued that the arch and the toe of the prints sit closer to later humans than to some afarensis feet.
- Site S makes the size range wider still. A very large walker and the small G1 prints are easier to split than to force into one body plan.
- Footprints preserve soft tissue and gait, which bones do not. A mismatch with skeletons can be real.
What pushes back
- No second hominin species has been described from these beds. An unnamed walker is a gap, not a fossil.
- Afarensis itself is already variable. The 2016 paper treats S1 as that variation, not as a new name.
- The date does not care which name wins. The walk at 3.66 million years stays.
What would settle it
A serious objection to a one-species label, and it does not erase the prints. It waits on a skeleton in the same beds whose foot matches the trail and whose skull is not afarensis.
An emerging narrative
A second walker on the 1976 prints
A 2021 comparison argues that five prints found in 1976 at Site A, on the same ash as Site G, were made by a biped with a different foot and a crossing step. On that argument two kinds of walker used one surface.
What supports this
- The comparison, after the prints were cleaned, sets them beside bear, chimpanzee, and human feet and argues they sit with hominin feet.
- It argues the crossing step and the foot proportions are not the Site G trail.
- It reports no claw marks, and no bear bones among more than 25,000 fossils from the beds, in 85 mammal species.
What pushes back
- The prints were long read as a bear walking upright, which is a published reading of the same five tracks.
- The same comparison reports claw marks absent from 31 percent of the bear prints it measured, so missing claws are not only a hominin sign in that trial.
- No second skeleton has been named from these beds. A footprint reading is not a species name.
What would settle it
The 2021 biped reading and the bear reading are both published for these five prints. This room does not choose.
An emerging narrative
A bear walking upright
One published reading is that the five Site A prints are a bear that walked upright. That is the reading they carried for decades, from the shape and from the crossing step.
What supports this
- The prints were set aside as a bear, and the crossing step was part of that reading.
- A bear’s outer toe is often the large one, which was used to make sense of a step that crosses.
- The 2021 comparison itself reports that claw marks are missing from 31 percent of bear prints, so a print without claws can still be a bear’s.
What pushes back
- The 2021 comparison argues the prints resemble hominin feet more than bear feet, and that the step is narrower than the upright bears in its trial.
- It reports no bear bones in these beds.
- The date of the ash does not choose the animal. The walk at 3.66 million years stays under either name.
What would settle it
The bear reading and the 2021 biped reading use the same five prints. This room does not drop either.
Should the current view be reevaluated?
Open to revision
The age and the bipedal gait are the part to keep. The species name is the usual one and still has a critic, because a footprint is assigned by the company it keeps. The size of S1 keeps that critic in the room.
What drives this
- A trail of about 70 prints, almost 27 metres, at 3.66 million years.
- A second trail in 2015, same surface, with a walker estimated at 161 to 168 centimetres on an afarensis formula.
- One named hominin in the beds, and a published doubt that the foot matches that hominin’s bones.
- Five 1976 prints, with a bear reading and a 2021 biped reading beside each other.
This is the museum’s own weighing of the evidence. It is not a visitor vote, and it is separate from the slider.
Weigh it yourself
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If the contested reading is right
What would follow if a reading that is not the consensus turned out to be true, and what could settle it. This explains the stakes. It does not adopt the reading.
Afarensis was fully walking at 3.66 million years
Upright walking would sit well before the big brain, and before Lucy. Climbing features in afarensis skeletons would be a leftover, or a second way of moving, not a sign that the species could not walk.
Why it is still worth a test
More of the Footprint Tuff, and foot bones from the same beds, measured against G1 and S1 rather than against skeletons from another valley.
The 1976 prints are a second biped
The ash would hold two ways of walking at 3.66 million years, and the Site G trail would not be the only foot. No skeleton yet names the second walker.
Why it is still worth a test
A foot in these beds that matches the Site A prints and is not the Site G foot.
The 1976 prints are a bear
Site A would leave the hominin trail as Site G and Site S. The ash would still be 3.66 million years, and the bear would be known here from prints rather than from bones.
Why it is still worth a test
Bear bones in the same beds, or a print with claw marks on this surface.
Sources
- New footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominins eLife, 2016
- Laetoli Footprint Trails Smithsonian Human Origins Program
- Footprint evidence of early hominin locomotor diversity at Laetoli Nature, 2021. Compares the 1976 Site A prints with bear, chimpanzee, and human feet, and argues for a second biped. The bear reading is the other case in that comparison.
Image credits
- A cast of Laetoli footprints at the Natural History Museum in Vienna. This is plaster, not the ash in Tanzania. The originals are usually reburied so the tuff does not weather away. Heels, arches, and a big toe in line with the others are what the trail is known for. . Wolfgang Sauber, CC BY-SA 4.0. Shown unedited.