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Researchers mapped the mammoth family tree by extracting DNA from fossils. Also, scientists found some sessile animals living under Antarctica's ice shelf, and they're really cool.

Hosted by: Hank Green

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Sources:
https://doi.org/10.1038/s41586-021-03224-9
https://www.frontiersin.org/articles/10.3389/fmars.2021.642040/full
https://press.springernature.com/million-year-old-dna-sheds-light-on-the-genomic-history-of-mammo/18802858
https://www.eurekalert.org/pub_releases/2021-02/f-sca020921.php

Image Sources:
https://commons.wikimedia.org/wiki/File:Mammuthus_trogontherii122DB.jpg
https://commons.wikimedia.org/wiki/File:Columbian_mammoth.jpg
https://commons.wikimedia.org/wiki/File:Wooly_Mammoths.jpg
https://commons.wikimedia.org/wiki/File:Mammuthus_Size_comparison.png
https://www.storyblocks.com/video/stock/dna-sequence-blue-dna-structure-with-glow-science-background-futuristic-technology-dark-blue-background-with-space-for-text-b-6dqex1ejp5f1m3h
https://www.storyblocks.com/video/stock/double-helical-structure-of-dna-strand-close-up-animation-s-xhcmjp8k8r4yuhn
https://www.storyblocks.com/video/stock/dna-strand-is-assembled-from-different-elements-3d-animation-rh61ojwa7joe97ze8
https://www.istockphoto.com/photo/woolly-mammoth-set-in-a-winter-scene-environment-16-9-panoramic-format-gm1178017061-329071329
https://www.frontiersin.org/articles/10.3389/fmars.2021.642040/full#supplementary-material
https://commons.wikimedia.org/wiki/File:Antarctic_glac-interglac_hg.png
https://www.istockphoto.com/photo/panoramic-view-of-kayaking-in-the-iceberg-graveyard-in-antarctica-gm949614238-259226492
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!  Thanks for watching this edition of SciShow News.   SciShow is brought to you by our amazing,  wonderful, fantastic community of patrons. Patrons get access to neat perks -- from  monthly Fancy Facts to our community Discord.

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