ADVANCES
14 Scientific American, September 2019
CLAUDIA TOTIRGetty ImagesRiverside and the South Australian Museum
in Adelaide analyzed nearly 1,500 Dickinso-
nia fossils to determine whether the animals
could move on their own. “People have
speculated about [their] being mobile for a
while” because of clues in the fossil record,
Evans says, “but we wanted to examine the
lxßx³î
xDîøßxäÿxäxx³Dickinsonia to
see if we could eliminate all other possible
explanations besides mobility.”
The record includes body fossils as well
as what appear to be “trace fossils”—“foot-
prints” of sorts—that these animals left
behind, hinting they were mobile. Some
scientists suggested, however, that ancient
ocean currents may have picked the crea-
tures up and moved them. Others said the
“footprint” fossils may have actually formed
from specimens that had decayed and then
collapsed when buried in sediment.
But Evans and his team determined that
Dickinsonia indeed seem to have traveled on
their own: possibly tens of meters or more
over their lifetime. The fossil record shows
that these organisms had all moved in dif-
ferent directions; if ocean currents had
shifted them, they would have all been ori-
ented in the same direction, Evans says. The
U ̧lāD³lîßD`x
̧ää§äD§ä ̧ßxþxD§äÇx``
pathways left by Dickinsonia. If these were
left by decayed animals, “we would expect
them to be sort of random with respect to
one another,” Evans explains. “And the fact
that we’re seeing trackways [for a single
individual] moving in a preferred direction
suggests an organism moving under its
own power and moving in a direction relat-
ed to its internal biology.”
The evidence indicates Dickinsonia fed in
̧³xäÇ ̧î ̧³îxäxD ̧ ̧ßÜä ̧ßD³``DßÇxî
and then actively sought a fresh food source,
and they probably did so on relatively short
timescales—over hours or days. Some sci-
entists have hypothesized that these animals
moved by expanding and contracting their
body using muscles, and the new analy sis
supports this idea. Evans notes that al -
though scientists have found evidence for
self-directed animal movement earlier than
Dickinsonia, those animals likely were small-
er and traveled shorter distances. And, he
DlläjÙ5ääîxßäîîxÿxÜßxäxx³D³
animal move to a new location to feed.”
'îxßßxäxDß`xßääDāîxäx³l³äx§Ç
to resolve some of the debate over Dickinso-
nia and paint a clearer picture of life’s historyon Earth. “They killed all the other hypothe-
ses” about whether Dickinsonia moved or
not, says Jakob Vinther, a paleobiologist at
the University of Bristol in England, who was
not involved in the study. “This provides us
with more constraints to understand what
[these fossils] tell us about the earliest ani-
mals and animal evolution.” Paleontologist
and mathematician Renee Hoekzema of the
University of Copenhagen agrees. “Against
all odds we are really starting to resolve fun-
damental questions about the nature of the
enigmatic Ediacara biota and thus gaining
insight into the evolution of complex life on
the planet,” explains Hoekzema, who also
was not involved in the study.
Although Dickinsonia did not look like
any known living things today, there are
still some parallels between modern animal
life and archaic creatures such as these.
“We’re seeing very early on the develop-
ment of complex behaviors of mobility and
lxßx³î
xxl³äîā§xäjÚþD³ääDāäÍÙ5xäx
D³D§` ̧ø³îxäÿx³lxDߧā ̧³³
the fossil record are almost as complex as
the ones we have today.” Perhaps life on
ancient Earth was not so alien after all.
— Annie SneedPHYSICS
The Perfect
Crepe
Exploring the physics behind
the delicious dessert
With a little help from computer simula-
î ̧³äD³løllā³Däjx³³xxßäDþx ³D§§ā ̧ÇîąxlîxßD
î ̧
ßxÇxD¦³Í So suggests a new study involving these paper-thin, tricky-to-make pancakes, ÿDßx ̧
îx³§§xlÿî ̧ ̧§Dîxj
cheese or jam. By simulating the behavior
of batter poured across a tilting and rotat-
ing hot surface, a pair of engineers—sepa-
rated by half the world but united in their
passion for brunch—mathematically
determined the pan-angle-and-swirl con-
ditions that give rise to ideal crepes.
The investigation was the brainchild of
Mathieu Sellier, an engineer at New Zea-
land’s University of Canterbury, who stud-
xäøläāäîxäDîäD§xä
ß ̧ß ̧ä̧Ç
D³³x§äî ̧§Dxß ̧ÿäÍxD§ä ̧äxß þxäDä
chief brunch maker in his home and had
often wondered: What’s the best way to
coat the pan thinly and evenly with batter?
In 2016 Sellier mentioned the crepe
conundrum to Edouard Boujo, an engineer
now at École Polytechnique in France,
who studies optimization. They recast the
problem in mathematical terms: How
l ̧xä ̧³x³ąxîxlxßx³`x³î`¦-
ness between a real-world pancake and
D³lxD§jø³
̧ߧāDî ̧³xÕ5xßßxäø§îäappeared in June in Physical Review Fluids.
The optimal technique the duo found—
to pour batter into the hot pan, tilt the pan
to spread it to the edge and swirl to dis-
tribute it evenly—should not come as a
surprise to expert crepe cookers. But its
implications reach beyond the kitchen.
“This is a really good way of simplifying
the problem,” says mathematician Mat-
thew Moore of the University of Oxford,
who was not involved in the study (but
admits to a weakness for savor y crepes). He
says that probing what happens at the tran-
sition between liquid and solid states can
often get complicated. Treating crepe mak-
ing as an optimization problem is a strategy
that could be useful for other tasks.
The crepe-making process is similar
to techniques for adding thin layers to
microchips and evenly applying paint to
a car—applications that the engineers
äDā` ̧ø§lUx³xî
ß ̧îxßDÇÇß ̧D`Í
“The connection is that you want to
spread your liquid in a thin, uniform lay-
er,” Sellier says. “It’s the same problem in
a lot of cases.” — Stephen Ornes