Looking at factors that accelerate mass extinction in the fossil record
as climate changes
Finding clues to the present in what happened 372 million years ago

Date:
December 21, 2021
Source:
University of Connecticut
Summary:
The Late Devonian mass extinction (roughly 372 million years ago)
was one of five mass extinctions in Earth's history, with roughly
75% of all species disappearing over its course. It happened in
two 'pulses,' spaced about 800,000 years apart, with most of the
extinctions happening in the second pulse. However, for one group
of animals living in eastern North America, the first pulse dealt
the deadlier blow.



FULL STORY ==========================================================================
The Late Devonian mass extinction (roughly 372 million years ago) was
one of five mass extinctions in Earth's history, with roughly 75% of
all species disappearing over its course. It happened in two "pulses,"
spaced about 800,000 years apart, with most of the extinctions happening
in the second pulse.

However, for one group of animals living in eastern North America,
the first pulse dealt the deadlier blow.


========================================================================== Research out today in Scientific Reports looks at how and why this
group of animals, called brachiopods, seemed to do the opposite of
so many other species. What caused this group to hit the accelerator
toward extinction? Brachiopods are small, shelled, filter-feeding ocean dwellers that are extremely abundant and well-preserved in the fossil
record, says researcher Jaleigh Pier '18 (CLAS), now a Ph.D. student in
Earth and Atmospheric Sciences at Cornell University. These qualities
make brachiopods ideal for studying disturbances, like mass extinctions,
from the deep past.

Pier started this research as a master's student in the Department of
Ecology and Evolutionary Biology in the lab of Professor Andrew Bush,
who is a member of EEB and Geosciences. Many samples had been previously collected by others in Bush's group, including co-author and Ph.D. student Sarah Brisson (Department of Geosciences), who also helped with the identification and classification.

The specimens were collected from several sites near the border of
New York and Pennsylvania, which, in the Late Devonian, had been a
shallow sea.

For this study, Pier identified around 8,000 brachiopod specimens to
determine which species were present leading up to this first pulse,
while Brisson identified the species that were still around after
the extinction. Andrew Beard '21 Ph.D., with guidance from Professor
Michael Hren from the Department of Geosciences, performed geochemical measurements to confirm the timing of the extinction pulses and to
determine oxygen levels during the extinctions.

Bush says it was surprising to discover the first pulse was more
detrimental to the brachiopods in this area, and they wanted to understand
why. To answer this question, Pier says it is necessary to apply a
comparative approach.



==========================================================================
"We have to compare the samples before and after to get a sense of
what survives and what completely disappears and goes extinct," Bush
says. "There's selectivity: why do certain things die out and certain
things survive? We already know the result, so we have to work backwards
and see what the lines of evidence indicate about what happened to these species." Pier says there are factors that can indicate a species'
likelihood of surviving an extinction; for example, body size tends to correlate with temperature tolerance, where smaller animals are usually
better suited to warmer environments.

Though this correlation does not always hold true, Pier says larger-scale patterns are necessary lines of evidence to draw from since tissues and
DNA are not available.

Larger-scale patterns in body size, abundance, and the depth of water that
the brachiopods seemed to prefer, can all yield insights and trends. The triggers that cause this disparity between survival and extinction are
called kill mechanisms. For the Devonian, there are two primary hypotheses
as to what could have triggered such a high extinction rate.

"One of the hypotheses for causes of the Devonian extinction was sea level change and the other was climate change," Pier says. "As the environment changed, this caused widespread anoxia, meaning animals couldn't breathe,
and they die out and then the climate changed, so temperatures got cold
in the Devonian." To determine temperature tolerance, the researchers
looked at different kinds of brachiopods in the Devonian at different
latitudes and their corresponding thermal preferences. There is also
the factor of mobility: for instance, as it was getting colder, if the
animals were unable to move to warmer environments, that could be one
reason some species went extinct.

"From our data, it seems climate change was the primary factor for
the Devonian extinction in this part of New York and Pennsylvania,"
says Pier. "Temperatures were changing, and these brachiopods would
have had a hard time moving around to a better environment because
the area is geographically isolated. For our species, 70% of them were
endemic to the region and it reflects that difficulty in migrating."
These broad patterns and concepts from past extinction events can be
applied to understand similar patterns researchers are seeing today,
says Pier, where some groups fare well while others die out.

Bush says, "In a general sense, climate change is an important
aspect of extinction. In this paper we tried to get at this extra
angle of the isolated biota and how that plays in. Most of the
time in the fossil record, anything that happens within hundreds
to thousands of years, you can't really tell it apart. Even if a
mass extinction takes place over several thousand years, you might
not be able to look at the detailed temporal spatial patterns of
what happened when, but because this event was something that
happened in a couple of pulses spread out in time we were able
to look at these spatial and temporal patterns in a different way." ========================================================================== Story Source: Materials provided by University_of_Connecticut. Original
written by Elaina Hancock. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Jaleigh Q. Pier, Sarah K. Brisson, J. Andrew Beard, Michael T. Hren,
Andrew M. Bush. Accelerated mass extinction in an isolated biota
during Late Devonian climate changes. Scientific Reports, 2021;
11 (1) DOI: 10.1038/s41598-021-03510-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211221102706.htm

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