(Antfer) #1
8 June 2013 | NewScientist | 9

In this section
n Deadly skin cancer reversed by immune therapy, page 12
n Time cloak deletes chunks of history, page 14
n Mind-controlled exoskeleton, page 19

environments to expand into.
“You get more insects and fruit
in an equatorial climate. They
benefited from that.”
How, then, did Africa end up
being the cradle of humanity?
If the out-of-Asia hypothesis is
correct, early monkey-like
primates must have moved from
Asia over to Africa, sometime
around 40 million years ago,
Beard says. The hypothesis must
still explain how they made the
move, crossing the vast Tethys Sea
which separated Asia and Africa.
As Jaeger puts it: “It is difficult
to imagine small mammals
surviving on a raft for two weeks
in the sun.”
However, the extreme heat of
the PETM, and the lingering
warmth over the next few million
years, could have helped, says
Thierry Smith of the Royal Belgian
Institute of Natural Sciences in
Brussels. The high temperatures
would have created lush tropical
forests that spanned continents.
Early tree-dwelling primates
could only have spread through
such forests. “A tarsier on the
ground is prey, because it cannot
walk. It’s like a crab, it’s terrible.”
However it happened, the
move would prove to be a pivotal
moment in our history.

“[Primates] underwent a real
starburst of evolution in Africa,
which eventually led to apes and
humans,” says Beard.
We can expect to hear much
more about that first colonisation
of Africa in the near future.
“Humanity’s spread out of Africa
was undoubtedly very important,
but it wouldn’t have happened if
our primate ancestors hadn’t got
into Africa in the first place,” says
Beard. “The ‘Into Africa’ story is
very big right now – and it’s only
going to get bigger.” n
Additional reporting by Michael
Marshall

Finding Archie
The fossil of Archicebus achilles is the oldest primate skeleton ever found. Analysis
so far places it in the tarsier lineage but it may yet turn out to be a human ancestor

Monkeys

Tarsiers

Lemurs
and lorises

Dinosaur extinctionPalaeocene-EoceneThermal Maximum

Archicebus achilles

?

“Lucy”
70 60 50 40 30 20 10 0
Millions of years ago

“Ida” Darwinius masillae

Homo
sapiens

Homo erectus

Homo habilis

Australopithecus

Chimpanzee

Gibbons
Orang-Utan
Gorilla

“Humanity’s spread out
of Africa wouldn’t have
happened if primates
hadn’t got into Africa first”

Since Archicebus is so old, many will
wonder if it is a “missing link” – the
species that gave rise to all primates
alive today. The answer is a confusing
mix of “yes”, “no” and “maybe”.
No Archicebus is probably not the
ultimate link in our primate family
tree. Finding that animal is remarkably
difficult, because the earliest
chapters of the primate story have
left hardly any good fossils. While
Archicebus is an exciting find, it is not
an ancestor of lemurs and lorises, as
the evolutionary tree above shows.
There may be an older, more
primitive primate out there waiting
to be discovered.
Some readers may remember a
47-million-year-old fossil unveiled

in May 2009. Nicknamed Ida, it was
touted as this missing link. Most
biologists now think it is no more
than an early member of the lemur
and loris family.
YeS Archicebus lies very close to
the junction between tarsiers and
monkeys, apes and humans. It could
be as close as we are ever likely to get
to the missing link between these
two important groups of primates.
MAYbe For now, Archicebus lies on
the tarsier side of the tree. If and
when more good fossils from this
period are found, it is possible it
might flip onto our side (see main
story). Until we can fill in more of the
picture, though, it’s a bit of a stretch
to call it one of our missing links.

tHe elusIve ‘mIssIng lInk’


p 11): the trait, it seems, may trace
all the way back to an animal very
like Archicebus.
At the moment, analysis of
Archicebus places it not on our
direct line, but with our next-door
neighbours, the tarsiers of south-
east Asia (see chart, right). “But it
is incredibly close to the junction,
and it wouldn’t take much to flip
it over to our side of the tree,”
says Beard. “I wouldn’t be totally
shocked if in future we were to
find out that Archicebus is a basal
anthropoid [the group comprising
monkeys, apes and humans].”
He has one main reason for
believing Archicebus is closer
to home than he can prove at
present. Parts of its body are eerily
similar to what we would expect
to find in our oldest ancestor. Its
ankle bone, in particular, looks
just like a monkey’s – a feature
that led the team to name the
remarkable fossil after the Greek
hero Achilles.
Jean-Jacques Jaeger of the
University of Poitiers in France
agrees that Archicebus’s mix of
tarsier and anthropoid traits
make it hard to say which group it
belongs to. It could also turn out
to have belonged to a third group
that didn’t survive, he adds.
There are no other good primate

fossils from this far back in time.
Until we can compare it with its
peers, says Beard, Archicebus’s
exact place in the tree is going
to be unclear. “We’re almost
operating in a vacuum here.”
Perhaps most significantly, the
new fossil supports the idea that
primates originally evolved in
south-east Asia, and suggests the
ancestors of all monkeys and apes
had already split off from other
primates 55 million years ago –

millions of years earlier than
textbooks suggest. “Many of us
suspected that was the case,” says
Beard. “Archicebus solidifies that
this important branching event
goes right back to the beginning
of the Eocene.”
This links the birth of our
primate line to a major spike in
global temperatures known as
the Palaeocene-Eocene Thermal
Maximum (PETM). It also puts
our point of origin squarely in
the heart of the PETM furnace:
equatorial Asia. “Primates are
probably the most tropically
adapted mammals alive today,”
says Beard. It therefore makes
sense that they originated in a
warm climate.
What’s more, south-east Asia
would have offered a refuge for
tropical species to weather the
storm of cooler times: while
Earth’s drifting tectonic plates
dragged all major continents
across the latitudes, this region
remained where it was, right on
the equator.
“There were so many ecological
niches available in those forests
[after the extinction of the
dinosaurs 65 million years ago],”
says Jaeger. Hot temperatures, he
adds, may have provided primates
and other mammals with rich

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