Thanks to Curiosity Stream for supporting
PBS Digital Studios. This creature is an extinct relative of horses
and rhinos, known as a chalicothere. And, this creature? It’s also a chalicothere. Even though they look pretty different, both
of these animals lived at the same time, and in the same places, and they did the same
things. They’re both closely related to each other,
and to horses and rhinos. And they both developed highly specialized
adaptations that helped them exploit their main source of food: the leaves at the tops
of trees. The first animal is known as Chalicotherium
, and it wound up having enormous arms and walking around on its knuckles, kind of like
a gorilla. The other is called Tylocephalonyx, and it
turned out to look a little more horse-like, but with a longer neck, and this weird, bony
dome on its skull. So, what happened? How did two of the same kind of animal, living
in the same place, end up looking so different? The answer is parallel evolution. You can’t really talk about the history
of life without talking about natural selection — the process by which living things can
become more likely to survive, and to have offspring that will also survive, if they
become better adapted to their environments. And chalicotheres are an especially great
example of how this process actually works. Because, in evolutionary terms, “better”
can mean a lot of different things. Success can take many forms, even for organisms
that live in the same environment and face the same challenges. Before they diverged into different types,
chalicotheres first showed up in Asia around 55 million years ago, during the Eocene Epoch
of the Paleogene Period. They soon made it to North America, Europe,
and eventually to Africa. During the Eocene, rainforests were widespread,
and they became home to a new group of herbivores: hooved animals called perissodactyls, which
today include horses, rhinos, and tapirs. “Perissodactyl” means “odd-toed,”
and like other members of this group, early chalicotheres had hooves — although their
hooves were split in two, which was kind of strange. But as the Eocene ended, chalicotheres’
hooves had been replaced with something new: claws. Now, claws on plant-eaters are pretty rare
– so rare, in fact, that the paleontologists who first found the feet of chalicotheres
thought they must have come from anteaters, or maybe giant pangolins. But we know now that chalicotheres were herbivores,
because their teeth bear the distinct scratches and pits that come from eating leaves, bark
and twigs. So instead of using their claws for digging,
these animals probably used them to get at the tastier leaves that were higher up in
the trees, a type of eating preference called high browsing. The claws may also have helped chalicotheres
stand on their hind legs and brace themselves against tree trunks, making it easier to browse. And they even had specialized neck vertebrae
that let them look up more easily than like a horse or a rhino. So, by about 40 million years ago, chalicotheres
had arrived at a single, pretty successful body plan, optimized for high browsing. But then, things started to get weird. Soon after the ancestral chalicotheres developed
claws, they began to follow different evolutionary paths. They started to evolve in parallel. One group of early chalicotheres got very
good at pulling leaves down to eat. So, over time, those animals with longer limbs
were more successful, until — about 30 million years ago — they all had big hulking arms,
long claws on their front legs, and necks much shorter than their ancestors’. And because of this new body plan, these animals
started walking with their front toes curled inward to protect their claws. They began walking on their knuckles! These animals became known as their own subfamily
of chalicotheres, called Chalicotheriinae. But meanwhile, a separate group of ancestral
chalicotheres started to develop its own adaptations for high browsing. Its early members were much better at nibbling
leaves right off the trees, without having to pull them down. Over time, those that were taller and had
longer necks were better at getting food, until eventually, they looked more and more
like long-necked horses. Or maybe, short-necked giraffes. And they still had claws, too. But all their legs were about the same size,
and these animals were bigger and heavier than their long-armed cousins. So, knuckle walking wasn’t an option for
them. Instead, they acquired the ability to retract
their claws. They had specialized tendons that helped them pull
their claws up while they walked, and the tendons were further strengthened by a fusion
of several bones in their toes. And, in many members of this group, domes
also appeared on their heads. No one’s exactly sure what purpose they
served, but the prevailing theories are that the animals used them for head-butting and
as a display to potential mates. As you do. And this group of long-necked, dome-headed
chalicotheres came to be known by the ungainly name of Shizerotheriinae. But, just like the other subfamily, they were
still chalicotheres! So if these two groups of animals lived in
the same area, why did they split at all? Why didn’t they keep evolving as one group,
ending up either as long-armed knuckle-walkers or long-necked horse-like dome head things? Well, that’s what makes parallel evolution
so interesting. It often occurs among closely-related animals,
even ones that share the same range. And in this case, it happened because both
body plans were equally likely to help an animal survive. So, early on, among the original, ancestral
chalicotheres, some variations appeared, which happens all the time in groups of organisms. Some chalicotheres had longer necks, and others
had longer forearms. But both differences helped ancestral chalicotheres
survive, reproduce, and ensure that their long-necked or long-armed traits were passed
on to the next generation. Slowly, over time, chalicotheres drifted apart,
until their differences were so extreme that they were different species – and then, different
subfamilies. But they both remained really good at doing
one thing: eating the tops of trees. Of course, as you know from the lack of them, their success didn’t last forever. Despite their specializations, chalicotheres
aren’t with us today. The last of both families died out in North
America 10 million years ago, and they lingered in Asia and Africa until about one million
years ago. One possible clue to their demise is the rise
of the artiodactyls — herbivores with four-chambered digestive systems, like deer, cattle, and
hippos. This digestive set-up is much more efficient
than the single-chamber system that chalicotheres had. So chalicotheres would have had to eat a lot
more to get the same nutrition that a giraffe, for example, could get with less food. And changes in climate wouldn’t have helped:
As Africa and large parts of Asia became drier, grasslands started to spread, reducing the
habitat of the tree-loving chalicotheres. Today, horses are rhinos remain their closest
living relatives. So, you can take the story of the chalicotheres
as proof of how versatile natural selection can be — how it can lead to many different
evolutionary solutions to a problem, all of which are equally successful. But you can also read this story as a lesson
in its limitations. I mean, if anything, chalicotheres turned
out to be too specialized. Each group became too good at high browsing
— to the point that, when the climate changed and competition pressure was on them, they
couldn’t survive. There are some situations that evolution just
can’t get you out of. Thanks to CuriosityStream for supporting PBS
Digital Studios. With CuriosityStream you can stream documentary
films, and programs about science, nature, and history, including exclusive originals! For example, you could check out Planet Dinosaur,
a three-part BBC series about the latest discoveries from the days of the non-avian dinos. CuriosityStream offers unlimited streaming,
and for Eons viewers the first two months are free
if you sign up at curiositystream.com/eons and use the promo code EONS. What do you want to know about the story of
life on Earth? You can let us know in the comments. And don’t forget to go to youtube.com/eons
and subscribe! And then go talk to all your friends and tell them to do it too [laughs]

How the Chalicothere Split In Two
Tagged on:                                                                                                                                     

100 thoughts on “How the Chalicothere Split In Two

  • November 17, 2018 at 2:41 am
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    https://naturalhistory2.si.edu/paleobiology/burgess/ this animal had also been a threat to trilobites and they were the ones who left the infamous 'W' shaped bite.

    Reply
  • November 18, 2018 at 10:08 pm
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    Could that dome on the head have been a resonator to amplify their calls?

    Reply
  • November 24, 2018 at 3:02 pm
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    Klingon horses maybe? 😜

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  • November 26, 2018 at 10:58 pm
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    These were beasts of burden in the time travel trilogy "The Saga of the Exiles". Great books set in the Pliocene

    Reply
  • November 27, 2018 at 7:52 pm
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    Eloi and Morloks…

    Reply
  • November 28, 2018 at 7:08 pm
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    you know this video is prove further that the rhynos are the supposed unicorns, horses relative with one corn.

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  • December 1, 2018 at 12:54 pm
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    Pachycephalosaurus horse lol xd😂😂😂😂

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  • December 5, 2018 at 2:56 am
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    Giraffidae next.

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  • December 15, 2018 at 1:58 am
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    Omg i love you guys. So great.

    Reply
  • December 23, 2018 at 11:03 am
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    I could watch 100 more videos on this type of evolution. So fascinating. 👍

    Reply
  • December 24, 2018 at 12:25 am
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    Planet Dinosaur is a 6 part series though.

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  • December 24, 2018 at 8:24 pm
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    The scary thing is that modern-day giraffes fit the niche left by the Chalicotheres, and are extremely specialized too. This means that if Africa dries up further, or grows weather, they'll be susceptible to environmental pressures and may not be able to survive. Same with pandas and koalas.

    Reply
  • December 31, 2018 at 12:59 pm
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    Could you do an episode about any relationship (or not) between the 12,000 year old meteor impact crater recently discovered in Greenland, and the extinctions of most of the megafauna, and also the Clovis culture, which also disappeared around the same time? My own understanding is that, lacking such an impact crater, the impact theory has rather languished; I'd love to see it re-examined in light of the discovery.

    Thanks for an interesting and informative series!

    Reply
  • December 31, 2018 at 7:57 pm
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    Does Pterodactyl mean “odd wing” then?

    Reply
  • January 1, 2019 at 6:59 am
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    Dang, so close to a more horse-like unicorn

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  • January 2, 2019 at 1:38 am
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    This is what happens when you forget to do “arms” at the gym

    Reply
  • January 6, 2019 at 12:09 am
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    I like this guy and Callie as hosts 😊

    Reply
  • January 6, 2019 at 8:59 pm
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    Im subscribed to 3 channels, Elite Dangerous (VR game/space sim), RailWay( for sleep, its a train just going), and now you guys. – I wanna learn about everything !!!!

    Reply
  • January 8, 2019 at 4:43 pm
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    Obviously the skull bulges are horn mounts.

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  • January 8, 2019 at 4:55 pm
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    does anyone knows which museum has the Chalicothere complete story?

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  • January 9, 2019 at 9:10 am
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    Shizzzaaaam! … otheriinae…

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  • January 10, 2019 at 3:50 pm
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    Wait horses and rhino's are from the same family!!!! You mean unicorns are real!!!

    Reply
  • January 11, 2019 at 12:36 pm
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    Im assembling an Ikea forniture and listening to these videos at the same time.
    Great experience.

    Reply
  • January 13, 2019 at 2:35 am
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    This channel is great!

    Reply
  • January 16, 2019 at 4:17 pm
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    Sorry, you made me confused here, Parallel evolution is not the aquisition of different traits for the same purpose (eating the top tree leaves) from a common ancestral state!!! this is wrong! that is a normal case of divergence! parallel evolution is the aquisition of similar traits (maybe for similar puposes) from the same ancestral state independently!!!
    https://www.sciencedaily.com/terms/parallel_evolution.htm
    see, examples in the link!

    Reply
  • January 17, 2019 at 8:39 pm
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    If these two animals lived in the same planes and areas, how come they didn’t breed with each other before their evolution branches off, hence halting the evolution process? You would think by being the same species in the same areas, they would be breeding with each other, therefore staying in the same species. Can anyone answer this for me?

    Reply
  • January 18, 2019 at 4:33 pm
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    I thought parallel evolution was what made unrelated animals look the same like hyenas and canines.

    Reply
  • January 19, 2019 at 2:17 am
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    Daamn nature you creative!! 😎

    Reply
  • January 19, 2019 at 2:18 am
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    Andsodon Grande looks like a giant buffed up hamster 😂

    Reply
  • January 26, 2019 at 4:45 pm
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    Migrated here from TierZoo 🙂

    Reply
  • January 26, 2019 at 11:41 pm
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    These chacilotheres look like something you'd find from a scifi-fantasy game. Too bad they don't exist anymore. They are weirdly cute.

    Reply
  • January 31, 2019 at 4:06 pm
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    how come all these animals even dinosaurs are not explained or have any proof from our ancestors but we got drawing and artifacts of dragons from every culture and bibles and medieval time. hmmm

    Reply
  • February 5, 2019 at 7:33 am
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    So much science

    Reply
  • February 7, 2019 at 9:53 pm
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    question, how does nature create two body plans originating from one species when both 'potential good body plans" still have opportunity to mate with eachother?

    Reply
  • February 8, 2019 at 10:08 pm
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    Ark🦍

    Reply
  • February 10, 2019 at 9:30 pm
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    More proof unicorns used to exist

    Reply
  • February 12, 2019 at 11:30 pm
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    can it throw boulders?

    (ARK: Survival Evolved reference

    Reply
  • February 13, 2019 at 3:43 pm
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    So Parallel Evolution in todays time would be an example of Polar bears and Brown Bears? Or ?

    Reply
  • March 2, 2019 at 7:59 am
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    How about Pleistocene species that may have survived slightly beyond 10,000 years ago?

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  • March 2, 2019 at 2:09 pm
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    Is BoJack Horseman a descendant of Chalicotherium

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  • March 3, 2019 at 5:50 am
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    But one question not answered by this video is how the early differences weren't wiped out by interbreeding.

    Reply
  • March 4, 2019 at 4:10 am
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    Lmao that ending😂

    Reply
  • March 5, 2019 at 4:17 am
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    The Dome head seemed like it would be for knocking fruit off trees or fighting

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  • March 11, 2019 at 1:24 am
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    Does any other animal species have what we would call races?

    Reply
  • March 11, 2019 at 3:01 am
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    Hey, talking about trees… what about tree evolution ?! That'd be a great topic for one (or a few) new amazing videos 🙂

    Reply
  • March 11, 2019 at 5:33 am
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    I enjoyed this video but I think you missed a credit for Jay Matternes whose illustrations are featured at least twice (1:49 and 5:29).

    Reply
  • March 13, 2019 at 7:49 am
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    I've always found Chalicothere's fascinating, so thank you so much for making this video! I learnt so much from it.

    Reply
  • March 14, 2019 at 9:00 am
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    I'm here cause of the game ark survival 😅
    Favorite tame by far, but I always called pronounced it like
    kal ic O th or e um

    Reply
  • March 15, 2019 at 1:55 pm
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    A hard bone dome on your crown would help you slam nuts out of trees… Like pecan and olive trees that need a good jostle.

    Reply
  • March 16, 2019 at 3:10 am
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    A Californian Chalicothere eating cauliflower and doing calligraphy.

    Reply
  • March 16, 2019 at 5:37 am
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    A THEORY called parallel evolution

    Reply
  • March 16, 2019 at 2:36 pm
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    Therizinosaurus 2.0

    Reply
  • March 18, 2019 at 11:25 am
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    I love how the massive bumps on those rhino-horsey's foreheads formed because they thought headbutting each other to the death was the best way to figure out who gets all the ladies

    Reply
  • March 18, 2019 at 2:14 pm
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    Excellent video!

    Reply
  • March 22, 2019 at 4:48 pm
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    would love more videos about Paleobotany 🙂

    Reply
  • March 29, 2019 at 9:26 am
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    Does an 'Urbivore' eat towns and cities?

    Reply
  • April 2, 2019 at 9:43 pm
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    It’s not (ka-li-ko-th-ee-r) it’s (chal-ii-ko-theer)

    Reply
  • April 16, 2019 at 9:15 pm
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    As why they split in two –
    may be due to difference in food preference. The long armed version may have found some difficulty in pulling down branches from stiff trees like big oaks and pine/ spruce species. Long-arm probably preferred easier flexible stuff like willow elder and birch, where it could devour leaves up to a higher level than the long necked horse which couldn't pull down branches. But horse nibble browser probably had less problems with the stiffer leaves on rigid branches like grown beeches oaks and spruce.

    So the long necked horse may have strayed to adult forests with bigger trees, whereas the long armed may have liked the younger forests with willow birch and young oaks. Last type tends to be pioneer vegetation after forest fires and in flood areas (an extreme flood can clear a good part of a plain from forests) whereas hard-wood species are found in older forests with less natural disturbance. Though I reckon both chalicothere types would have had a harder time in virgin forest where most branches are too high and rigid for the even the longest necks and arms.

    Would be easy too check since their teeth will differ accordingly – as will the tree species in deposits where those teeth are found 😛

    Reply
  • April 17, 2019 at 8:14 pm
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    Therapist: gorilla horses aren't real they can't hurt you

    Gorilla horses:

    Reply
  • April 23, 2019 at 1:10 pm
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    🐧 video

    Reply
  • May 13, 2019 at 6:28 pm
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    One thing you might have mentioned in addition is that animals may tend to diversify into specialized niches more when there is greater competition ie a great abundance of animals may create greater evolutionary pressure to diversify. great presentation thank you

    Reply
  • May 15, 2019 at 6:09 am
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    Pbs is so underrated. You can learn so much.

    Reply
  • May 15, 2019 at 9:49 pm
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    I’m sorry kid, but this video is ridiculous

    Reply
  • May 19, 2019 at 11:39 pm
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    It's SCHIZOTHERIINAE, not Shizerotheriinae.

    Reply
  • May 22, 2019 at 9:52 pm
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    Evolution of mammals during the current human life span?

    Reply
  • May 22, 2019 at 11:05 pm
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    4:28 – Maybe the dome was for banging the tree to shake fruit loose

    Reply
  • May 23, 2019 at 7:40 pm
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    where is that painting at 1:49 from?

    Reply
  • May 31, 2019 at 8:28 pm
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    Chalicotherinae looks like it has a job as club security.

    Reply
  • June 5, 2019 at 4:34 pm
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    “Long neck dome headed” go easy on them damn

    Reply
  • June 6, 2019 at 11:46 am
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    That something walking on its knuckles? Keep on …ing. well. Whatever the hell that thing is, it looks so anatomically wrong. Looks like some retards in special needs school drew that.

    Reply
  • June 8, 2019 at 6:46 am
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    Anyone here play ark and hate when those chalicos throw poop at you

    Reply
  • June 9, 2019 at 7:59 pm
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    High-browsing became too high-brow….sing the portly lady then did about their failed experiment in erudition nutrition.

    Reply
  • June 11, 2019 at 4:52 am
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    You left me hanging in the end as to why the Chalicotheres went extinct. Did trees lose their high leaves?

    Reply
  • June 11, 2019 at 12:53 pm
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    Thank you for the video Imani like how you explain things The evolution of Fungi and mushrooms and everything from the beginning to today.
    Please lol thank you

    Reply
  • June 12, 2019 at 6:24 pm
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    But why didn't they keep interbreeding? Did mixes of both qualities die more often which forced animals to look alike to breed together? Or is it in their instinct to breed with an individual that looks more like them?
    Because if both were equally succesfull and they lived next to eachother then why didn't they just keep interbreeding with one another?

    Reply
  • June 13, 2019 at 8:09 pm
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    It is fascinating to think that animals have fetish-like preferences during parallel evolution. They showed a preference for what seems a superficial trait and it resembles how we often select our partners for similar reasons. Take those humans who fetishize skin colour (or as we socially call them racial fetishes), seems superficial but actually improves genetic variation in the shallower gene pools outside Africa.

    Reply
  • June 14, 2019 at 5:02 pm
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    In layman's terms, one is lazy, the other wasn't

    Reply
  • June 15, 2019 at 8:38 am
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    Couldn't the dome be used to headbutt trees to shake lose leafs?

    Reply
  • June 16, 2019 at 9:52 am
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    Came here from TierZoo, anybody else?

    Reply
  • June 16, 2019 at 4:19 pm
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    I love these videos and you're great Hank, but you did an amateurish mistake here, sorry! What you are talking about is not what evolutionary biologists would call parallel evolution, but divergent evolution.
    Parallel evolution is essentially the same to convergent evolution ( = different taxa evolve similar traits independently), but in closely related taxa rather than in distantly related ones. Confusing, I know… So much that some biologists suggest to drop the terminological distinction and just call it convergent evolution, https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(07)00287-X

    Reply
  • June 18, 2019 at 8:10 pm
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    0:14–0:23 that slightly disturbing 'has the face of a horse, does not have the body of a horse'

    Reply
  • June 19, 2019 at 5:54 am
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    What if the Mystery of Desmostylians?

    Reply
  • June 19, 2019 at 12:25 pm
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    Who was the cause of the climate change back then or did somehow man have something to do with them dying off to

    Reply
  • June 20, 2019 at 1:55 pm
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    The pre Horse, Giraffe, etc. With claws! Roar! Herbavor toughness!

    Reply
  • July 6, 2019 at 7:28 pm
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    I can't stand this guy.

    Reply
  • July 7, 2019 at 7:49 pm
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    These things always attack me when I get close..i mean I was just farming wood and it goes aggro on me

    Reply
  • July 12, 2019 at 9:05 pm
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    Great channel. U guys give very detailed info. Anything dealing specifically with the Mesozoic era, n all other prehistoric periods I find absolutely fascinating. 🦖🦕

    Reply
  • July 14, 2019 at 1:36 pm
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    Giraffeey neck😁

    Reply
  • July 14, 2019 at 1:40 pm
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    Fascinating world. Thanks.

    Reply
  • July 24, 2019 at 7:31 am
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    We are witnessing the split of two branches of the same specie, chihuahua dogs and Great Danes are having a hard time mating… eventually they may become two different species, and if they do, then both will have the same common ancestor named "dog".

    Reply
  • July 25, 2019 at 9:52 pm
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    Why didn`t they just sprout wings and a long tail?

    Reply
  • July 25, 2019 at 10:48 pm
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    So in this case the new species showed up without being isolated on small island or continent,without incesr happening in the early stages,so one might say that each individual had different percentage of genes combined.

    Reply
  • July 29, 2019 at 1:48 am
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    This is like the Digimon phases

    Reply
  • July 31, 2019 at 7:27 pm
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    I am going to look for traits of calicothere in my horse 😂

    Reply
  • August 1, 2019 at 4:34 am
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    easy, that one is from alola and that one isnt

    Reply
  • August 4, 2019 at 5:34 pm
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    Could they've digged up treeroots to eat?

    Reply
  • August 17, 2019 at 3:21 pm
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    Make sure to bring beer when taming.

    Reply
  • August 18, 2019 at 1:48 am
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    You: Chalicotherium
    Me, an intellectual: Donkey Kong

    Reply
  • August 21, 2019 at 7:40 pm
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    My course has been crashed

    Reply
  • August 22, 2019 at 12:02 am
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    Disclaimer:

    All of this is a Theory and NOT 100% proven.

    UNFILTERED UNAPOLOGETIC TRUTH 🇺🇸

    Reply

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