This video is supported by Wren, a website with a monthly subscription that helps fund projects to combat the climate crisis.

Click the link in the description to learn more about making a monthly contribution that supports projects like rainforest protection programs. [♪ INTRO] Roughly 66 million years ago, an asteroid hit the Earth, non-avian dinosaurs went extinct, and their fossils went on to fascinate elementary school children and the adults they turned into. But these dinosaurs weren’t the only animals to die out.

It was a mass extinction, and just one in a long line of extinction events in the fossil record. And last week in the journal PNAS, scientists may have figured out what caused a potential mass extinction over half a billion years ago. Scientists already knew that something happened roughly 550 million years ago, during the end of the Ediacaran Period.

According to the fossil record, there was a serious drop in diversity of the animals that lived around that time. And when the COVID-19 pandemic hit and shut down field research, it gave one team of scientists the chance to figure out what happened and why. They may not have been able to go into the field, but they did pull together a bunch of pre-existing research on Ediacaran fossils, and created one large database so they could look at the big picture.

That pre-existing research had already identified sets of fossils called assemblages in the late Ediacaran. The two important ones here are the White Sea assemblage from 560 to 550 million years ago; and the Nama assemblage, from 550 to about 539 million years ago. When this team looked at their new database, they identified 70 genera, or species groups, in the White Sea assemblage.

But of those 70, only 14 were found in the Nama assemblage. That’s about an 80% loss! The data are still fuzzy on exactly how quickly these animals died off, and whether it was any faster than normal extinction rates at the time.

So the team couldn’t conclude it was definitely a mass extinction. But if future research adds enough evidence, this Ediacaran extinction would be the oldest known mass extinction of animal life by a hundred million years or so. As for what caused all that death, previous research had proposed it was biotic replacement.

According to this hypothesis, animals evolved during the Nama assemblage that were way more suited for the environment, and they outcompeted the older, White Sea animals to the point of extinction. But the team’s database showed that the White Sea and Nama animals were pretty similar to one another. If it were a competition question, we’d expect to see more of a difference between the two groups.

Animals that had a leg up due to fancy new biological systems, like new ways to eat or move, would be more likely to survive into the Nama than others. The only difference between the genera that did survive and those that didn’t is that the survivors had a higher surface area to volume ratio, meaning a greater fraction of their cells are in contact with the environment around them. For Ediacarans, that environment is seawater.

These early animals got oxygen gas into their bodies by directly absorbing it from the water around them. So if an animal were shaped more like a tube than a sphere, it would have an easier time collecting the oxygen it needed to survive. And if some global disaster happened to cause oxygen levels to decrease, that animal would also be more likely to survive than its buddies because it had more surface area to gather that oxygen.

That is what this new research proposes. A major, if not mass, extinction event around 550 million years ago was caused by a drastic drop in the oxygen dissolved in the oceans. Now, the team doesn’t propose what caused the drop in oxygen, but it is consistent with the five most popular mass extinctions as being caused by what they call “catastrophic environmental perturbation.” Basically, climate change.

Which you may have heard we’re dealing with right now. And it’s resulting in a lot of species going extinct. Enough that some scientists say we’re currently experiencing another mass extinction event.

We get to see this one up close and study it while it’s happening. That’s one silver lining… But we don’t have to end on a downer, today. Sometimes going extinct doesn’t mean you’re actually extinct.

That’s kinda what happened on the California coast, where researchers found live specimens of an animal we previously knew only from fossils. But don’t get your hopes up, Megalodon lovers. It’s a clam.

And it was described last week in the journal ZooKeys. In 2018, a scientist was hunting for sea slugs on a beach near Santa Barbara when he stumbled upon two small, translucent bivalves hanging out under a boulder. They had long, white striped feet that he had never seen before.

But it was too early to claim he’d discovered a new species. He teamed up with another researcher to see if they could identify them, but since he had only taken photos of the clams in question, there wasn’t much they could do. Fortunately, he found a third living specimen a few months later.

You can only imagine how excited he must have been. After that discovery, they dove back through old ecology reports to see if anyone had ever described the animal. And someone had…all the way back in 1937.

But that report wasn’t for a living animal. It was for two fossilized clams found near Los Angeles, dated to be somewhere between 36,000 and 28,000 years old. To explain these clams’ sudden appearance, the duo thinks they aren’t native to the area.

As even smaller baby clams, they may have hitched a ride on currents from Mexico during the marine heatwaves that happened between 2014 and 2016. Combine that rare migration with their tiny size and translucent shells, and it makes sense no one had managed to spot a living specimen before. Now that we know they’re alive and well, the team is confident that more of these clams will be found in southern California and Mexico.

And if that’s the case, our investigation of these little cuties will only have just begun. Those clams are a small example of how interconnected our world is. Heatwaves might be bringing them from one country to another.

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