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Humans belong to a large and proud lineage of animals known as bilaterians. Bilaterian because we are all bilaterally symmetrical; you can draw a line down the middle of us and each half is basically a reflection of the other.

Paleontologists have long suspected that our lineage arose more than 550 million years ago in the Ediacaran Period, just before animals of all shapes exploded in diversity during the Cambrian. But the only solid evidence they could find of these long lost ancestors were tiny horizontal tunnels preserved in fossilized sand...until now. This week, researchers publishing in the Proceedings of the National Academy of Sciences describe wormlike fossils that date back over half a billion years!

For decades, paleontologists have been intrigued by small, curved, linear grooves found in rocks that date back more than half a billion years. These suspected burrows, dubbed “Helminthoidichnites”, have been found all over the world. And many experts agree that they are evidence that tiny bilaterians wiggled around in the Ediacaran.

But there were other organisms living back then that aren't directly related to modern animals. And no one could find fossils of the burrow-makers themselves. Then, researchers from the University of California Riverside noticed some strange, tiny, oval-ish divots while examining some of these ancient burrow fossils.

In fact, these teeny impressions were in the same layer as the tunnels, which meant they probably existed at the same time. So, the team used special 3D laser scanners to create detailed images of the impressions. Those revealed that the divots were imprints of cylindrical creatures with tiny muscular grooves on their bodies.

Whatever made these fossils would've been one to two millimeters wide and anywhere from 2 to 7 millimeters long; a perfect fit for those mysterious burrows! And they probably had many of the same features that you, and I, and other bilaterians have today. For instance, the scans showed that one end was wider than the other, which likely means that they had a front and a back.

I know that, maybe like, having a front end and a back end might not sound that remarkable, but in the Ediacaran, it was. Plus, the researchers think they munched their way through a mat of microbes on the ocean floor, so they must have had mouths, guts, and anuses. The team decided to call these worm-like creatures Ikaria wariootia after the Indigenous Australian names for the site where the fossils were found.

And it probably pushed the origin of bilaterians back by millions of years, though the rocks examined haven't been conclusively dated. These mini worms could have even been the first bilaterians, that is, the first animals to have the full set of bilaterian traits. Though, even if they weren't, they can help paleontologists peer into the past and gain a better understanding of how we ended up with the wonderful diversity of organisms we have today.

Speaking of wonderful complexity: in a new paper published this week in Cell Reports, researchers have mapped and visualized the physical structure of the microscopic communities growing on human tongues. Here's what one of those communities looks like. The gray stuff in the middle is tongue tissue, and all those colorful spots are microbes.

Beautiful, right? Who'd have thought tongue bacteria could be so pretty. And this image isn't just stunning.

It demonstrates that we can take detailed pictures of our microbial mouth residents, which oddly enough, may help us learn about their role in protecting our hearts. It's no secret that lots of different bacteria live in people's mouths. Microbial DNA from oral swabs told scientists that decades ago.

But it wasn't clear exactly where these bacteria are. Knowing that could help researchers figure out how these microbes interact with one other and with our cells, an idea known as spatial ecology. That way, we can get a better idea of how they impact us.

So, over the past decade, the researchers have been developing an imaging technique called CLASI-FISH which lets them distinguish between similar-looking microbes when they zoom in on bacterial communities. Essentially, this technique labels microbes with fluorescent pigments by attaching those pigments to genetic material that match to the microbe's genetic molecules. For this new study, 21 volunteers scraped the tops of their tongues to provide a film of bacteria, saliva, and tongue cells, which was then preserved with ethanol or formaldehyde.

Next, it was time to add some color. Different kinds of bacteria got their own fluorescent pigments, so when the researchers shined different colors of light on them, they could see where they were. Then, they combined images of all those colors to build the beautiful maps.

Though everyone's tongue microbes were slightly different, it was clear right away that the bacterial communities had lots of structure to them. Certain bacteria tended to attach themselves directly to tongue cells, while others preferred the edges of the microbial moshpit. These patterns likely arise from differences between the various microbes' physiological needs.

And the researchers in the study think our cells might play a role in creating ideal homes for different species to encourage their growth. They noted that many of these microbes are able to strip an oxygen from a nitrate to make nitrite, a molecule that can be used to make nitric oxide. So it may be that our oral microbes help us make more nitric oxide than we'd be able to otherwise, and that, in turn, has real impacts on our health.

See, among other things, nitric oxide helps regulate blood pressure. And recent studies have found that higher activity of our oral microbes is associated with lower blood pressure. So researchers in this experiment think that our tongues may be cultivating these bacteria to improve our health.

But they'll need to study the communities and their structure more to discern all the details, like for example, how to best use this information to improve people's lives. And the team is excited to image other microbiomes, too, to better understand the mysterious workings of the microbial world. Thank you for watching this episode of SciShow News!

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Our patrons not only support us, they inspire us and help us come up with ideas for episodes with their questions, comments, both here and on our patron-only Discord channel. So thank you patrons, for being awesome. And if you want to join this community or learn more about it, you can go on over to Patreon.com/SciShow. [♪ OUTRO].