Thanks to Curiosity Stream for supporting PBS Digital Studios Crocodiles. Horseshoe crabs. And of course … tuatara! They’re all animals that have persisted
for millions of years, said to have gone unchanged since the days of the dinosaurs. So, like, living fossils. Right? Well, no, not really. When you look at the history of life on Earth,
you see lots of major changes. In one part of the tree of life, you’ll
find a lineage of lobe-finned fish that gave rise to amphibians. In another, a branch of feathered dinosaurs
evolved into birds. And a subset of adorable little hoofed mammals
even developed into whales. But there’s a whole category of species
that apparently didn’t get the memo that dramatic change is where it’s at. These are things like your nautiluses, your
coelacanths, your ginkgo trees — organisms that look basically the same today as they
do in the fossil record. People call them “living fossils.” But, at the risk of being “that guy,”
the idea of a “living fossil” is kind of problematic. Really, the only guy who can get away with
using that term is Charles Darwin, because — well, he coined it more than 150 years
ago. In 1859, he pointed out that some animals
— like the duck-billed platypus and the lungfish — seemed to have held onto the same basic
body plan for millions of years. And Darwin figured, that was because there
was no evolutionary need for them to change. It was an important insight. But since Darwin’s day, this rather simple
idea has gotten bundled up with a bunch of misconceptions about evolution. Today, the term “living fossil” is sometimes
taken to mean that some organisms evolve, while others don’t. Or that living things only evolve … some
of the time. But just one of the problems with the idea
of “living fossils” is that there are actually many plants and animals that look
a lot like their distant ancestors. If the definition of a living fossil is an
organism that’s basically unchanged over long periods of time, then we got a whole
world of living fossils around us! For example, jaguars and gray wolves would
fit that description, because fossils that look just like them can be found as far back
as the last Ice Age. And … we’d be living fossils, too! (Some days, to be honest, I feel like one
myself.) But, the oldest remains of Homo sapiens are
more than 200,000 years old, and those fossils look just like us. So, as a descriptive term, “living fossil”
doesn’t seem very useful, at least on smaller geologic time scales. But another, bigger problem with this idea,
is that it makes organisms sound like they haven’t changed at all, when in fact, they’re
the results of millions of years of evolutionary pressure. Just take a look at one of the most famous
so-called living fossils — the crocodylians, like alligators, crocodiles, and gharials. Today’s crocodylians are all aquatic ambush
predators. They stay close to the water’s edge and
attack whatever prey that comes within range. And we know from the fossil record that, way
back in the Jurassic Period, there were croc-like ancestors — called crocodylomorphs — that
looked more or less like the crocs we know today. But look into the even deeper past, and you’ll
find a staggering array of croc-like reptiles unlike anything we see now! More than 200 million years ago, in the Late
Triassic Period, some of these reptiles lived not at the water’s edge but on land. I’m talking about truly terrifying carnivores
like Postosuchus, which basically looked like a four-legged T. rex. By contrast, in the Late Jurassic, there were
others, like Dakosaurus, that spent their lives entirely out at sea. These reptiles lost their body armor, had
feet that looked like flippers, and used shark-like tail fins to move through the water. So, crocodiles didn’t just slide into the
water and stay the same since the Triassic. Sure, you can find a fossil of a croc ancestor
that looks more or less like a modern one. But what you’re not seeing are all of the
forms of crocodylians that have since been lost — ones that show us how much their family
has changed. Which brings me to one last point. And that is: Life is evolving all the time,
even if we can’t see it! Just because an organism might look much like
it did millions of years ago, that doesn’t mean that it hasn’t felt the effects of
evolution. Genes, if not anatomy, can show us that life
is constantly evolving. For your consideration, there’s the tuatara! Show me your best tuatara I just got a neck cramp This reptile from New Zealand looks straight-up
like a lizard, but it actually belongs to an entirely separate group of reptiles called
Rynchocephalians. These reptiles thrived over 200 million years
ago, but the tuatara is the last remaining member of their family. Because of its ancient pedigree, the tuatara
is often called a “living fossil” Oh man I’m a living fossil! but its DNA proves that it has changed over
time — a lot. A study in 2008 compared the mitochondrial
DNA from both modern and fossil tuatara bones. And it found that this reptile is undergoing
faster genetic change than any other vertebrate. Its bones may resemble those of its Jurassic
relatives, but at the molecular level, the tuatara — like all of us! — is changing
all the time. So, sometimes evolutionary changes are big
and obvious, but sometimes they’re almost imperceptibly small. Even the most ancient-looking organism carries
a record of its history in its anatomy and its genome, and together they show us that
evolution is always at work. PBS Digital Studios is sponsored by Curiosity
Stream, where you can stream documentary films, and programs about science, nature, and history,
including exclusive originals! And if you’re watching me right now, you should probably check out Planet Dinosaur, a three-part BBC series about the latest discoveries from the days of the non-avian dinos. Curiosity Stream offers unlimited streaming,
and for you Eons viewers — because I like your face! — the first two months are free
if you sign up at and use the promo code…wait for it… EONS. Now what do you want to know about the story of
life on Earth? Let us know in the comments. And don’t forget to go to
and subscribe! But the fun doesn’t end here! Do yourself a favor and check out some of
our sister channels from PBS Digital Studios.

Author Since: Mar 11, 2019

  1. Here's a series questions. Is everything evolving at the same rate? Do we have evidence for this? Have some species changed genetically very little? Are they still genetically compatible with some of their ancient ancestors?

  2. I love when its your turn to present the video, but you seriously need to speak slower, especially for those that are not English native speakers.

  3. Master Therion,
    Dinosaurs were not dangerous. They were plant eaters or they would have eaten the entire human population. You can read this in The Bible: Job 40:15 thru 41:34. The behemoth was a land dinosaar and leviathan was a sea dinosaur. Notice the men who tried to tie them down were not killed. This may indicate that they had a temperment similar to elephants or oxen.

  4. I thought living fossils were things we only knew from the fossil record and assumed had gone extinct, which we subsequently discovered hadn't gone extinct because we found a living specimen/relative. :/

  5. But what does all that genetic change amount to then? Behavioral changes? Physiological changes that don't involve bones?

  6. That's thing though. What was living back those millions of years ago and died off were of a different species within the same genus. If the latter (most recent) species of that genus appeared in the modern day and looked exactly like its ancestor than to some extant we can't call it a living fossil unless it was the extinct species itself, this include their unique attributes.
    To lay it out, we have Pristichampsus, a nimble predator that is able to run like Cheetah in comparison to its recent and distant cousin the Cuban Crocodile. Both evolved similar body designs, but one is more modern than the other, Pristichampsus were still living today than it would be called a living fossil. Any of the animals that went extinct before or when after the first Cromagans and Neanderthals appeared, and are still living today can be considered living fossils.

  7. If you keep saying he talks really fast. It's not that you're just slow and not really interested. I have no problem keeping up with this gorgeous man!

  8. Legacy species might be a bit better as often these species have archaic features while this video pointed out being modern genetically altered/ evolved species

  9. 1:33 – you realize that "living fossils" applies to those who didn't change for hundreds of millions of years, right? Last Ice Age was not even 100,000 years ago.

  10. Trying to think of something Smart and insightful to say about how this video is really good and informative, yet here I am only being able to think about how cute the guy is…so sorry…

  11. I think they mean "living fossil" as in environmental factors haven't caused a species from millions of years ago to speciate

  12. I thought that "living fossil" was a term used for an animal that was discovered in the fossil record before a living specimen was discovered.

  13. That is just a saying of when animal that hasn't changed much physically despite the many animals who have changed radically since a certain time frame. Ofcourse animals change at the genetic level. Good to explain to people though, because many do not know this.

  14. Of course living fossils are a "thing" … just don't take the term too literally. Some organisms have not changed their morphology that much in millions of years. That's an interesting phenomenon. It means their body plan is successful and did not need much tweaking. Just because they may have changed in some other respects doesn't mean you have to write off the term "living fossil" altogether. Don't be ridiculous.

  15. Absolutely living fossils are a thing how come Coelacanth Green keeps getting work?

  16. What about vampire squids? If I remember correctly, the species was present since the Jurassic period. If it was the same species, genes would be very similar, right?

  17. While I kind of agree, I think you're very much missing the point. You can't compare a ceolacanth, who has gone through minimal evolutionary changes for over 400 million years to humans that just appeared a couple hundred thousand years ago. If we remain basically unchanged for the next 100 millions years from now, then maybe we could call ourselves living fossils.

  18. I always get confused when they say they compared dna from fossils with modern animals. Aren't fossilised bones just bone shaped rocks and minerals?

  19. But the last ice age ended like 12,000 years ago. Could you be a bit more specific about the jaguars etc. Did they look similar from before the ice age started or did they change into basically modern versions during the ice age?

  20. This is why we can't have nice things. living fossils are a perfectly valid idea, it should be a term of respect for a lifeform that has hit its 'sweet spot' as it were. a goal all life should aim for, to have one's basic body plan be successful in most/all likely scenarios for eons.

    but because humans are imbeciles and cant even grasp the basics of evolution beyond a shallow simplified view like "more change = more evolution = more better", it has become this foolish idea. Shame. shame upon us all.

  21. 2:34 postosuchus isn't a crocodylomorph it's rauisuchian but both rauisuchian and crocodylomorphs are in loricata clade

  22. You claimed you were going to debunk the living fossil idea. Then you explained why living fossils were a thing. Then you pretended you'd debunked something that you'd confirmed.

  23. I always understood that "fossils" were the preserved remains of ancient life; therefor there was no such things as "living" fossils.

  24. Could you consider that becoming resistant to a sickness/illness is an evolution ? Does the immune system getting stronger becomes a proof of evolution?

  25. I believe many people would love to see an “in depth lengthier video” on human evolution based on the evidence throughout the fossil record to this point. Early life of all sorts is great, but I want more insight on all of US on this planet.

  26. I believe that the sun is the answer to life, and our everlasting change and adaptation. The radiation we receive from being in sunlight might be at very low levels, but since we breed for hundreds of thousands of years, that particular level of radiation is what leads creatures towards 'controlled mutation' or known as evolution. The particular muscle groups and bones we have in our bodies that are used most, or even used less during this process show very strong changes over the course of x million years. If you believe in evolution of the homo sapiens from monkeys, then you might notice that since we walk upright, we went from a 4 handed + 4 armed creature to a 2 legged 2armed creature with feet. The neglect our other two hands took over time ended us up with just two hands. The reason this happened was because our ancient ancestors traveled, almost non stop. I guess because they were tribal, and multiplying at faster rates. I think that our technological breakthroughs lead to the human races' rapid expansion and multiplication. But I digress, I think that radiation is the missing variable.

    Radiation calls rapid aging in organisms, it has also been known to change genetics and DNA rapidly in high exposure. This is perhaps the reason why as our planet goes from one extreme to another in temperature, you see new forms of life and drastic changes in genetics (as well as genetic change reduction). Animals get larger, or smaller depending on that level of radiation. From dinosaurs to handheld lizards and little birds. Not necessarily temperature, but radiation exposure. Imagine, there were times of mass volcanic eruption, ice ages, meteorites and asteroids. These things, rapidly kill off species. But they do more than just that, they alter our layers of atmosphere leading to different levels of radiation exposure. It seems as if this planet has a solution to every destructive event, as if it is just meant to be that we exist. Even humans cannot break it. If the human race were to kill off all life on this planet through war and other destruction, life would still find a way.

  27. See Lana I was right!
    Archer: Gee, I don't know, Cyril. Maybe deep down I'm afraid of any apex predator that lived through the K-T extinction. Physically unchanged for a hundred million years, because it's the perfect killing machine. A half ton of cold-blooded fury, the bite force of 20,000 Newtons, and stomach acid so strong it can dissolve bones and hoofs.

  28. Honestly, I still like the term to describe creatures that resemble their ancient ancestors, it's just a shame that people just love to take things literally.

  29. leopards and wolves arent fossiles… they are the real bones… deinosuchus……????? aligators and crocodiles have barely changed especially when you think its been over 65 million years…. coelacanth has barely changed for 360 million years…

  30. Ive watched so many video im starting to get these jokes on an educated scale. Like oh i get that now.

  31. "One by one, the classic examples—horseshoe crabs, coelacanths, cycads, and more—have turned out to be very different from the fossils that they apparently resemble, either at a genetic level or through subtle physical changes. Their recognizable nature is a red herring—these creatures simply did not exist in their current form millions of years ago." – Ed Yong

  32. The Dragonfly, fossils have been found from 300 MYA that are almost exactly the same as today's insects. I agree the term "Living Fossil" may not be scientifically correct, but it is a term which can describe a particular species in few short words without a lot of explaining.

  33. You should take some lessons from Hank and Olivia on how to talk to your audience instead of talking to the camera.

  34. Tuatara being the last of Rynchocephalians… like us being the last of humans DX (I'm sorry I'm really bummed about that…how cool would it be meeting someone like "I'm half Neanderthal and quarter Denisovian ")

  35. A Living Fossil Is a creature scientists thought was extinct million years ago but were found surprisely alive today, like the coelacanth

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