14 | New Scientist | 30 January 2021
AMMONITES are among the most
common marine fossils from the
age of the dinosaurs, but no one
has discovered one like this before.
It was found in Germany and shows
one of the swimming marine
molluscs without its distinctive
spiral shell (pictured bottom right),
offering a rare opportunity to study
ammonite internal anatomy.
Christian Klug at the University
of Zurich, Switzerland, recognised
the shield-like structure on the left
as part of a Subplanites ammonite
jaw, but the rest was a mystery
until a colleague photographed
the specimen under ultraviolet
light to highlight subtler features.
Through comparison with other
molluscs, Klug and his colleagues
could spot an eye (the small dark
spot in the bottom-left) and the gut
(the curved pink area on the right).
All other body parts are present too,
except for the arms (Swiss Journal
of Palaeontology, doi.org/frkh). ❚PalaeontologyAN ACTIVE volcano in Ecuador
has collapsed twice in the past
250,000 years, causing vast
rock slides that reached more
than 60 kilometres away. It could
happen again, but it isn’t possible
to predict when – although there is
no reason to think it is imminent.
Sangay lies on the eastern
edge of the Andes mountains,
overlooking the western edge
of the Amazon rainforest.
“It’s a volcano that’s in the
jungle,” says Viviana Valverde of
the Geophysical Institute in Quito,
Ecuador. As a result of its remote
location, for decades it wasn’t
regarded as a major risk, but she
says that is now changing.
Since the late 1990s, it has beenknown that “the volcano has
two scars”, says Valverde. These
suggested that the eastern
mountainside had collapsed twice
within the past 250,000 years.
Valverde and her colleagues
investigated 541 rocky hummocks
to the east of Sangay, and found
that many of them contained
rocks from the volcano. These
were left behind by at least two
rock slides, known as debris
avalanches, that took place when
part of the volcano collapsed.
The debris avalanches reached
at least 60 kilometres from the
volcano’s crater – much further
than such rock slides were
thought to be able to travel from
Sangay. Several towns lie withinthe debris avalanche zone.
Most volcanoes experience
occasional flank collapses, but the
debris avalanches don’t usually
travel so far. Valverde says Sangay’s
height is key – it rises 4000 metres
above the surrounding landscape.
The earlier debris avalanche
cannot be precisely dated, but
based on the ages of the volcano’s
rocks, the team estimates ithappened between 250,000 and
100,000 years ago. The second
debris avalanche happened
around 30,000 years ago, based
on the carbon dating of a woody
branch the researchers found
buried among the rocks (Journal
of Volcanology and Geothermal
Research, doi.org/frjs).
Sangay remains highly active, so
Valverde says a third collapse and
debris avalanche is possible – but
there is no way to say when.
It is difficult enough to predict
major volcanic eruptions, but a
further complication is that the
debris avalanches may have been
partly triggered by earthquakes,
which are also hard to predict. ❚GeologyVolcanic rock slide travelled 60 kilometres
Colin BarrasSangay
volcano rises
above the
jungleUnder the bonnet
Strange fossil is the first to show an ammonite without its shell
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