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EXTINCT HOMININ SPECIES LIVED SIDE BY SIDE 1.5 MILLION YEARS AGO  
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Anna K. Behrensmeyer, Kevin Hatala and Purity Kiura
November 28, 2024
The Conversation
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_ These fossil footprints are the first definitive evidence ever that
two hominin species – one our likely ancestor and the other a more
distant relative – actually coexisted at the same time and place on
the muddy shoreline of Lake Turkana _

Kimolo Mulwa at the site of the first hominin footprint discovery in
1978. Deep, sand-filled depressions to his left show hippopotamus
tracks in cross section, Anna K. Behrensmeyer

 

Human footprints stir the imagination. They invite you to follow, to
guess what someone was doing and where they were going. Fossilized
footprints preserved in rock do the same – they record instants in
the lives of many different extinct organisms, back to the earliest
creatures that walked on four feet
[[link removed]], 380 million years ago.

Discoveries in eastern Africa of tracks made by hominins – our
ancient relatives – are telling paleontologists
[[link removed]]
like [[link removed]] ourselves
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about the behavior of hominin species that walked on two feet and
resembled us but were not yet human like we are today. Our new
research focuses on footprints
[[link removed]] that amazingly
record two different species of hominins walking along the same Kenyan
lakeshore at the same time, roughly 1.5 million years ago.

Studying ancient tracks like these fills in exciting pieces of the
human evolution story because they provide evidence for hominin
behavior and locomotion that scientists cannot learn from fossilized
bones.

Finding first fossilized footprints in Kenya

The first discovery of tracks of early hominins in Kenya’s Lake
Turkana region happened by chance in 1978
[[link removed]]. A team led by one of us
(Behrensmeyer) and paleoecologist Léo Laporte was exploring the
geology and fossils of the rich paleontological record of East
Turkana. We focused on documenting the animals and environments
represented in one “time slice” of widespread sediments deposited
about 1.5 million years ago.

[man squats on excavation surface, brushing with paintbrush]
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Kimolo Mulwa at the site of the first hominin footprint discovery in
1978. Deep, sand-filled depressions to his left show hippopotamus
tracks in cross section. Anna K. Behrensmeyer

We collected fossils from the surface and dug geological step trenches
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to document the sediment layers that preserved the fossils. The back
wall of one of the trenches showed deep depressions in a layer of
solidified mud that we thought might be hippo tracks. We were curious
about what they looked like from the top down – what scientists call
the “plan view” – so we decided to expose 1 square meter of the
footprint surface next to the trench.

When I returned from more fossil bone surveys, Kimolo Mulwa, one of
the expert Kenyan field assistants on the project, had carefully
excavated the top of the mudstone layer and there was a broad smile on
his face. He said, “Mutu!” – meaning “person” – and
pointed to a shallow humanlike print in among the deep hippo tracks.

[indentations on flat sediment surface]
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The excavated surface shows the hominin trackway along with footprints
of hippos, a large bird and other animals. For the photo, scientists
filled the hominin tracks and a few other footprints with dark sand so
they would stand out against the light-colored sediment. Anna K.
Behrensmeyer

I could hardly believe it, but, yes, a humanlike footprint was clearly
recognizable on the excavated surface. And there were more hominin
tracks, coming our way out of the strata. It was awe-inspiring to
realize we were connecting with a moment in the life of a hominin that
walked here 1½ million years ago.

We excavated more of the surface and eventually found seven footprints
in a line, showing that the hominin had walked eastward out of softer
mud onto a harder, likely shallower surface. At one point the
individual’s left foot had slipped into a deep hippo print and the
hominin caught itself on its right foot to avoid falling – we could
see this clearly along the trackway.

[Comparison of a fossil footprint and a modern one]
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Comparison of the best-preserved 1978 hominin track, left, with a
modern track (women’s size 7) made by Behrensmeyer on the muddy
shoreline of Lake Turkana. The white objects inside the fossil
footprint are calcified fillings of worm burrows or roots that formed
in the sediment after the track was buried. Anna K. Behrensmeyer

Even today on the shore of modern Lake Turkana, it’s easy to slip
into hippo prints, especially if the water is a bit cloudy. We joked
about being sorry our hominin track-maker didn’t fall on its hands,
or face, so we could have a record of those parts, too.

Another set of tracks

Over four decades later, in 2021, paleontologist Louise Leakey
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and her Kenyan research team were excavating hominin fossils
discovered in the same area when team member Richard Loki uncovered a
portion of another hominin trackway. Leakey invited one of us (Hatala)
and paleoanthropologist Neil Roach
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to excavate and study the new trackway, because of our experience
working on [[link removed]] other
hominin [[link removed]] footprint sites
[[link removed]].

[3D image of footprints pressed into a surface]
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A 3D image of part of the 2021 excavated surface made by
photogrammetry, which shows the tracks of two hominin species
crossing. Kevin Hatala

The team, including 10 expert Kenyan field researchers led by Cyprian
Nyete, excavated the surface and documented the tracks with
photogrammetry
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– a method for 3D imaging. This is the best way to collect track
surfaces because the sediments are not hard enough – what geologists
call lithified [[link removed]] –
to remove from the ground safely and take to a museum.

The newly discovered tracks were made approximately 1.5 million years
ago. They occur at an earlier stratigraphic level
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ones we found in 1978 and are about a hundred thousand years older,
based on dating of volcanic deposits in the East Turkana strata.

[aerial view of about a dozen people standing in a curve on a rocky
bare landscape]
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Research team members along the perimeter of the ancient footprint
trackway. Louise N. Leakey

Who was passing through?

These footprints are especially exciting because careful anatomical
and functional analysis of their shapes shows that two different kinds
of hominins made tracks on the same lakeshore, within hours to a few
days of each other, possibly even within minutes!

We know the footprints were made very close together in time because
experiments on the modern shoreline of Lake Turkana show that a muddy
surface suitable for preserving clear tracks doesn’t last long
before being destroyed by waves or cracked by exposure to the Sun.

[fossilized indentations of footprints receding into distance on
sandy-looking ground]
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A trackway of footprints scientists hypothesize were created by a
_Paranthropus boisei_ individual. Neil T. Roach

This is the first time ever that scientists have been able to say that
_Homo erectus_ and _Paranthropus boisei_ – one our likely ancestor
and the other a more distant relative – actually coexisted at the
same time and place
[[link removed]]. Along with many
different species of mammals, they were both members of the ancient
community that inhabited the Turkana Basin.

Not only that, but with the new tracks as references, our analyses
suggest that other previously described
[[link removed]] hominin tracks
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coexisted in this area of the Turkana Basin for at least 200,000
years, repeatedly leaving their footprints in the shallow lake margin
habitat.

Other animals left tracks there as well – giant storks, smaller
birds such as pelicans, antelope and zebra, hippos and elephants –
but hominin tracks are surprisingly common for a land-based species.
What were they doing, returning again and again to this habitat, when
other primates, such as baboons, apparently did not visit the
lakeshore and leave tracks there?

[silhouette of a tree with circles for about 20 hominin species,
showing their relationships]
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The track-making species _Homo erectus_ and _Paranthropus boisei_ are
on two different branches of the hominin family tree. Smithsonian
Human Origins Program, modified by author from original artwork
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These footprints provoke new thoughts and questions about our early
relatives. Were they eating plants that grew on the lakeshore? Some
paleontologists have proposed this possibility for the robust
_Paranthropus boisei_ because the chemistry of its teeth
[[link removed]] indicate a specific
herbivorous diet of grasslike and reedlike plants. The same chemical
tests [[link removed]] on teeth of _Homo
erectus_ – the ancestral species to _Homo sapiens_ – show a mixed
diet that likely included animal protein as well as plants.

The lake margin habitat offered food in the form of reeds, freshwater
bivalves, fish, birds and reptiles such as turtles and crocodiles,
though it could have been dangerous for bipedal primates 4 or 5 feet
(1.2 to 1.5 meters) tall. Even today, people living along the shore
occasionally are attacked by crocodiles, and local hippos can be
aggressive as well. So, whatever drew the hominins to the lakeshore
must have been worth some risk.

For now it’s impossible to know exactly how the two species
interacted. New clues about their behavior could be revealed with
future excavations of more trackway surfaces. But it is fascinating to
imagine these two hominin “cousins” being close neighbors for
hundreds of thousands of years.

[people carrying water buckets at a sandy construction site in open
landscape]
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Construction of the Ileret footprint site museum, with Daasanach women
carrying water for mixing concrete. National Museums of Kenya Audio
Visual

Ancient footprints you can visit

Earlier excavations of hominin trackways near a village called Ileret
[[link removed]], 25 miles (40 km) to the north of
our new site, are being developed as a museum
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a project by the National Museums of Kenya. The public, the local
Daasanach people, educational groups and tourists will be able to see
a large number of 1.5-million-year-old hominin footprints on one
excavated surface.

That layer preserves tracks of at least eight hominin individuals, and
we now believe they represent members of both _Homo erectus_ and
_Paranthropus boisei_. Among these is a subset of individuals, all
about the same adult size, who were moving in the same direction and
appear to have been traveling as a group
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The museum built over the track site is designed to prevent erosion of
the site and to protect it from seasonal rains. A community outreach
and education center associated with the museum aims to engage local
educational groups and young people in learning and teaching others
about this exceptional record of human prehistory preserved in their
backyard. The new site museum is scheduled to open in January
2025.[The Conversation]

Anna K. Behrensmeyer
[[link removed]],
Senior Research Geologist and Curator of Vertebrate Paleontology,
_Smithsonian Institution
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Kevin Hatala
[[link removed]], Associate
Professor of Biology, _Chatham University
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and Purity Kiura
[[link removed]], Chief
Research Scientist in Archaeology and Heritage, _National Museums of
Kenya
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This article is republished from The Conversation
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the original article
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* Science
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* paleotology
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* human origins
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* human evolution
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