WEBVTT

00:00:01.016 --> 00:00:03.444
We've all heard about
how the dinosaurs died.

00:00:04.285 --> 00:00:06.238
The story I'm going to tell you

00:00:06.262 --> 00:00:10.874
happened over 200 million years
before the dinosaurs went extinct.

00:00:11.481 --> 00:00:14.367
This story starts at the very beginning,

00:00:14.391 --> 00:00:16.736
when dinosaurs were just
getting their start.

00:00:17.269 --> 00:00:19.994
One of the biggest mysteries
in evolutionary biology

00:00:20.018 --> 00:00:23.032
is why dinosaurs were so successful.

00:00:23.548 --> 00:00:27.307
What led to their global dominance
for so many years?

00:00:27.896 --> 00:00:31.414
When people think about
why dinosaurs were so amazing,

00:00:31.438 --> 00:00:35.243
they usually think about the biggest
or the smallest dinosaur,

00:00:35.267 --> 00:00:36.712
or who was the fastest,

00:00:36.736 --> 00:00:38.304
or who had the most feathers,

00:00:38.328 --> 00:00:41.234
the most ridiculous armor,
spikes or teeth.

00:00:42.126 --> 00:00:46.110
But perhaps the answer had to do
with their internal anatomy --

00:00:46.134 --> 00:00:48.326
a secret weapon, so to speak.

00:00:48.716 --> 00:00:52.423
My colleagues and I,
we think it was their lungs.

NOTE Paragraph

00:00:53.149 --> 00:00:57.403
I am both a paleontologist
and a comparative anatomist,

00:00:57.427 --> 00:00:59.372
and I am interested in understanding

00:00:59.396 --> 00:01:02.805
how the specialized dinosaur lung
helped them take over the planet.

00:01:03.797 --> 00:01:07.498
So we are going to jump back
over 200 million years

00:01:07.522 --> 00:01:09.275
to the Triassic period.

00:01:09.299 --> 00:01:11.691
The environment was extremely harsh,

00:01:11.715 --> 00:01:13.355
there were no flowering plants,

00:01:13.379 --> 00:01:15.634
so this means that there was no grass.

00:01:15.658 --> 00:01:20.056
So imagine a landscape
filled with all pine trees and ferns.

00:01:20.587 --> 00:01:24.040
At the same time,
there were small lizards,

00:01:24.064 --> 00:01:26.455
mammals, insects,

00:01:26.479 --> 00:01:30.793
and there were also carnivorous
and herbivorous reptiles --

00:01:30.817 --> 00:01:33.104
all competing for the same resources.

NOTE Paragraph

00:01:33.454 --> 00:01:34.995
Critical to this story

00:01:35.019 --> 00:01:40.347
is that oxygen levels have been estimated
to have been as low as 15 percent,

00:01:40.371 --> 00:01:42.524
compared to today's 21 percent.

00:01:42.932 --> 00:01:46.519
So it would have been crucial
for dinosaurs to be able to breathe

00:01:46.543 --> 00:01:48.418
in this low-oxygen environment,

00:01:48.442 --> 00:01:50.297
not only to survive

00:01:50.321 --> 00:01:53.010
but to thrive and to diversify.

NOTE Paragraph

00:01:54.462 --> 00:01:57.559
So, how do we know
what dinosaur lungs were even like,

00:01:57.583 --> 00:02:02.716
since all that remains of a dinosaur
generally is its fossilized skeleton?

00:02:03.257 --> 00:02:08.349
The method that we use is called
"extant phylogenetic bracketing."

00:02:09.085 --> 00:02:13.130
This is a fancy way of saying
that we study the anatomy --

00:02:13.154 --> 00:02:16.730
specifically in this case,
the lungs and skeleton --

00:02:16.754 --> 00:02:20.732
of the living descendants of dinosaurs
on the evolutionary tree.

00:02:21.235 --> 00:02:24.199
So we would look at the anatomy of birds,

00:02:24.223 --> 00:02:27.081
who are the direct
descendants of dinosaurs,

00:02:27.105 --> 00:02:29.454
and we'd look at
the anatomy of crocodilians,

00:02:29.478 --> 00:02:31.426
who are their closest living relatives,

00:02:31.450 --> 00:02:34.443
and then we would look at
the anatomy of lizards and turtles,

00:02:34.467 --> 00:02:37.072
who we can think of like their cousins.

00:02:37.096 --> 00:02:40.532
And then we apply these anatomical data
to the fossil record,

00:02:40.556 --> 00:02:44.199
and then we can use that
to reconstruct the lungs of dinosaurs.

00:02:44.223 --> 00:02:46.267
And in this specific instance,

00:02:46.291 --> 00:02:51.205
the skeleton of dinosaurs most closely
resembles that of modern birds.

NOTE Paragraph

00:02:51.696 --> 00:02:56.462
So, because dinosaurs were competing with
early mammals during this time period,

00:02:56.486 --> 00:03:00.145
it's important to understand
the basic blueprint of the mammalian lung.

00:03:00.597 --> 00:03:03.431
Also, to reintroduce you
to lungs in general,

00:03:03.455 --> 00:03:06.090
we will use my dog Mila of Troy,

00:03:06.114 --> 00:03:08.154
the face that launched a thousand treats,

00:03:08.178 --> 00:03:09.397
as our model.

NOTE Paragraph

00:03:09.421 --> 00:03:11.004
(Laughter)

NOTE Paragraph

00:03:11.028 --> 00:03:14.764
This story takes place
inside of a chest cavity.

00:03:14.788 --> 00:03:17.985
So I want you to visualize
the ribcage of a dog.

00:03:18.009 --> 00:03:20.466
Think about how
the spinal vertebral column

00:03:20.490 --> 00:03:23.759
is completely horizontal to the ground.

00:03:23.783 --> 00:03:26.358
This is how the spinal
vertebral column is going to be

00:03:26.382 --> 00:03:28.788
in all of the animals
that we'll be talking about,

00:03:28.812 --> 00:03:30.310
whether they walked on two legs

00:03:30.334 --> 00:03:31.487
or four legs.

NOTE Paragraph

00:03:31.511 --> 00:03:36.025
Now I want you to climb inside
of the imaginary ribcage and look up.

00:03:36.944 --> 00:03:39.019
This is our thoracic ceiling.

00:03:39.480 --> 00:03:43.399
This is where the top surface of the lungs
comes into direct contact

00:03:43.423 --> 00:03:45.748
with the ribs and vertebrae.

00:03:46.374 --> 00:03:49.863
This interface is where
our story takes place.

00:03:50.398 --> 00:03:53.433
Now I want you to visualize
the lungs of a dog.

00:03:53.457 --> 00:03:56.645
On the outside, it's like
a giant inflatable bag

00:03:56.669 --> 00:04:00.080
where all parts of the bag
expand during inhalation

00:04:00.104 --> 00:04:02.577
and contract during exhalation.

00:04:02.601 --> 00:04:05.878
Inside of the bag, there's a series
of branching tubes,

00:04:05.902 --> 00:04:08.385
and these tubes are called
the bronchial tree.

00:04:08.899 --> 00:04:15.014
These tubes deliver the inhaled oxygen
to, ultimately, the alveolus.

00:04:15.038 --> 00:04:20.080
They cross over a thin membrane
into the bloodstream by diffusion.

NOTE Paragraph

00:04:20.572 --> 00:04:22.750
Now, this part is critical.

00:04:23.440 --> 00:04:26.925
The entire mammalian lung is mobile.

00:04:26.949 --> 00:04:31.967
That means it's moving
during the entire respiratory process,

00:04:31.991 --> 00:04:34.577
so that thin membrane,
the blood-gas barrier,

00:04:34.601 --> 00:04:37.636
cannot be too thin or it will break.

00:04:37.660 --> 00:04:41.202
Now, remember the blood-gas barrier,
because we will be returning to this.

NOTE Paragraph

00:04:41.721 --> 00:04:43.206
So, you're still with me?

00:04:43.230 --> 00:04:45.858
Because we're going to start birds
and it gets crazy,

00:04:45.882 --> 00:04:47.322
so hold on to your butts.

00:04:47.346 --> 00:04:48.951
(Laughter)

00:04:49.648 --> 00:04:52.903
The bird is completely different
from the mammal.

00:04:53.495 --> 00:04:55.888
And we are going to be
using birds as our model

00:04:55.912 --> 00:04:58.343
to reconstruct the lungs of dinosaurs.

NOTE Paragraph

00:04:58.367 --> 00:04:59.931
So in the bird,

00:04:59.955 --> 00:05:04.172
air passes through the lung,
but the lung does not expand or contract.

00:05:04.707 --> 00:05:06.648
The lung is immobilized,

00:05:06.672 --> 00:05:08.964
it has the texture of a dense sponge

00:05:08.988 --> 00:05:14.195
and it's inflexible and locked into place
on the top and sides by the ribcage

00:05:14.219 --> 00:05:17.313
and on the bottom
by a horizontal membrane.

00:05:18.300 --> 00:05:21.386
It is then unidirectionally ventilated

00:05:21.410 --> 00:05:25.398
by a series of flexible,
bag-like structures

00:05:25.422 --> 00:05:28.210
that branch off of the bronchial tree,

00:05:28.234 --> 00:05:29.822
beyond the lung itself,

00:05:29.846 --> 00:05:31.716
and these are called air sacs.

NOTE Paragraph

00:05:32.249 --> 00:05:37.607
Now, this entire extremely delicate setup
is locked into place

00:05:37.631 --> 00:05:40.820
by a series of forked ribs

00:05:40.844 --> 00:05:43.549
all along the thoracic ceiling.

00:05:43.573 --> 00:05:46.655
Also, in many species of birds,

00:05:46.679 --> 00:05:49.103
extensions arise from the lung

00:05:49.127 --> 00:05:50.673
and the air sacs,

00:05:50.697 --> 00:05:53.305
they invade the skeletal tissues --

00:05:53.329 --> 00:05:56.031
usually the vertebrae,
sometimes the ribs --

00:05:56.055 --> 00:05:59.014
and they lock the respiratory
system into place.

00:05:59.038 --> 00:06:02.474
And this is called
"vertebral pneumaticity."

00:06:02.498 --> 00:06:05.740
The forked ribs and
the vertebral pneumaticity

00:06:05.764 --> 00:06:09.281
are two clues that we can hunt for
in the fossil record,

00:06:09.305 --> 00:06:11.894
because these two skeletal traits

00:06:11.918 --> 00:06:16.637
would indicate that regions
of the respiratory system of dinosaurs

00:06:16.661 --> 00:06:18.335
are immobilized.

NOTE Paragraph

00:06:21.200 --> 00:06:23.806
This anchoring of the respiratory system

00:06:23.830 --> 00:06:27.737
facilitated the evolution
of the thinning of the blood-gas barrier,

00:06:27.761 --> 00:06:33.860
that thin membrane over which oxygen
was diffusing into the bloodstream.

00:06:34.746 --> 00:06:40.637
The immobility permits this
because a thin barrier is a weak barrier,

00:06:40.661 --> 00:06:45.469
and the weak barrier would rupture
if it was actively being ventilated

00:06:45.493 --> 00:06:47.308
like a mammalian lung.

NOTE Paragraph

00:06:48.056 --> 00:06:49.589
So why do we care about this?

00:06:49.613 --> 00:06:51.337
Why does this even matter?

00:06:52.083 --> 00:06:56.338
Oxygen more easily diffuses
across a thin membrane,

00:06:57.536 --> 00:07:03.627
and a thin membrane is one way
of enhancing respiration

00:07:03.651 --> 00:07:05.987
under low-oxygen conditions --

00:07:06.011 --> 00:07:10.592
low-oxygen conditions
like that of the Triassic period.

00:07:11.425 --> 00:07:16.130
So, if dinosaurs did indeed
have this type of lung,

00:07:16.154 --> 00:07:20.211
they'd be better equipped to breathe
than all other animals,

00:07:20.235 --> 00:07:22.369
including mammals.

NOTE Paragraph

00:07:22.851 --> 00:07:26.466
So do you remember the extant
phylogenetic bracket method

00:07:26.490 --> 00:07:29.369
where we take the anatomy
of modern animals,

00:07:29.393 --> 00:07:31.928
and we apply that to the fossil record?

00:07:31.952 --> 00:07:36.814
So, clue number one
was the forked ribs of modern birds.

00:07:36.838 --> 00:07:41.249
Well, we find that in pretty much
the majority of dinosaurs.

00:07:41.734 --> 00:07:46.531
So that means that the top surface
of the lungs of dinosaurs

00:07:46.555 --> 00:07:48.869
would be locked into place,

00:07:48.893 --> 00:07:51.845
just like modern birds.

NOTE Paragraph

00:07:51.869 --> 00:07:55.406
Clue number two is vertebral pneumaticity.

00:07:55.430 --> 00:08:00.237
We find this in sauropod dinosaurs
and theropod dinosaurs,

00:08:00.261 --> 00:08:03.536
which is the group that contains
predatory dinosaurs

00:08:03.560 --> 00:08:05.782
and gave rise to modern birds.

00:08:06.250 --> 00:08:11.589
And while we don't find evidence
of fossilized lung tissue in dinosaurs,

00:08:11.613 --> 00:08:16.162
vertebral pneumaticity gives us evidence
of what the lung was doing

00:08:16.186 --> 00:08:18.638
during the life of these animals.

00:08:19.211 --> 00:08:24.556
Lung tissue or air sac tissue
was invading the vertebrae,

00:08:24.580 --> 00:08:27.087
hollowing them out
just like a modern bird,

00:08:27.111 --> 00:08:31.245
and locking regions
of the respiratory system into place,

00:08:31.269 --> 00:08:32.869
immobilizing them.

00:08:34.138 --> 00:08:35.923
The forked ribs

00:08:35.947 --> 00:08:38.791
and the vertebral pneumaticity together

00:08:38.815 --> 00:08:43.722
were creating an immobilized,
rigid framework

00:08:43.746 --> 00:08:46.688
that locked the respiratory
system into place

00:08:46.712 --> 00:08:52.486
that permitted the evolution of that
superthin, superdelicate blood-gas barrier

00:08:52.510 --> 00:08:55.366
that we see today in modern birds.

NOTE Paragraph

00:08:55.390 --> 00:08:58.880
Evidence of this straightjacketed
lung in dinosaurs

00:08:58.904 --> 00:09:02.378
means that they had
the capability to evolve a lung

00:09:02.402 --> 00:09:04.140
that would have been able to breathe

00:09:04.164 --> 00:09:09.283
under the hypoxic, or low-oxygen,
atmosphere of the Triassic period.

00:09:09.981 --> 00:09:15.078
This rigid skeletal setup in dinosaurs
would have given them

00:09:15.102 --> 00:09:20.585
a significant adaptive advantage
over other animals, particularly mammals,

00:09:20.609 --> 00:09:23.310
whose flexible lung couldn't have adapted

00:09:23.334 --> 00:09:27.129
to the hypoxic, or low-oxygen,
atmosphere of the Triassic.

00:09:27.664 --> 00:09:32.734
This anatomy may have been
the secret weapon of dinosaurs

00:09:32.758 --> 00:09:35.702
that gave them that advantage
over other animals.

00:09:36.096 --> 00:09:38.900
And this gives us an excellent launchpad

00:09:38.924 --> 00:09:43.832
to start testing the hypotheses
of dinosaurian diversification.

NOTE Paragraph

00:09:43.856 --> 00:09:47.750
This is the story of
the dinosaurs' beginning,

00:09:47.774 --> 00:09:52.272
and it's just the beginning of the story
of our research into this subject.

NOTE Paragraph

00:09:52.932 --> 00:09:54.124
Thank you.

NOTE Paragraph

00:09:54.148 --> 00:09:57.109
(Applause)