Danielle de Carle

We found the first leech fossil that has ever been recorded.

Oh, yeah.

So parasitism is a type of symbiosis.

And symbiosis is basically just a situation where you have individuals from two or more species that live together in very close association for a long period of time.

And they're adapted for this purpose.

And parasitism is like a specific form of symbiosis where you have one organism that lives inside or on another organism.

That's called the host.

And the parasite gains nutrients at the expense of the host.

And it has some kind of adaptation for doing so.

So it's either eating little bits of the host or it's kind of stealing nutrients from the host.

So like you said, when we think about leeches, most of the time we think about ones that feed on our blood, right?

Or the blood of other vertebrates.

But today, there are lots of leeches that don't do that.

So some of them, they'll swallow basically anything that can fit in their mouths, or they'll bite off chunks of dead bodies and things like this.

And then we have...

Other leeches in the kind of modern biota, I suppose.

So they'll suck on the bodily fluids from things like crabs and shrimp.

They'll kind of attach and stick their mouth parts in the little membranous parts between the hard plates.

Oh my gosh.

And they'll suck out the bodily fluids in that way.

So the fossil that we found, it wasn't found alongside any real large vertebrates.

So we think that instead of parasitizing vertebrates, which is sort of the prevailing hypothesis for what the oldest leeches did, we think that our fossil instead would have either preyed on other animals by kind of swallowing them whole, or it might have been a parasite of invertebrates, of larger animals like trilobites.

They also included photos of some fossils that were beautifully preserved, but they weren't entirely sure yet exactly what they might be.

OK.

Another mystery.

Karma saw one of them.

Yes.

Another mystery.

So Karma saw one and he thought it might be a leech.

So he brought it to myself and our other co-author, Rafael Luama, who's also a leech scientist.

And he was very excited about how this might be a leech.

And instantly, Rafa and I both were like, no, I don't think so.

After we rejected Karma and we threw his first hunch out the window, we decided to get in touch with Andrew and Lauren.

And they were kind enough to share some photos of a lot of animals that they, or a lot of fossils from the Waukesha site that they hadn't yet identified, which included some other segmented worms.

And one that immediately leapt out at us was this one that we ended up describing as Macromizon, as the first fossil leech.

And this one did, in karma's defense, have lots of similarities to that first fossil.

But it wasn't the one he showed you, is what you're telling me.

Yeah, it had a little bit of extra detail in there that sort of made us feel really confident.

And the first thing in particular that we noticed was that big sucker that it has at the posterior end, which is something that's a huge hallmark of leeches today as well.

But you know, it's courage, right?

You had the courage to be wrong.

And because of that, we stumbled upon this amazing discovery.

If you hadn't had the courage to be wrong, we'd all still be leechless.

We'd be leechless.

That's true.

Yeah, it tells us a couple things.

First of all, it tells us that this group of animals, that leeches, are like 200 million years older than we thought they were initially.

It also tells us that

Despite the kind of prevailing sort of hypotheses at the time, it was unlikely that the first leech fed on vertebrate blood.

Instead, we think it was either a parasite of invertebrates or it was a predator.

And it also kind of tells us a little bit about the habitat of leeches.

So as Karma kind of mentioned earlier, most leeches today are either aquatic, living in freshwater, or there are terrestrial ones.

But we also have some kind of marine leeches.

And the prevailing wisdom before this new discovery was that those marine leeches represented sort of a single origin or a recolonization of the oceans, right?

Like the ancestor of this one lineage moved back into the oceans and

gave rise to a whole bunch of all the marine leeches that we see today.

Yeah, I think there's huge potential for discovering new fossils in collections that already exist.

I'm sure there are lots of projects just like the Riddler, you know, that generations of scientists never, they never found that one paper from the 70s that really kind of blew everything open, right?

And they just kind of put those things in a drawer and they're waiting to be rediscovered by new generations of people.

I think as well with new technologies, you know, again, with this, the Riddler, one of the technologies that they use to sort of get a lot more information was CT scanning, things like this, right?

So if we sort of subject the fossils that we do know about to further scrutiny, maybe we'll find even more organisms, like inside ones that we already knew, whether their bodies are physically there or whether there are traces of that activity.

I think there's huge potential.

Thank you so much for having us.