Rare fossilized algae, discovered unexpectedly, fill in evolutionary
gaps

Date:
March 23, 2021
Source:
Geological Society of America
Summary:
When a geobiology graduate student trekked into the mountains
of Canada's remote Yukon territory, she was hoping to find
microscopic fossils of early life. Even with detailed field plans,
the odds of finding just the right rocks were low. Far from leaving
empty-handed, though, she hiked back out with some of the most
significant fossils for the time period.



FULL STORY ==========================================================================
When geobiology graduate student Katie Maloney trekked into the mountains
of Canada's remote Yukon territory, she was hoping to find microscopic
fossils of early life. Even with detailed field plans, the odds of
finding just the right rocks were low. Far from leaving empty-handed,
though, she hiked back out with some of the most significant fossils
for the time period.


========================================================================== Eukaryotic life (cells with a DNA-containing nucleus) evolved over two
billion years ago, with photosynthetic algae dominating the playing
field for hundreds of millions of years as oxygen accumulated in the
Earth's atmosphere.

Geobiologists think that algae evolved first in freshwater environments
on land, then moved to the oceans. But the timing of that evolutionary transition remains a mystery, in part because the fossil record from
early Earth is sparse.

Maloney's findings were published yesterday in Geology. She and her collaborators found macroscopic fossils of multiple species of algae that thrived together on the seafloor about 950 million years ago, nestled
between bacterial mounds in a shallow ocean. The discovery partly fills
in the evolutionary gap between algae and more complex life, providing
critical time constraints for eukaryotic evolution.

Although the field site was carefully chosen by Maloney's field team
leader, sedimentologist Galen Halverson, who has worked in the region
for years, the discovery was an unexpected stroke of luck.

"I was thinking, 'maybe we'll find some microfossils,'" Maloney said. The possibility of finding larger fossils didn't cross her mind. "So as we
started to find well-preserved specimens, we stopped everything and the
whole team gathered to collect more fossils. Then we started to find these
big, complex slabs with hundreds of specimens. That was really exciting!" Determining if traces like the ones Maloney found are biogenic (formed
by living organisms) is a necessary step in paleobiology. While that determination is ultimately made in the lab, a few things tipped her off
in the field. The traces were very curvy, which can be a good indicator
of life, and there were visible structures within them. The fact that
there were hundreds of them twisted together sealed the deal for her.



==========================================================================
Few people would likely have noticed the fossils that day.

"We were really lucky that Katie was there to find them because at
first glance, they don't really look like anything," Maloney's advisor,
Marc Laflamme, said. "Katie is used to looking at very weird looking
fossils, so she has a bit of an eye for saying, 'This is something worth checking out.'" Maloney and her colleagues in the field wrestled the
heavy slabs into their helicopter for safe transport back to the lab
at the University of Toronto- Mississauga. She, Laflamme, and their collaborators used microscopy and geochemical techniques to confirm
that the fossils were indeed early eukaryotes. They then mapped out
the specimens' cellular features in detail, allowing them to identify
multiple species in the community.

While Maloney and her coauthors were writing up their results, they
were confident they had found the first macroscopic specimens from
this critical time period. During the peer review process, though, they received word from a collaborator that another group in China had made a similar discovery at about the same time -- macrofossils from a similar
period. That did not dissuade them.

"What's a few hundred million years between friends?" Laflamme
laughed. "I think our fossils have more detail, which makes them easier
to interpret...

They're beautiful. They're huge, they're well detailed, there's
anatomy. Your eyes are just drawn to them." Ultimately, having two sets
of macrofossils from approximately the same time can only improve the
timeline of eukaryotic evolution, serving as critical calibration points
for DNA-based biologic dating techniques. The new fossils also push
back the time when algae were living in marine environments, indicating
that evolution had already occurred in lakes on land. But for Maloney,
an expert in sedimentology, they also raise questions about what gets
preserved in the rock record and why.

"Algae became really important early on because of their role in
oxygenation and biogeochemical cycles," Maloney said. "So why does it take
them so long to show up reliably in the fossil record? It's definitely
making us think more about animal ecosystems and whether or not we're
seeing the whole picture, or if we're missing quite a bit from a lack
of preservation." The whole project has been engaging for Maloney,
who pivoted to algae from more recent biota. "I never expected to be
fascinated by algae," she said. "But I was pleasantly surprised as I
started investigating modern algae, finding what an important role they
play in sustainability and climate change -- all these big issues that
we're dealing with today. So it's been amazing contributing to algae's
origin story." This fieldwork was carried out with permits on traditional lands of the First Nation of Na-Cho Nyak Dun with their consent.

========================================================================== Story Source: Materials provided by Geological_Society_of_America. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Katie M. Maloney, Galen P. Halverson, James D. Schiffbauer,
Shuhai Xiao,
Timothy M. Gibson, Maxwell A. Lechte, Vivien M. Cumming, Alexie E.G.

Millikin, Jack G. Murphy, Malcolm W. Wallace, David Selby,
Marc Laflamme.

New multicellular marine macroalgae from the early Tonian
ofnorthwestern Canada. Geology, 2021; DOI: 10.1130/G48508.1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210323150719.htm

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