18 | New Scientist | 15 June 2019PhysiologyKiller’s see-through
grin makes it deadlyDEEP-SEA fish have evolved
transparent teeth which, along
with their black bodies, make
them invisible to prey.
Dragonfish are only the size of
a pencil, but they are fearsome
predators at the top of the food
chain. Their thin, eel-like bodies
support a huge black mouth that
can swallow prey half their size.
They also have razor-sharp teeth
that are nearly transparent. MarcHunt for roots of the
oak tree heads southFOSSILS found deep in the forests
of Argentina suggest that the
family of plants that include the
oak tree may have evolved in the
southern hemisphere, not the
north as previously thought.
Fagaceae is one of the most
important families of flowering
plants. Its trees are a cornerstone
of rainforests across South-East
Asia. The extensive Fagaceae fossil
record has been found only in the
northern hemisphere before.
But a pair of 52-million-year-old
fossils discovered in Laguna del
Hunco, in Argentine Patagonia,
has led researchers to suggest
that one genus in the family,
Castanopsis, began in the south.
Since work started in Laguna
del Hunco in 1999, we have found
hundreds of leaf fossils that look
like Fagaceae members but on
their own these weren’t
considered evidence enough.Plant evolution Marine biologyTHERE is a limit to the energy we
can expend during long-term
taxing activities, from trekking to
pregnancy, and it is determined by
how much energy we can get from
eating. Even the fittest people can
only expend two and a half times as
much energy over several months
as they use when resting.
“I think this is a pretty hard limit,”
says Herman Pontzer at Duke
University in North Carolina. His
team measured total energy use by
runners in the Race Across the USA
in 2015, a 5000-kilometre race
over 140 days. They then compared
the results to those from other
energy-intensive activities including
trekking, cycling and pregnancy.
To eliminate differences due
to body size, the team divided the
total energy used by each person by
their resting energy consumption.In relatively short events such
as a marathon, total energy use
can be nearly 20 times that of
resting energy use. But in 25-hour
ultramarathons, it is around nine
times. For 10-day treks, it is around
seven. For the 23-day Tour de
France cycle race, it is five times.
The team concludes that this
curve flattens out at two and a
half times resting energy use over
periods of several hundred days
(Science Advances, doi.org/c6xd).
The demands of pregnancy are just
below this limit, which just allows
for vital maternal weight gain.
The team thinks the limit exists
because we can only get so much
energy from food. Short-term, we
can beat it by using stored reserves,
but not long-term. Michael Le Page
What is the perfect dose of exercise? See
Herman Pontzer’s article on page 34Our stomachs put a limit on
extreme human endurance
Meyers at the University of
California, San Diego, and his
colleagues used electron
microscopy to discover that the
teeth contain tiny nanocrystals
that make them see-through.
Materials are transparent
when light can pass through
them with little scattering, and
these crystals in the teeth are
so small that they don’t scatter
or reflect much light (Matter,
doi.org/gf3kz4).
Dragonfish teeth are made from
an outer enamel-like layer and an
inner layer of dentine. They are
sharper than piranha teeth and
probably as hard as a great white
shark’s, says Meyers. Their dark
skin camouflages the fish in the
inky depths, and they have a
bioluminescent lure near their
mouths to entice prey.
The transparent teeth stop the
light from the lure reflecting off
them, so their cover isn’t blown.
This means the mouth is invisible
to prey right until the moment it
is caught. Ruby Prosser ScullyHowever, suspicions were
strengthened when an
international team found
two specimens there covered
in fruits and little flower parts
of the Castanopsis genus
(Science, doi.org/c6x9).
“That was when the evidence
really became overwhelming,”
says Peter Wilf of Pennsylvania
State University. His team was
“shocked” because the nearest
Castanopsis fossils were found
8000 miles away in New Guinea.
The Argentine fossils are the
oldest in the genus by about
8 million years, and date back to
the Eocene, before Earth’s land
masses split, enabling them to
spread to modern day continents
of the north.
Mark Chase of Kew Gardens in
the UK says the research shows
Fagaceae “were in the past much
more diverse than at present,
particularly on the continents
now in the southern hemisphere,
in which they are absent today”.
Adam VaughanST
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