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Animals eating other animals seems like a tale as old as time, but it's only almost that old. Predation had to evolve in the Ediacaran period -- so let's look at early almost-predators like Auroralumina, Kimberella, Ikaria, and whatever punched holes in Cloudina.

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Sources:

Ikaria:
https://pubmed.ncbi.nlm.nih.gov/32412628/
https://www.pnas.org/doi/pdf/10.1073/pnas.2001045117
Kimberella:
https://www.cell.com/current-biology/fulltext/S0960-9822(22)01699-2
https://www.nhm.ac.uk/discover/news/2022/november/evidence-worlds-oldest-meal-may-have-been-discovered.html
Cloudina:
https://www.jstor.org/stable/3515782

General:
https://arxiv.org/pdf/2212.00899.pdf
https://doi.org/10.1016/j.tree.2008.07.015
https://doi.org/10.1017/S1089332600001133

Images:
https://www.eurekalert.org/multimedia/984654
https://commons.wikimedia.org/wiki/File:Kimberella.jpg
https://www.gettyimages.com
https://www.eurekalert.org/multimedia/711455
https://www.eurekalert.org/multimedia/989702
https://commons.wikimedia.org/wiki/File:1._%D0%94%D0%B8%D0%BA%D0%B8%D0%BD%D1%81%D0%BE%D0%BD%D0%B8%D1%8F_-_%D0%B8%D1%81%D0%BA%D0%BE%D0%BF%D0%B0%D0%B5%D0%BC%D0%BE%D0%B5_%D0%B6%D0%B8%D0%B2%D0%BE%D1%82%D0%BD%D0%BE%D0%B5_%D1%8D%D0%B4%D0%B8%D0%B0%D0%BA%D0%B0%D1%80%D1%81%D0%BA%D0%BE%D0%B9_%D0%B1%D0%B8%D0%BE%D1%82%D1%8B_(%D0%A1%D1%80%D0%B5%D0%B4%D0%BD%D0%B8%D0%B9_%D0%A3%D1%80%D0%B0%D0%BB).jpg
https://commons.wikimedia.org/wiki/File:Yorgia.jpg
https://commons.wikimedia.org/wiki/File:Charnia_masoni_Charnwood.JPG
https://commons.wikimedia.org/wiki/File:Yarnemia_acidiformis.jpg
https://www.inaturalist.org/observations/1917776
https://www.nature.com/articles/s41559-022-01807-x
https://www.eurekalert.org/multimedia/690364
https://commons.wikimedia.org/wiki/File:Elrathia_kingii_fossil_trilobite_with_healed_bite_mark_%28Wheeler_Formation,_Middle_Cambrian;_House_Range,_western_Utah,_USA%29_3.jpg
https://commons.wikimedia.org/wiki/File:Vendian_Fauna_(5528130308).jpg
https://commons.wikimedia.org/wiki/File:Kimberella_quadrata.jpg
https://commons.wikimedia.org/wiki/File:Kimberella_diorama.jpg
https://www.eurekalert.org/multimedia/966090
https://commons.wikimedia.org/wiki/File:Kimberella_NT.jpg
https://www.eurekalert.org/multimedia/928075
https://www.app.pan.pl/archive/published/app63/app004672018.html
https://commons.wikimedia.org/wiki/File:Ikaria_wariootia.jpg
https://commons.wikimedia.org/wiki/File:Spriggina_floundersi_-_MUSE.jpg
https://www.eurekalert.org/multimedia/687332
https://eurekalert.org/multimedia/928076
https://commons.wikimedia.org/wiki/File:Ikaria_wariootia_(cropped).jpg
https://www.mdpi.com/2075-1729/12/2/136
https://www.nature.com/articles/s41598-019-56317-x#Fig1
https://www.eurekalert.org/multimedia/725563
https://www.nature.com/articles/s41598-017-05753-8#Fig8
https://www.nature.com/articles/s41598-017-05753-8#Fig4
https://commons.wikimedia.org/wiki/File:Cloudina_NT.jpg
https://commons.wikimedia.org/wiki/File:Natica_hebraea.jpg
https://commons.wikimedia.org/wiki/File:Cloudina_fossils_(Neoproterozoic;_Corumba,_Brazil)_(45453979394).jpg
https://www.nature.com/articles/s41598-021-90768-5/figures/1
https://commons.wikimedia.org/wiki/File:Ediacaran_trace_fossil.jpg
https://www.eurekalert.org/multimedia/881103
https://www.eurekalert.org/multimedia/919689
Roughly 600 million years ago, the world would have been a very peaceful place.

This is the Ediacaran period. The land is barren and the ocean is dominated by a thick, rich, gooey mat of bacteria and other microbes growing on the ocean floor, occasionally broken up by some of the earliest known animals.

These are simple, mostly soft-bodied and often immobile things, never daring to venture beyond the nutrient-rich mat. For the most part, the creatures here seem to have left each other alone, getting all the nutrients they needed from the water or microbial mat below them. In fact, there may have been no big, active predators at all, a scenario scientists have described as a kind of evolutionary shangri-la , after a fictional, peaceful paradise.

But then… everything changed, when some of the animals began to eat each other. [♪ INTRO] Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30-day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. Earth’s fossil record is full of predators, like Tyrannosaurus rex or Megalodon.

Even as far back as the Cambrian, we have predators like Anomalocaris. But the earliest truly complex animal ecosystems appeared in the Ediacaran, and during this time, big, obvious predators are distinctly missing from the fossil record. Part of this is certainly due to how simple animals were at the time.

Some fossils, like Dickinsonia and Yorgia and the fractal-shaped rangeomorphs, don’t even appear to have a mouth, possibly absorbing everything they needed directly through their skin. But this raises the question of how we got from baggy, passive blobs to big, active predators. We know predation, which we can define as getting nutrients and energy by killing other living things, is technically a very old life strategy, much older than animals.

The earliest definitive fossil evidence is from about 780 to 740 million years ago, but single-celled organisms may have been preying on each other for billions of years. And animals were likely consuming microbes from the very beginning. Some may have snagged larger prey as well.

Auroralumina, a fossil dated back to 560 million years ago, has been interpreted as ancient, immobile relative of jellyfish, for example. Now because modern jellyfish are typically predators, the scientists who found it suggest it was too, snagging passing algae or plankton from the water. But this is still a far cry from the more active predators that would come later.

So how did animals first start actively pursuing and capturing prey? Well, It turns out it’s not as simple as just turning around and taking a bite out of a neighbor. The emergence and diversification of animal predators may have been a risky bet, one that would have needed specific conditions and multiple adaptations.

But, as we’ll see, by looking at the fossil record, we can see some of the earliest iterations of these adaptations in action, like the ability to sense and chase down prey, and to fight and kill it. Even digesting it may have been a big leap. So, here are some examples: One fossil of interest is a little creature called Kimberella.

Dated back to about 558 million years ago, Kimberella isn’t quite what you’d think of as a predator. It likely nommed on the bacterial mat along the sea floor, making it more of a grazer. But it had something that would be really important for future predators, the ability to move in search of food.

We think this because Kimberella fossils have often been found alongside trace fossils of trails in the sediment. It also had a second important characteristic that complex predators would need: a gut. In 2022, scientists analyzed chemicals found in the rock making up Kimberella’s remains.

The chemical traces they found most likely resulted from Kimberella eating and digesting microbes or algae. This means that Kimberella had adapted its insides to actively break down and absorb nutrients from other living things. It was a predator, just not one at the level of a cheetah subduing its prey… yet.

Another important fossil is called Ikaria. This was an animal from around 550 million years ago that seems to have actually lived and burrowed underneath the microbial mat along the ocean floor. Their fossils have been found in rocks in the Flinders Ranges of South Australia, about 400 kilometers north of the city of Adelaide, and usually consist of trace fossils of tiny, meandering tracks about 1 to 3 millimeters wide.

Technically because these are trace fossils and you can’t always be 100% sure this animal made this specific trace, you’re supposed to use the name of the trace which is… this. But researchers have also found the critters themselves so we’re gonna stick with the say-able name. While many of the fossilized trails we have found of Ediacaran animals seem to be those of meandering grazers, like Kimberella, Ikaria seems to have moved with more of a purpose.

We can see their fossil tracks cross into body fossils of other animals, like Spriggina, and even turn towards them, suggesting it was eating them for nutrients. Now technically, we don’t know if the other animals were alive or dead when Ikaria found them, which means Ikaria may have been a scavenger rather than a predator. The scientists who first wrote up this finding think that’s the more likely case.

Nevertheless, it displays something somewhat unique in the fossil record for the time, and something later predators would definitely need: the evolution of a sensory system capable of detecting and tracking down food. And other fossils from this time may also show sensory hunting. Another kind of burrowing trace fossil, known as Treptichnus, seems to show that the critters who made the burrows were poking around as if they were searching for something, like prey.

The burrows closely resemble those of certain predatory worms alive today. Ikaria may not have killed its prey, preferring to scavenge, but this next fossil may have. Meaning, finally, we may have clear fossil evidence of an active predator.

It’s named… well, actually this predator is unnamed because it hasn’t been found! But it’s known from the evidence it left behind: holes bored into the shells of a creature called Cloudina to get at the tasty whatever-it-was inside. Known from fossils in central China, Cloudina were small, likely worm-like creatures that lived in the sediment.

About 1 to 10 millimeters in length, Cloudina lived in little tube-shaped shells. So how do we know there was a predator? In 2003, scientists examined a collection of Cloudina shells and found that about a fifth of the shells had these weird, straight holes drilled into them.

Always drilled in roughly the same area, not too far down, but below where you might expect the head to be. And this doesn’t seem to have been the result of some breakage or accident. When the scientists examined fossils of a similar species, Sinotubulites, which lived alongside Cloudina, no such holes appeared.

If it was an accident, we’d expect it to be more random in placement, not just in this one repeated spot, and to affect Sinotubulites as well. What’s more, whatever made the hole seems to have killed the Cloudina. None of the shells seem to show any evidence of healing.

Now this doesn’t seem that special, but think about it. This predator would have had the ability to find its prey, and also distinguish it from other species like Sinotubulites. It could also target weak points, since the holes in Cloudina aren’t randomly placed.

Targeting this one spot may have made it easier to avoid any retaliation from Cloudina. Or maybe this is where the tastiest parts were. So this wasn’t just a predator, but a specialized one!

Today certain molluscs hunt in a similar way, using their spiky tongue-like radula to drill inside their prey. This also possibly shows why evolving more active predation was a big deal: it was risky. Cloudina may have been able to fight back.

In fact, becoming a predator at all may have been risky. Becoming a specialist like the Cloudina-eater, or becoming a predator at all, means giving up other adaptations you might have used to get energy. Nevertheless, we can see evidence that as time went on in the Ediacaran, animal-on-animal predation was on the rise.

This may have kicked off an ecological arms race, as we can see evidence of prey species adapting in response. The emergence of vast Cloudina reefs growing closely together may be a result of a strength-in-numbers-type defense against predators. Scientists have also found herbivore trails that start curvy and meandering, only to abruptly turn and break away in a long, straight line.

You can definitely picture that animal being ambushed and running for its life, which is how some scientists read it. Avoiding predators may have also spurred grazers towards burrowing, or to break loose from the bottom as free swimmers. Over time, the rise of active predators and the arms race they kicked off changed much about the ecosystem.

The once-vast mats started to disappear as grazers became more common. This decline was likely accelerated by burrowing animals looking for prey, or looking to avoid predators. Meanwhile, the animals themselves were changing.

Anti-predator defenses, such as hardened inner and outer skeletons and armor, evolved. By the next geological period, the Cambrian, predation becomes a major part of life, and we finally get big, unambiguously predatory species appearing in the fossil record – like the terrifying Anomalocaris. Some scientists have even pointed to the arms race between predator and prey as being the driving factor behind the Cambrian explosion.

Whether that’s true has been debated, but it’s undoubtedly a big part. We don’t think of predation as being something that’s difficult to arrive at. After all, if you can eat something, why wouldn’t you eat it?

But it turns out there’s still a lot to learn and uncover about the evolution of predation — and of early animals in general, of course. The Ediacaran is one of the most consequential, but also the most poorly understood, turning points in Earth’s history. But by examining the fossil evidence we do have, we can see the development of the suite of specialized adaptations necessary for animal predation to occur.

And maybe, just maybe, picture that very first animal that decided to go for a munch. The journey that these little guys took to become the first predators all feels… a little unlikely. And if you think about it, it’s also pretty improbable that we even have these fossils to begin with!

So if this story has made you think about other unlikely events that have shaped our world, our friends over at Brilliant have just the course for you. It’s called Perplexing Probability, and it explores some of the most counter-intuitive and surprising paradoxes out there. You’ll learn the tricks of the trade to master the most fundamental puzzles in probability, and hopefully develop an appreciation for any time in our world’s evolutionary past that some little creature beat the odds.

And that’s just one of the many courses you can explore with Brilliant, the online learning platform with thousands of interactive lessons in science, computer science, and math. You can try it for free for 30 days at Brilliant.org/SciShow or by clicking the link in the description down below. That link also gives you 20% off an annual premium Brilliant subscription.

Thanks to Brilliant for supporting this SciShow video! [♪ OUTRO]