6 March 2021 | New Scientist | 19PUFFERFISH are the only bony
fish that can close their eyes,
and now we know how they do it.
They sink their eyeballs deep into
their sockets and then pucker the
skin surrounding the eye together,
like a camera’s aperture closing.
The findings resolve “a
great mystery hidden in the
long-known behaviour of [these]
familiar fish”, says Keisuke
Ogimoto at the ShimonosekiMarine Science Museum in Japan.
The pufferfish’s eye-closing
ability is something that Japanese
fishers and chefs have long
noticed. But scientists had never
followed up on these observations
until Ogimoto witnessed the
behaviour with his own eyes –
and fell in love with it.
“The first time I saw a pufferfish
close its eyes in my aquarium,
I was so moved by its cuteness that
I decided to investigate,” he says.
Ogimoto and his colleagues
studied two fine-patterned puffers
(Takifugu flavipterus) living in
an aquarium at the Shimonosekimuseum. The team took video and
images of the fish’s eyes as handlers
gently squirted warm seawater into
them, and collected ultrasound
recordings of eyeball movement.
The researchers found that the
skin around the fish’s eye squeezes
over the middle of the eyeball
with a sphincter-like movement,
resembling an iris constricting over
a pupil in bright light. Just before
the skin moves, the eyeball sinksinto the head to a depth of 70 per
cent of the eye’s full diameter –
among the greatest eye-sinking
depths ever recorded in an animal
(Zoology, doi. org/fw9x).
“The various aspects of this
eye-closing behaviour were
revealed one by one, and it was a
continuous surprise,” says Ogimoto.
“It’s exciting to ponder the mystery
of the evolution of this similar-but-
different eye-closing behaviour.”
Manatees – or “sea cows” – also
close their eyes radially, but as
marine mammals they probably
evolved the trait independently. ❚THE distant forerunners of
humans may have had more
in common with chimpanzees
than we thought. An analysis
of a 4.4-million-year-old hand
suggests that they swung from
branches and knuckle-walked like
living chimps do – challenging
recent thinking that our earliest
human ancestors did neither.
In popular thinking, we are
often imagined to have evolved
from a chimpanzee-like ape on
the human lineage, members of
which are known as hominins.
Many researchers now challenge
this idea – particularly in light of
fossil evidence from the early
hominin Ardipithecus ramidus
that was published in 2009.
One well-preserved individual,
nicknamed Ardi, had bones that
seemed to suggest it walked along
branches like a monkey rather
than swinging below them like a
chimp. This hinted that our last
common ancestor with chimps
also walked along branches, and
that chimps evolved to swing and
knuckle-walk after they branched
off from hominins.
Thomas C. Prang at Texas A&MUniversity and his colleagues
disagree with this idea. They took
the measurements of Ardi’s hands
reported in 2009 and compared
them with 416 measurements
from hands across 53 species of
living primates like chimpanzees,
bonobos and humans.
“The analysis of this hand,
one of the earliest hands in the
human fossil record, suggests that
it is chimpanzee-like, implying
that both humans and chimps
evolved from an ancestor that
was chimp-like,” says Prang.
They found that Ardi’s
metacarpals and phalanges – the
bones of the fingers and palms –
were similar in size to those of
living apes, with relatively large
joint and knuckle dimensions.
These adaptations are present
in existing primates that move
around forests by swinging below
branches and may have helped
Ardi to grasp onto branches,
and even knuckle-walk.
“Ardi also has elongated,
more curved finger bones, and
we see this increased elongation
and curvature in animals that
habitually hang from branches,”says Prang (Science Advances,
doi.org/fw9v).
Larger-bodied primates
tend to hang from branches
and climb trees, while smaller-
bodied primates, such as
monkeys and many lemurs, are
able to walk along the branches.
“[This study] quite
convincingly demonstrates that
the Ardipithecus hand has some
suspensory adaptations, which
I think makes more sense giventhe body size,” says Tracy Kivell
at the University of Kent, UK.
This may suggest that the last
common ancestor of chimpanzees
and humans was relatively
chimpanzee-like, before the
major evolutionary shift towards
bipedalism and hand dexterity.
Tim White at the University
of California, Berkeley, who
discovered the A. ramidus fossil
and helped describe it in 2009,
remains unconvinced.
“This is another failed
resurrection of the antiquated
notion that living chimpanzees
are good models for our
ancestors,” says White. He
says that the Ardipithecus hand,
aside from having five fingers
and the ability to grasp, wasn’t
specifically chimpanzee-like, as
he and his colleagues originally
reported in 2009.
Sergio Almécija at the American
Museum of Natural History in
New York is also largely unmoved.
“We need more Miocene [epoch]
ape fossils pre-dating the human-
chimp split to test fundamental
aspects of our last ancestor with
apes,” he says. ❚“The first time I saw a
pufferfish close its eyes
in my aquarium, I was
moved by its cuteness”Marine biology
Ardipithecus may have
swung from branches
like a chimpanzeeKarina ShahPVE/ALAMYPufferfish pull in
their eyeballs and
pucker skin to blinkChrista Lesté-LasserreHuman evolutionOur earliest human ancestors may
have swung on branches like chimps