The Raptor That Made Us Rethink Dinosaurs

The Raptor That Made Us Rethink Dinosaurs

In 1964, a paleontologist named John Ostrom
dug up some fascinating fossils from the mudstone of Montana. The fossils were of a slim, sleek dinosaur
with sharp, curved claws on its feet, and a long tail supported by tendons that allowed
it to work like a rudder. From the evidence, Ostrom could tell that
this new dinosaur was an active, agile predator. But that was totally at odds with popular
interpretations of dinosaurs at the time, which was that they were all slow, dumb, lumbering
beasts. This revolutionary discovery was given the
name Deinonychus, or “terrible claw,” and Ostrom’s description of it set the stage
for what’s known today as the D inosaur Renaissance, a total re-thinking of what we thought we
knew about dinosaurs. And one of the key questions that scientists
revisited was whether dinosaurs were warm-blooded or cold-blooded. For decades, paleontologists have been studying
this question six ways from sunday, attacking it from every angle. And so far, the answer seems to be: They were
both warm blooded and cold blooded. But also: neither. And also also: Maybe that’s not even the right
question to ask. Because the fact is, almost 50 years after
the Dinosaur Renaissance began, this one fundamental function of dinosaurs’ bodies — their metabolism
— remains mysterious to us. But what we have learned about dinosaurs’
metabolism is that it was probably diverse, and  experts are starting to think that maybe
it’s not a question of either/or, yes or no, hot or cold. The clues we have are conflicting, and fascinating,
and surprising. And they can tell us a lot, not just about
how strangely diverse dinosaurs were, but also about the evolution of modern birds,
and maybe even why the non-avian dinosaurs are no longer with us. You’ve probably heard of metabolism as a
kind of short-hand for how many calories your body uses to keep you alive. But more accurately, metabolism refers to
all of the chemical reactions that go on inside an organism, like the ones that convert food
into energy, and the ones that build compounds that its cells need. These chemical reactions also produce heat. And warm-blooded animals use this heat in
what’s known as endothermy. Endotherms can make enough heat that they
often don’t need to rely on their environment to stay warm. This sets them apart from ectotherms, or so-called
cold-blooded animals – like most fish, reptiles, amphibians, and invertebrates. They mainly rely on their environment to set
their body temperature. This difference in temperature-regulation
means that endotherms can live in more variable environments and are usually more active than
ectotherms. So figuring out if an animal is warm- or cold-blooded
can tell us a lot about how it lived, which is why experts have been puzzling for so long
over which ones the dinosaurs were. And in the early days of dinosaur paleontology,
people mostly thought dinosaurs were just big lizards and lived the same basic life
as your average iguana. In fact, the first dinosaur named was Megalosaurus,
the “Great Lizard.” Based on its fossils, including a partial
jaw and thighbone, naturalist William Buckland described it in 1824 as a huge lizard that
was probably amphibious. Within a decade of that find, two more prehistoric
reptiles were described – the duck-billed Iguanodon and armoured Hylaeosaurus. And together these finds prompted paleontologist
Sir Richard Owen in 1841 to propose the clade Dinosauria, or the “terrible lizards”. But then in the 1870s, a new discovery challenged
the idea of dinosaurs as plodding, simple beasts. It was the discovery of Archaeopteryx. Archaeopteryx belonged to a lineage of flying
dinosaurs, called Avialae that sits between feathered theropods, like
Deinonychus, and modern birds. It had some distinctly bird-like traits, like
a wishbone, wings, and flight feathers, and it could probably fly at least a little. But it also looked a lot like other dinosaurs:
It had sharp teeth, three clawed fingers, and a long bony tail. And its ankles and wrists were also distinctly
theropod-like. The discovery of Archaeopteryx was the first
indication that dinosaurs were more than oversized lizards: They also seemed to be active animals
that might have been related to birds. But these ideas didn’t really take hold
until John Ostrom resurrected them in the 1970s, when he described Deinonychus as a
bigger version of Archaeopteryx. He argued that birds descended from dinosaurs,
and that many features associated with birds — active lifestyles, agility, and most importantly,
endothermy — got their start in an ancient creature that probably looked like Deinonychus. Ostrom’s ideas fundamentally challenged
our understanding of dinosaurs. And because of that, Deinonychus may be one
of the most important dinosaur fossils ever discovered. But Ostrom’s initial argument was based
on the bigger general features of Deinonychus. With the development of new, sophisticated
tools, paleontologists became able to examine fossils down at the microscopic level. And this gave experts a tremendous amount
of new information! But still, in many cases, the evidence has
been either inconclusive or conflicting. For example, as early as the 1960s, researchers
began studying bone tissue. Typically, fast-growing, active endotherms
have a type of bone tissue called fibrolamellar bone. This type of bone grows really quickly, and
it looks kind of woven, like fabric. It’s also dotted with features known as
Haversian canals, which are the pathways the blood vessels followed to bring nutrients
to the fast-growing tissue. By contrast, the bones of ectotherms grow
more slowly and have fewer of these canals. And they’re also lined with dark rings that
show when the bone growth slowed down, which happens in cold-blooded animals during times
of seasonal stress. So what do dinosaur bones look like? Do they have the woven pattern, or rings? Well, some dinosaur bones have lots of weaves,
and some have lots of rings. Deinonychus, for example, has no bone rings,
and was probably more like an endotherm. Archaeopteryx, on the other hand, did have
rings, indicating that it was slow-growing and was probably more of an ectotherm. So some dinosaurs appear to have endothermic
traits, while others have signs of being ectothermic. But getting mixed results from bone tissue
is not unheard-of: Fibrolamellar bone has been found in animals that we know are cold-blooded,
like young alligators. And rings of slow growth also appear in some
modern warm-blooded animals, like deer. So another way to learn about dinosaurs’
metabolism is to look for anatomical features in their fossils that we know are related
to endothermy. For example, mammals and birds both have noses
that are lined with features known as respiratory turbinates. These are little webs of bony tissue that
warm up air that’s entering the lungs and remove moisture from the breath as it’s
being exhaled. It’s an adaptation that helps us, and other
endotherms, retain more heat and water during respiration. So finding respiratory turbinates in a skull
is widely considered to be evidence of endothermy. And in the 1990s, researchers studied the
nasal regions of three species of theropods and one ornithischian. They found that, in all cases, the nasal passages
were too narrow to have respiratory turbinates and instead they more closely resembled those
of ectotherms. But! Because nothing is straightforward on this
topic! In 2014, researchers reported what seemed
to be  respiratory turbinates in fossils of pachycephalosaurids from North America
and Mongolia. And in 2018, similar nasal structures in two
different species of ankylosaurs were shown to have functioned like turbinates. Now, other scientists have used lots of other
lines of evidence to answer the same question, like trying to estimate dinosaurs’ blood
pressure, brain size, predator to prey ratios, and other things. But those investigations have all also produced
mixed results. So it seems that some dinosaurs were so active
that they probably ran a little bit warm, even if they were otherwise cold-blooded. And we know that this is at least possible,
because that’s how some fish live — like modern tunas and lamnid sharks. These animals use a sophisticated network
of blood vessels to keep the heat generated from their working muscles inside their bodies,
instead of losing it to the cold ocean waters around them. So even though most animals today are either
one or the other, dinosaurs were probably somewhere in between – some dinosaurs were
more ectothermic, while others were more endothermic. Animals like this, that control their body
temperature in a variety of ways, are mesothermic, and today they’re pretty rare. But of course, I’ve just been talking about
the extinct dinosaurs — the non-avian dinosaurs. What complicates this picture even more is
the fact that avian dinosaurs — aka birds — are all warm blooded. So how did this switch happen? How did a group of animals completely reorganize
its physiology to go from mesothermic to endothermic? Well, modern birds can tell us some interesting
things about the origins of endothermy. Think of a baby bird. When it hatches, it’s naked and depends
on its parents for warmth. It’s basically a little ectotherm. But as chicks develop, their tissues start
producing more energy through the mitochondria in their cells. As a result, the mitochondria give off more
heat. It becomes an endotherm. Now, we don’t really understand what causes
their mitochondria to kick into high gear. But experts think it may one day tell us a
lot about what mechanisms could be at play in the evolution of endothermy. We do, at least, have a sense of when endothermy
evolved in birds. The fossil record shows that, in the mid-Cretaceous
Period, birds had respiratory turbinates, as you’d expect in animals with a very high
metabolism needed for flight. And by the late Cretaceous, birds were fully
endothermic. And not a moment too soon. Stop me if you’ve heard this before but 66 million years ago, a combination of volcanic
activity and a massive asteroid impact set off a global catastrophe of dust, acid rain,
and cold. At least 75% of all species on Earth vanished,
including all non-avian dinosaurs. But the ancestors of the modern birds survived. Warm-blooded birds could stay active even
as the climate took a turn for the worse, and even though they were endotherms, they
needed much smaller amounts and different kinds of food than the huge dinosaurs did. Out of the ashes of the extinction event,
the avian dinosaurs rose and filled many of the niches left vacant by their more reptilian
cousins. So sometimes unearthing a revolutionary fossil
like Deinonychus solves a mystery. But more often than not, it brings up more
questions. But the questions themselves are incredibly
valuable. Because they remind us that there’s a lot
more to these terrible lizards than we once thought. As always a big thanks to this month’s Eontologists:
Patrick Seifert, Jake Hart, Jon Davison Ng, and my boy Steve! Now if go to and make a pledge of
$15 or more to get access to our new quarterly Eons livestream! You’ll get insider updates about the show,
as well as the latest paleo news, and special guests! And also thank YOU for joining me today, in
the Konstantin Haase Studio, if you haven’t already go to and subscribe.

100 Replies to “The Raptor That Made Us Rethink Dinosaurs”

  1. If the dinosaurs became extinct, how could modern birds (or any other creature for that matter) have evolved from them ?

  2. And yet we still see these sort of dinosaurs in media shown as having smooth or scaly skin, not feathered…

    I don't know about you guys but having feathers would actually make things cooler onscreen/ingame….

  3. Isnt the smaller version of the flying type just the younger but same species, where are the bone density studies on these dinos.

  4. Fan of all your episodes but this one needs more time. Please make a follow up episode cause its very interesting

  5. Let ask a video on the evolution of viviparity (development of the embryo inside the body of the parents). Please upvote if you agree

  6. thanks for sharing this awesome video it sure tight me something i never thought of and by the way i even modeled Deinonychus in blender

  7. Hey Eons! I want to know more about the groups of mammals that evolved isolated in South America. The notoungulates, liptopterns, and all the others seem to always be brushed over in the story of life.

  8. Can you do a video about global warming and what would happen if we let it go on without infering? How would the coastlines look like and how would the surface of earth Change(dessert and forests etc.)?

  9. Anyone else want to learn more about how paleontologists used to think of dinosaurs vs what we know now?

  10. It just sucks to think how dinosaurs would feel if they ever get resurrected only to find out that we have labeled them as terrible

  11. Wait, 66 MYA? Since when was it 66? It was always 65 when I was growing up, and people lately have been saying 65.5 instead. When did it become 66? Has it really been that long since my childhood that it needed to be updated?

  12. bone growth aspect of ectothermic modern alligators may be explained by new thoughts/evidence that some ancestral/ancient crocodiles were endothermic.

  13. How come we don't know all had scales but we assume that thou their is alot of evidence to show moat has feathers

  14. I feel like if science ever reaches a point where we can reliably ressurect one of these extinct species, we should do so. In a controlled purely scientific enviroment of course. No Jurassic Park. It could for example allow us to better understand how evolution works. Find out their nature, and it'd show we can do incredible things.

  15. Paleontologist: So you guys are more related to birds than reptiles?

    Deinonychus: That’s correct Mary, in fact we all wear masks sometimes!

  16. I wish the Tyrannosaurus were still alive today so i can take them as my house pet. I will feed them myself with my own bare hands. 😆

  17. If we say that the meteor that hit the earth, somehow changed out air to be the very same air we breathe today, what if the dinosaurs couldn't breathe our air? What if some dinosaurs survived and evolved into animals we know today? What if dinosaurs evolved to breathing our air? I could keep going on this.

  18. No one complaining about the mistake at about 2 minutes? Color me surprised, normally the internet is much less forgiving. I am almost positive he accidentally said endotherm when he meant ectotherm

  19. could yall consider doing a video on sex and gender in some prehistoric animals and how they may not have been binary?

    like, in modern times, there are many animals with sex/gender traits that are considered not strictly male or female (bees, ants, self-cloning lizards, clownfish, etc), or that have unusual traits for said gender (hyena, some birds with different kinds of males, maned lionesses, etc). it would be really interesting to learn about what science can tell about this kind of thing in prehistoric animals!

    thanks for reading

  20. You should absolutely do a video on the common ancestor of bears, cat, and dogs! I've been curious about that

  21. I wonder if you guys can do the evolution of some known animals? Go through all their known predecessor and how they became the way they are now.

  22. This reminds me of when I was in high school, and I asked my Biology teacher how birds are warm-blooded if dinosaurs were cold-blooded. He told me that they developed warm-blood, and needed to in order to have enough energy for flight. I asked if dragons would need to be warm-blooded to fly. He told me they probably would. I asked him if they would resemble birds more than lizards or snakes, and he said he thinks that would make more sense, too. So, my fellow nerds, may I propose the idea of dRaGoNs WiTh FeAtHeRs?

  23. Fascinating! You handle all these complicated questions SO very well, it's never ever boring!

    I'm wondering – I believe you already covered the evolution of horses, yes? But can we take a look at the evolution of the "other" hooved critters of the world – goats, deer, and so forth?

  24. Could you do a segment on the carnivoran families Nimravidae and Barbourofelidae. Particularly when they first evolved and when they died out. I'm getting too many conflicting dates and would like to have a definitive answer. I'd also like to know if the rise of sabre-toothed felids played a role in their extinction.

  25. Do a video on cryptids such as bigfoot and whether there is even a justification for their existence. I know I'm asking for something much different from the main course on the channel.

  26. Many of the large one were probably gigantotherms.
    You don't need specific metabolic adaptations to generate internal heat when it's so hard to lose it in the first place.

  27. please, guys.. i know it's usually boring but can u make a reminder, even writen to like the video at the begining of it? I watch all of your videos and love em' all but i keep forgetting to do, so. I believe it's not just me, so… Danke!

  28. Here is an idea for a video. A longer video explaining how most dinosaurs had feathers, from theropods to raptors and mist likely T. rex. You can present the evidence supporting this and clear up some misconsceptions

  29. This is gonna sound like a weird request. But my two year old loves watching these videos with me. He loves the dinosaur and cat episodes. But he also loves cows. We just watched the horse one and he loved it! So is there any interesting history of cows that I can show or read to him?

  30. Is there such thing as a reconverging branch genus like if a genus splits into two different genus’s but reconvenes due to circumstances?

  31. I would like to know about any correlations or any direct relations between polar reversals to species in fossil record (up to current), and the potential implications … ?

  32. Another great video guys. Any chance you could do something about the ancient oceans like Iapetus? Or something about the british isles (particularly Ireland ) and the caledonian orogeny thanks

  33. Wait, if dinosaurs were birdike than lizards and prerosaurs were flying reptiles, why aren't birds evolved from pterosaurs instead.

  34. Whenever I watch videos like this I think it sucks that we'll never see one of these animals in the flesh and all we have is fossils and guesses.

    Even if they manage to clone one they can only use animals we have today so it will never be an exact replica

  35. i have a question for anyone who might know why:
    why havent museums and stuff added feathers to their dinosaur exhibits where we know there are feathers? since i was a kid ive always loved day trips to natural science museums and stuff like that and havent gone for a really long time. i went to a museum a few weeks ago and in the dinosaur exhibits there were no mentions of feathers or even feathers being up for debate on some kinds. do you think its a money thing (as in itd cost too much money to make new models, signs, etc) or do you think it might just be an "everyone likes these ones so lets not change it" thing?

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