Ancient predatory worms have scientists rethinking the history of life on Earth
EMILY KWONG, HOST:
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Five hundred million years ago, the world was a very different place. The land was kind of boring and empty, but the ocean was full of animals - very different from the animals of today.
KARMA NANGLU: Vaguely beautiful and vaguely horrifying - if you were in, like, a submarine or using, like, a deep sea rover, for example, and you were looking at the animals there, you'd find animals that are able to eat each other, animals that have the capacity to see, interact with their environment, swim and burrow. But the kinds of animals that are there are very different in terms of the proportion - like which groups are highly successful, which groups have what kind of features - and many of them look vaguely familiar to the kind of animals you'd find in a modern ecosystem, like in the ocean, but also quite alien in some ways, with different arrangements of their limbs and their eyes and all sorts of interesting features that, you know, went extinct hundreds of millions of years ago as well.
KWONG: This is Karma Nanglu, a postdoctoral fellow at Harvard's Museum of Comparative Zoology. And he's spent a lot of time studying this period - the Cambrian period. Five hundred million years ago, there were all these different life forms. It was a total renaissance of biodiversity on Earth.
NANGLU: We have the extremely rapid, from a geological perspective, appearance of pretty much every major animal group you can imagine in the fossil record for the first time.
KWONG: Basically, the ancient ocean was full of our animal ancestors, and Karma has devoted his career to studying them. As far as he's concerned, the weirder, the better.
NANGLU: Why look at animals if they're not a little bit alien, right? Like, that was the first thing that got me when I was a kid. Watching National Geographic, like, with my dad, you see some strange invertebrate animal in the ocean, in its natural environment, and it's just like - it's more surreal than any movie.
KWONG: And one group of creatures that really gets his heart fluttering are worms.
NANGLU: Invertebrates, and worms in particular, are definitely gross. Like, I'm not going to deny that for a second. They can smell like chemicals, or sometimes they're covered in mucus, but they're also colorful. Some of them look ghostly. Some of them are under the sort of sea floor. But there's also, like, a real understated, sort of underappreciated beauty to them.
KWONG: And lately, he's been studying a group of worms called the Selkirkia - predatory worms, an inch long and covered in teeth.
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KWONG: Up close, they look kind of like the sand worms in "Dune." The Selkirkia live inside this tube that they build around them like a house. The worm waits inside until their next victim crawls by.
NANGLU: They have this structure called the introvert, which kind of, like, sits inside of, like, the analog of their throat. And when they feed, they kind of push it outwards, and it's just covered in hooks and spines and, like, teeth. And so, you know, from our perspective, these worms are pretty small. But if you're an invertebrate crawling along the sea floor, this thing is like a nightmare of just, like, predatory features all being pushed out of its throat at you.
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KWONG: And researchers have known that these Selkirkia worms existed in the Cambrian period. They have examples from the Canadian Rockies, from China, from sites in the Western U.S. But...
NANGLU: We have no examples of either them or their dwellings after the Cambrian period ends.
KWONG: So for decades, researchers thought that these worms died out at the end of the Cambrian period. And they're not alone - a ton of marine life was lost during that mass extinction.
NANGLU: This has sort of led to a lot of people thinking of the animals that came out of the Cambrian explosion being almost experimental in their nature. Maybe they - you know, they were, like, life's big - first, like, Big Bang in some ways. And then, afterwards, they didn't really persist all that long.
KWONG: But these worms may have in fact persisted.
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KWONG: Today on the show, the time-traveling worm with teeth - how Selkirkia worms showed up in the fossil record 25 million years after researchers thought they died out - plus, what that tells us about the boundaries of time itself. I'm Emily Kwong, and you're listening to SHORT WAVE, the science podcast from NPR.
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KWONG: All right, so this story began like a lot of research does - through some innocent digging. It was fall 2021. Karma and a group of his colleagues were searching through fossils housed at Harvard's Museum of Comparative Zoology. The fossils they were looking at came from this incredible site in Morocco called the Fezouata formation.
NANGLU: The fossils in Morocco are often articulated, so they look, you know, basically, some of them like they died yesterday. So they're preserved in exquisite detail.
KWONG: The sediment from this site was really good at preserving the soft-bodied animals that died inside, which are often lost to the fossil record. Now, the Fezouata fossils came from the early Ordovician period. The Ordovician period happened right after the Cambrian period ended and there was that big mass extinction. And one day, Karma and his colleagues noticed, in the fossils, this long, tubular body.
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KWONG: At first, they thought it was this cone-shaped animal from a group called the Conulariids.
NANGLU: But the shape was very different. That was the first clue that something was different.
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NANGLU: The style of preservation was different. And so I took one under the microscope, and I told Javier (ph), the PI of the lab, like, if this was the Cambrian we were looking through, I would say this is Selkirkia. But it shouldn't be here. These guys were supposed to have been gone from 500 million years ago.
KWONG: Right.
NANGLU: The site that we're looking at - 475 - so that's a 25-million-year gap.
KWONG: Wow. I mean, it's almost like meeting a time traveler. You know, you were, like, hanging out in this Ordovician party, like, looking at all the guests, and then this person shows up from, like, millions of years ago, and you're like, what do you - what are you doing here?
NANGLU: (Laughter).
KWONG: How did you get here?
NANGLU: No, totally. I mean, it's - it - you know, it's the kind of thing that, like, you have to blink. And you're like, OK, maybe I'm just deluding myself into thinking that this is something that it's not because that would be an exciting story.
And so the papers come out sometime later because, basically, in addition to the fact that we're running multiple projects simultaneously, we're also, like, spending a little bit of time convincing ourselves - like, is this truly what it could be? Let's exhaust every other possibility. Let's get comparative photos from our colleagues. Let's look at other locations. And, you know, after some time of thinking about it, basically, we came to the conclusion it could be nothing but this group, Selkirkia. And the implications of that mean the longevity of this group is, you know, massively expanded.
KWONG: So you and your colleagues published a paper in late March 2024, in the journal Biology Letters, sharing the discovery of this new species of Selkirkia worm. Karma, what was, like, the implication of this...
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KWONG: ...That these kinds of worms were showing up so much later than people thought?
NANGLU: So you can think of it almost in, like, terms of tiers of how broad the ideas go. So the first implication is this group was actually, you know, far from being a sort of oddity of the Cambrian period.
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NANGLU: And then if you take their oldest record back and sum it all together, 40 million years of time is a pretty impressive stretch to not have to change basically any component of your lifestyle. They're still building tubes.
KWONG: (Laughter).
NANGLU: They're still just sitting there with hooks on their faces, ready to eat unsuspecting animals that come by.
KWONG: When you looked at it and when you studied it, what about it allowed it to live for so long - for 40 million years?
NANGLU: Well, you know, that's an interesting question because I think it also strikes at sometimes the public perception of evolution - that it's this kind of evolutionary fray where, at every moment, things have to be adapting - you know, eyes and wings and appendages and things. But this is a pretty, you know, simple life, you might say. It's a worm. It's only a couple of centimeters long. It's whole body's a tube - builds a house around itself and doesn't see the need to do much more. The fact that it's so long - like, had such longevity, I think points to the fact that sometimes a very simple strategy, well executed, is very effective.
KWONG: Hmm. And what do you think was the thing that was ultimately their undoing? 'Cause, eventually, they did disappear from the fossil record.
NANGLU: Yeah. So - well, two things. One is it could be sort of the increasing prominence of predation. So if you imagine those early ecosystems I'd mentioned before, from the time before the Cambrian, we don't really have solid evidence for animals that had the capacity to eat each other for predation.
In the Cambrian, we obviously have animals that do that. We even have animals with their stomachs preserved, and you can see other animals inside of them. And then as time goes on, that becomes more and more prevalent. And in the Ordovician, we have much more active predators. We have animals that seem to have a better capacity, possibly, for, you know, sensing their surrounding environment.
KWONG: Yeah.
NANGLU: That being said, we have tons of worms in modern environments that employ basically the exact same strategy. So there's a combination of what's going on in the environment around you and then some component of what, to an outside observer, might look like luck or random chance.
KWONG: Yeah.
NANGLU: The other component is maybe they didn't go extinct.
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NANGLU: If we'd taken the narrative that existed a - you know, a few months ago, this is a group of animals that popped up in the sort of middle Cambrian. They lasted for about 16 million years, and then they went extinct. This paper pushes that by another 25 million years. That's not to say that another paper won't push it further in the future.
KWONG: It sounds like you also had to contend with this, like, boundary between the Cambrian and the Ordovician periods differently, right? Like, what was, like, a hard line in the sand of, like, death was not true for these worms. So how does this finding make you reconsider, like, the boundaries between different eras in time?
NANGLU: Well, it really plays into a much larger debate that's going on in research at the time - or at this time, rather. So we have events like a really classic narrative. During the Ediacaran Period - that's when life sort of got big. It got macroscopic. And the Cambrian explosion fills out most of the diversity that we see in modern environments as well.
And then during the Ordovician, we get much more complicated modes of life. We start to get an increase in speciation rates. Things start moving up into the water column more. So that's the traditional narrative. But some researchers have sort of questioned how much some of these events actually represent completely separate phenomena. And so sites like Fezouata are actually showing that some of these groups - not just this worm, but others, have actually made it across that boundary as well.
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NANGLU: Much has been said about the group called the radiodonts, which are a group of early arthropods, which were probably including many of the first top predators in these ecosystems - that many of them make it across the boundary, or at least some of them.
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NANGLU: So, you know, this kind of begs the question - how many other groups will have done this - made it across that boundary, and how many do we need to find before we start saying, OK, some of these boundaries, at least from the biological perspective - nothing to say about the geology - but from the biological perspective - maybe some of these boundaries are a little bit more fuzzy than we previously thought.
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KWONG: I mean, so what would you say is the value of doing research like this? Because, you know, there are so many ecologists today, like, rapidly trying to catalog the biodiversity we have now - like, ecosystems now. What's the value of trying to catalog the biodiversity back then?
NANGLU: Yeah, so, I mean, there is a sort of field and a way of thinking called conservation paleobiology, which, you know, basically posits that, to understand or predict the future, you need to understand the past. And so these tend to be on more recent time scales in terms of paleo, looking at how different, like, greenhouse environments or cooling events may have affected diversity patterns, which can help us, like, you know, learn things about climate change, which is pertinent to modern-day ecologists.
For me - and, you know, I'll just give the honest answer here 'cause I don't know how to give another one - but when looking at, you know, fossils like this, time periods like this, what's more important is that we're getting at the origination points of the entire marine biosphere. We're getting at the origination points of entire groups of animals that continue to exist today. So for me, it's more of a fundamental science question, like the fundamental sort of purpose of curiosity.
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NANGLU: There's intrinsic value there, too, to keeping people kind of inspired by the natural world.
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KWONG: Karma Nanglu is a postdoctoral fellow at Harvard Museum of Comparative Zoology. Karma, thank you so much for coming on the show and sharing this work with us.
NANGLU: Yeah, no problem. Anytime. I'm really happy you guys were interested in hearing about worms. You know, you can't always lock someone down for an hour to talk about worms and these ancient fossils and these sea communities. But, yeah, it's always fun to talk to you at NPR.
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KWONG: This episode was produced and fact-checked by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez. The audio engineer was Ko Takasugi-Czernowin. Beth Donovan is our senior director, and Collin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to SHORT WAVE from NPR.
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