The Trouble With Trilobites


They’re probably the most recognizable fossils in the world. Flat segmented bodies bristling with antennae and legs. They’re what we think of when we think of life in the ancient sea. But trilobites are famous not just because they were so beautifully functional or because they happened to preserve so well. They’re known the world over because they were everywhere. For more than 270 million years trilobites thrived all over the planet, scouring the ocean floor from Siberia to Morocco and Canada to Australia. In their time they were the planet’s most successful and possibly its most abundant animal until …they weren’t. The trouble with trilobites is pretty much the same trouble we have with understanding why any animal that was once so abundant can totally disappear because trilobites were survivors. The history of these creatures shows that they practically invented survival in order for them to finally go extinct and leave no direct descendants. Nature had to try to kill them like four different times. Let’s start about 540 million years ago, just before the dawn of the Cambrian period. Back then all life on Earth was in the sea and most of it was squishy like sponges, worms, and jellies. Yes, there were some mollusks and simple shelled creatures like brachiopods. But by and large if you were an animal you didn’t have to worry about protecting yourself from predators. Then about five hundred and twenty-one million years ago the first known trilobites appeared in what is now Siberia. They may have evolved from small thick-skinned segmented worms like spriggina, which I gotta say do seem to share a family resemblance. But, trilobites took the benefits of physical complexity much further. How much further? Well, they had legs for one thing, and they developed complex eyes and a sophisticated digestive system. Plus, they were covered from their rounded heads to their many segmented feet in an exoskeleton made of calcite and chitin. The trilobite was a true arthropod; a founding member of the group that includes today’s arachnids and crustaceans and every insect. And equipped with all of these awesome new features it dominated the Cambrian seas; feasting on a diet of worms and other unprotected invertebrates, it flourished and diversified quickly. Within 40 million years of its first appearance in the fossil record, there were at least 60 different taxonomic families of trilobites ranging from the googly-eyed asaphus To the familiar elrathia, probably the most common trilobite found in the U.S. today. For millions of generations they thrived by laying low on the ocean floor, but the seas the Cambrian were becoming increasingly hostile. The Cambrian, after all, was when predation first appeared on Earth, with animals hunting other animals, and trilobites left behind lots of fossils with bite marks on them to show it. But by the time the Cambrian came to a close, trilobites, like many other animals had picked up some new tricks. The cutest of them … enrolling. Judging by the segmentation of their bodies, some kinds of trilos like the genus flexicalymene, developed the ability to curl themselves up into little balls like Modern pill bugs or armadillos do, in addition to probably being adorable, it made it harder for new-fangled predators to sink their teeth into them. But, not all the threats to our little armoured friends came from other animals. Starting around 445 million Years ago, Earth’s climate dealt a double blow to life in the seas. First, a dramatic cooling changed the ocean currents and choked off the supply of warm water foods like algae. Then a period of glaciation Locked up lots of Earth’s water, which dramatically lowered sea levels. This twofold impact known as the Ordovician-Silurian Extinction, wiped out about 25% of all taxonomic families, including about half of trilobite families. The families of trilobites that remained were mostly ones that were well adapted to this new world like Dalmanites, which fared well in cooler seas. Then, of course, trilobites had another problem to deal with. As the environment continued to change, other organisms had to survive too, under constant evolutionary pressure to adapt or die. The new adaptations that had come about during the Cambrian, like pincers, spikes, and claws, were really starting to come in handy. But there was one adaptation that may have been trilobites kryptonite …jaws. About 420 million years ago, the first jawed fish appeared and some experts think that these new predators put even a more evolutionary pressure on the trilobites. Sure enough, about 20 million years after the first appearance of jaws, new variations of spiny, spiky trilobites started showing up in the fossil record, like Dicranurus here prickling with curved spines. But Earth’s environment had still more surprises in store, starting around 375 million years ago when…well we don’t know what happened exactly. But we do know what the results were, suddenly big swaths of carbon rich sediments were laid down and oxygen levels in the water started to drop. Reef communities began to collapse, and those new fish with jaws managed to get by as did new life forms on land like plants and insects. But, most jawless bottom feeders, including the trilobites, vanished. In the end, this series of unfortunate events known as the Late Devonian Extinction wiped out about 20% of the animal families in the sea, including all but four families of trilobites. The trilos were on the ropes and the final blow came with the greatest die-off in Earth’s history. 252 million years ago something changed radically in our planet’s atmosphere. Some scientists think it was an asteroid impact. Others point out that it was also a time of tremendous volcanic activity. And on top of that, Earth’s landmasses were changing, which altered climate patterns yet again. Whatever came knocking for the trilobites, it came quickly. Within probably less than a million years, 70% of the species on land were gone and 95% of those in the sea, including the last surviving species of trilobites. It took the worst catastrophe in the history of life on Earth to wipe out the trilobites; an event known as The Great Dying. Now it may not sound like it, but the tale of the trilobites is really the first success story for the entire animal kingdom. Sure they’re gone now, but at the time they were the most advanced animal the world had ever seen, and they went on to become one of the most diverse groups of extinct organisms on record; with over 15,000 described species. And they survived for way longer than many other types of animals. They were around longer than the non-avian dinosaurs and longer than mammals have been …including us. So the question to ask about trilobites might not be why they went extinct, but how managed to endure for so long. After all, today we are one of the planet’s most successful animals, so the trilobites troubles may someday be our own.

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Reader Comments

  1. Gitana Maldita

    Trilobites, ammonites & crinoids are my besties because they were so beautifully formed. Also stromatolites, but they were kind of alien!
    I'd love to see some of Pilbara Craton dear PBS Team 😍

  2. Jeffrey Evans

    i imagine that trilobites were too successful and managed to build vehicles for transportation that burned fossil fuels and produced CO2 that polluted the atmosphere to the point that the seas turned into acid .

  3. GregoryTheGr8ster

    I'm just glad that the trilobites did not destroy the planet like we are. We will cause our own extinction. I just hope that my consciousness can be captured and preserved in a simulation or artificial neural network.

  4. Mlogan11

    At least they were likely just victims of events outside of their control and didn't "self-extinct" due to destroying their own habitat- like (cough) mankind.

  5. Lucky Tailor

    I disagree with their Extinction I found a living specimen in freshwater approximately 20 years ago in Georgia in the United States what I thought was a small fossils I'd like to dry it off and it moves it was not dead it was not a fossil it was alive and it 50 and national Audubon society book fossils description 280 there is hope

  6. Jack Hartford

    New channel! And I just watched this video, and then moved on to other things, and then realized, I hadn’t liked, or subscribed!

  7. Adventure Fighter

    The most surviving species are maybe coelacanths! According to the wiki, they survived many periods! Maybe like 6 periods?

  8. Ryan Nu

    Literally the earths first dominant species even if they failed it’s still amazing the ups and downs of earths biodiversity, earths even seen multiple sentient life forms but only 3 including us to get this far.

  9. reuireuiop0

    OK I surrender.
    It is trilobite, not Tribolite.

    I found -lite more suiting, as, well, most of 'm are found as fossils; stones, in other words, validating a -lite ending as often used in geology.

    Whereas …bite …
    That's not something they're known for, biting.

    T-R-I-I-I-LO- bite!
    Trrrriiilooo-bite

    Still doesn't sound like it.

    TRIBOLITE !!!

  10. Nova Stocker

    Maybe if we’re lucky they can still be alive, just somewhere we haven’t been able to find them. Like the bottom of the ocean today, I mean it’s still so unexplored. But I guess it’s very very unlikely.

  11. Natsume Neko

    my new favorite channel! (it is like a nat geo/ discovery channel but tho short, way more fun and not boring to watch. just my personal opinion tho.) glad I found this channel, tbh, i have been searching nice and educational videos (like kid encyclopedia-like shows) but i couldn't bc all i see are these top 10 rare/extinct/big, etc vids everywhere in youtube that i don't even know if the info could be trusted or what XD..but really glad i found the one! thanks for this!

  12. Fluffyhead

    I swear I’ve seen a creature that is alive today that looks just like the trilobite, that is supposed to be evolved from prehistoric times, I can’t remember what it’s called, some kind of medicine is extracted from it, it may be a different species correct me if I’m wrong

  13. Swike

    Trilobites are so the Chuck Norris of the Animal kingdom that i won´t be surprised if some lost family of Trilos be found on the Oceans depths

    #TRILOSRULES

  14. WWTormentor

    Perhaps the key to their survival was the fact that during majority of their existence there was little to no predators that could kill them. It seems easier to adapt to your environmental changes when you don’t have to fight off predators and your offsprings have higher chance of survival and reproducing which can increase the odds of mutations to better adapt to your environment.

  15. Barry Werdell

    Wonderful, fellow PBS Eons viewers if you want to know more about Trilobites try
    David Attenbourogh's "First Life, Conquest" here's the link
    https://www.dailymotion.com/video/xylykp

  16. Donald Piniach

    Remember 99.9999% of all species that ever existed are extinct. Extinction is the norm. The expected end point.
    Even the T Rex only survived 6-7 million years.

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