Sometimes, fossils can contain remnants of DNA. And determining the contents of that ancient
genetic material can be incredibly useful for understanding evolution.
But ancient DNA has a shelf life. It’s a complex molecule,
and it doesn’t last forever -- though it can stick around a surprisingly long time.
The oldest known DNA dates back hundreds of thousands of years. It’s been predicted
that DNA might be able to survive more than a million years, but that’s never been confirmed.
Until now.
A study published this week in the journal Nature
reports ancient DNA from mammoth teeth dating as far back as one point two million years.
It’s the oldest DNA
ever sequenced, and it has revealed some big surprises about mammoth evolution.
Mammoths are ancient elephants, and two species -- woolly mammoths and
Columbian mammoths -- were both important during the later parts of the Ice Age.
Woolly mammoths lived in cold, high latitude regions of North America and Eurasia.
Columbian mammoths were much bigger, and lived only in North America.
But there were many other species before them,
including the species thought to be their ancestors: steppe mammoths.
In this study, the researchers examined three mammoth molars from frozen soils in Siberia.
One of the teeth comes from a very ancient woolly mammoth,
while the other two are either from steppe mammoths, or something very similar.
The three teeth range in age from seven hundred thousand to one point two million years old.
There was DNA locked up inside these teeth, though the passing of a million
years had taken a toll on its integrity. However, with some very careful methods,
the researchers were able to reconstruct significant chunks of each mammoth’s genome.
Those chunks included portions that geneticists use to trace
the descent of evolutionary lineages over time.
This is a huge technical achievement that confirms that DNA can be extracted from fossils
over one million years old -- but it also shakes up our understanding of mammoth evolution.
See, researchers had thought that there was only
one group of mammoths in Siberia one point two million years ago.
However, by comparing the DNA sequences from the two older teeth,
the researchers determined that they were different enough to be two separate lineages.
Which is to say, two related but apparently distinct groups.
According to the DNA, one of those lineages is the ancestor of woolly mammoths,
but the second is a whole other lineage of mammoths that we didn’t know about.
Even more surprisingly, that other separate group was a partial
match for Columbian mammoths, and a partial match for woolly mammoths.
This means that early woolly mammoths must have
interbred with this unknown group at some point to produce Columbian mammoths. They’re
not descended from a single ancestral species -- instead, they’re hybrids!
This research tells us that we have a lot more to learn about mammoth evolution.
But we now know that ancient DNA has the potential to help us
uncover those mysteries, even beyond a million years ago.
Speaking of finding unexpected things in frozen landscapes,
another new study in the journal Frontiers in Marine Science reports a group of animals living
in an Antarctic environment where scientists really, really didn’t expect to find them.
You probably know that Antarctica is covered in ice, but it’s also surrounded by it.
All around the frozen continent are ice shelves,
huge slabs of ice that float on the ocean’s surface.
As you might imagine, the world beneath an ice shelf is cold and dark.
So, scientists have long suspected that not much animal life could survive down
there. All they’ve found beneath ice sheets so far are a few swimming or crawling critters.
But this new study uncovered a big surprise: animals that spend their lives in one spot.
Scientists had believed that type of lifestyle was totally impossible beneath an ice sheet.
The researchers drilled holes several hundred meters through
the Filchner Ice Shelf and sent a camera down to see what was below.
On the seafloor, 1200 meters beneath the surface, they spotted a big boulder that
was covered in animal life, and all of those animals were sessile -- attached to the rock.
With the footage they got, the researchers weren’t able to identify
all of the animals they saw, but most of them seemed to be sponges or sponge-like organisms.
The researchers believe these animals are filter
feeders -- they get their food from nutrients floating in the water.
Usually, those floating nutrients drift down from ecosystems higher in the water,
thanks to photosynthesizing plankton and the animals that eat them.
But photosynthesis requires sunlight, and there’s none of that beneath the ice shelf.
The researchers estimate that any nutrients traveling on the local water currents
would need to make a journey of up to fifteen hundred kilometers
to reach this boulder from the nearest sun-lit habitat.
It’s also possible that the animals could be feeding on nutrients within the sediments
melting slowly out of the ice shelf above them, but it’s hard to know for sure.
In fact, a lot is hard to know about this boulder community.
This is the first known example of a sessile community under an ice shelf.
The researchers are hopeful that more study might help them identify the species present. They also
want to find out what these creatures are eating and how they got there in the first place.
It could be that this ecosystem is better-connected to the outside world than we
realize, or that they really are specially adapted for this dark, frigid habitat with nothing to eat.
Either way, it means there’s more to life under the ice shelves than we knew -- so
much more that we can stumble on it in places we really don’t expect!
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