[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.02,0:00:03.44,Default,,0000,0000,0000,,We've all heard about\Nhow the dinosaurs died.
Dialogue: 0,0:00:04.28,0:00:06.24,Default,,0000,0000,0000,,The story I'm going to tell you
Dialogue: 0,0:00:06.26,0:00:10.87,Default,,0000,0000,0000,,happened over 200 million years\Nbefore the dinosaurs went extinct.
Dialogue: 0,0:00:11.48,0:00:14.37,Default,,0000,0000,0000,,This story starts at the very beginning,
Dialogue: 0,0:00:14.39,0:00:16.74,Default,,0000,0000,0000,,when dinosaurs were just\Ngetting their start.
Dialogue: 0,0:00:17.27,0:00:19.99,Default,,0000,0000,0000,,One of the biggest mysteries\Nin evolutionary biology
Dialogue: 0,0:00:20.02,0:00:23.03,Default,,0000,0000,0000,,is why dinosaurs were so successful.
Dialogue: 0,0:00:23.55,0:00:27.31,Default,,0000,0000,0000,,What led to their global dominance\Nfor so many years?
Dialogue: 0,0:00:27.90,0:00:31.41,Default,,0000,0000,0000,,When people think about\Nwhy dinosaurs were so amazing,
Dialogue: 0,0:00:31.44,0:00:35.24,Default,,0000,0000,0000,,they usually think about the biggest\Nor the smallest dinosaur,
Dialogue: 0,0:00:35.27,0:00:36.71,Default,,0000,0000,0000,,or who was the fastest,
Dialogue: 0,0:00:36.74,0:00:38.30,Default,,0000,0000,0000,,or who had the most feathers,
Dialogue: 0,0:00:38.33,0:00:41.23,Default,,0000,0000,0000,,the most ridiculous armor,\Nspikes or teeth.
Dialogue: 0,0:00:42.13,0:00:46.11,Default,,0000,0000,0000,,But perhaps the answer had to do\Nwith their internal anatomy --
Dialogue: 0,0:00:46.13,0:00:48.33,Default,,0000,0000,0000,,a secret weapon, so to speak.
Dialogue: 0,0:00:48.72,0:00:52.42,Default,,0000,0000,0000,,My colleagues and I,\Nwe think it was their lungs.
Dialogue: 0,0:00:53.15,0:00:57.40,Default,,0000,0000,0000,,I am both a paleontologist\Nand a comparative anatomist,
Dialogue: 0,0:00:57.43,0:00:59.37,Default,,0000,0000,0000,,and I am interested in understanding
Dialogue: 0,0:00:59.40,0:01:02.80,Default,,0000,0000,0000,,how the specialized dinosaur lung\Nhelped them take over the planet.
Dialogue: 0,0:01:03.80,0:01:07.50,Default,,0000,0000,0000,,So we are going to jump back\Nover 200 million years
Dialogue: 0,0:01:07.52,0:01:09.28,Default,,0000,0000,0000,,to the Triassic period.
Dialogue: 0,0:01:09.30,0:01:11.69,Default,,0000,0000,0000,,The environment was extremely harsh,
Dialogue: 0,0:01:11.72,0:01:13.36,Default,,0000,0000,0000,,there were no flowering plants,
Dialogue: 0,0:01:13.38,0:01:15.63,Default,,0000,0000,0000,,so this means that there was no grass.
Dialogue: 0,0:01:15.66,0:01:20.06,Default,,0000,0000,0000,,So imagine a landscape\Nfilled with all pine trees and ferns.
Dialogue: 0,0:01:20.59,0:01:24.04,Default,,0000,0000,0000,,At the same time,\Nthere were small lizards,
Dialogue: 0,0:01:24.06,0:01:26.46,Default,,0000,0000,0000,,mammals, insects,
Dialogue: 0,0:01:26.48,0:01:30.79,Default,,0000,0000,0000,,and there were also carnivorous\Nand herbivorous reptiles --
Dialogue: 0,0:01:30.82,0:01:33.10,Default,,0000,0000,0000,,all competing for the same resources.
Dialogue: 0,0:01:33.45,0:01:34.100,Default,,0000,0000,0000,,Critical to this story
Dialogue: 0,0:01:35.02,0:01:40.35,Default,,0000,0000,0000,,is that oxygen levels have been estimated\Nto have been as low as 15 percent,
Dialogue: 0,0:01:40.37,0:01:42.52,Default,,0000,0000,0000,,compared to today's 21 percent.
Dialogue: 0,0:01:42.93,0:01:46.52,Default,,0000,0000,0000,,So it would have been crucial\Nfor dinosaurs to be able to breathe
Dialogue: 0,0:01:46.54,0:01:48.42,Default,,0000,0000,0000,,in this low-oxygen environment,
Dialogue: 0,0:01:48.44,0:01:50.30,Default,,0000,0000,0000,,not only to survive
Dialogue: 0,0:01:50.32,0:01:53.01,Default,,0000,0000,0000,,but to thrive and to diversify.
Dialogue: 0,0:01:54.46,0:01:57.56,Default,,0000,0000,0000,,So, how do we know\Nwhat dinosaur lungs were even like,
Dialogue: 0,0:01:57.58,0:02:02.72,Default,,0000,0000,0000,,since all that remains of a dinosaur\Ngenerally is its fossilized skeleton?
Dialogue: 0,0:02:03.26,0:02:08.35,Default,,0000,0000,0000,,The method that we use is called\N"extant phylogenetic bracketing."
Dialogue: 0,0:02:09.08,0:02:13.13,Default,,0000,0000,0000,,This is a fancy way of saying\Nthat we study the anatomy --
Dialogue: 0,0:02:13.15,0:02:16.73,Default,,0000,0000,0000,,specifically in this case,\Nthe lungs and skeleton --
Dialogue: 0,0:02:16.75,0:02:20.73,Default,,0000,0000,0000,,of the living descendants of dinosaurs\Non the evolutionary tree.
Dialogue: 0,0:02:21.24,0:02:24.20,Default,,0000,0000,0000,,So we would look at the anatomy of birds,
Dialogue: 0,0:02:24.22,0:02:27.08,Default,,0000,0000,0000,,who are the direct\Ndescendants of dinosaurs,
Dialogue: 0,0:02:27.10,0:02:29.45,Default,,0000,0000,0000,,and we'd look at\Nthe anatomy of crocodilians,
Dialogue: 0,0:02:29.48,0:02:31.43,Default,,0000,0000,0000,,who are their closest living relatives,
Dialogue: 0,0:02:31.45,0:02:34.44,Default,,0000,0000,0000,,and then we would look at\Nthe anatomy of lizards and turtles,
Dialogue: 0,0:02:34.47,0:02:37.07,Default,,0000,0000,0000,,who we can think of like their cousins.
Dialogue: 0,0:02:37.10,0:02:40.53,Default,,0000,0000,0000,,And then we apply these anatomical data\Nto the fossil record,
Dialogue: 0,0:02:40.56,0:02:44.20,Default,,0000,0000,0000,,and then we can use that\Nto reconstruct the lungs of dinosaurs.
Dialogue: 0,0:02:44.22,0:02:46.27,Default,,0000,0000,0000,,And in this specific instance,
Dialogue: 0,0:02:46.29,0:02:51.20,Default,,0000,0000,0000,,the skeleton of dinosaurs most closely\Nresembles that of modern birds.
Dialogue: 0,0:02:51.70,0:02:56.46,Default,,0000,0000,0000,,So, because dinosaurs were competing with\Nearly mammals during this time period,
Dialogue: 0,0:02:56.49,0:03:00.14,Default,,0000,0000,0000,,it's important to understand\Nthe basic blueprint of the mammalian lung.
Dialogue: 0,0:03:00.60,0:03:03.43,Default,,0000,0000,0000,,Also, to reintroduce you\Nto lungs in general,
Dialogue: 0,0:03:03.46,0:03:06.09,Default,,0000,0000,0000,,we will use my dog Mila of Troy,
Dialogue: 0,0:03:06.11,0:03:08.15,Default,,0000,0000,0000,,the face that launched a thousand treats,
Dialogue: 0,0:03:08.18,0:03:09.40,Default,,0000,0000,0000,,as our model.
Dialogue: 0,0:03:09.42,0:03:11.00,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:03:11.03,0:03:14.76,Default,,0000,0000,0000,,This story takes place\Ninside of a chest cavity.
Dialogue: 0,0:03:14.79,0:03:17.98,Default,,0000,0000,0000,,So I want you to visualize\Nthe ribcage of a dog.
Dialogue: 0,0:03:18.01,0:03:20.47,Default,,0000,0000,0000,,Think about how\Nthe spinal vertebral column
Dialogue: 0,0:03:20.49,0:03:23.76,Default,,0000,0000,0000,,is completely horizontal to the ground.
Dialogue: 0,0:03:23.78,0:03:26.36,Default,,0000,0000,0000,,This is how the spinal\Nvertebral column is going to be
Dialogue: 0,0:03:26.38,0:03:28.79,Default,,0000,0000,0000,,in all of the animals\Nthat we'll be talking about,
Dialogue: 0,0:03:28.81,0:03:30.31,Default,,0000,0000,0000,,whether they walked on two legs
Dialogue: 0,0:03:30.33,0:03:31.49,Default,,0000,0000,0000,,or four legs.
Dialogue: 0,0:03:31.51,0:03:36.02,Default,,0000,0000,0000,,Now I want you to climb inside\Nof the imaginary ribcage and look up.
Dialogue: 0,0:03:36.94,0:03:39.02,Default,,0000,0000,0000,,This is our thoracic ceiling.
Dialogue: 0,0:03:39.48,0:03:43.40,Default,,0000,0000,0000,,This is where the top surface of the lungs\Ncomes into direct contact
Dialogue: 0,0:03:43.42,0:03:45.75,Default,,0000,0000,0000,,with the ribs and vertebrae.
Dialogue: 0,0:03:46.37,0:03:49.86,Default,,0000,0000,0000,,This interface is where\Nour story takes place.
Dialogue: 0,0:03:50.40,0:03:53.43,Default,,0000,0000,0000,,Now I want you to visualize\Nthe lungs of a dog.
Dialogue: 0,0:03:53.46,0:03:56.64,Default,,0000,0000,0000,,On the outside, it's like\Na giant inflatable bag
Dialogue: 0,0:03:56.67,0:04:00.08,Default,,0000,0000,0000,,where all parts of the bag\Nexpand during inhalation
Dialogue: 0,0:04:00.10,0:04:02.58,Default,,0000,0000,0000,,and contract during exhalation.
Dialogue: 0,0:04:02.60,0:04:05.88,Default,,0000,0000,0000,,Inside of the bag, there's a series\Nof branching tubes,
Dialogue: 0,0:04:05.90,0:04:08.38,Default,,0000,0000,0000,,and these tubes are called\Nthe bronchial tree.
Dialogue: 0,0:04:08.90,0:04:15.01,Default,,0000,0000,0000,,These tubes deliver the inhaled oxygen\Nto, ultimately, the alveolus.
Dialogue: 0,0:04:15.04,0:04:20.08,Default,,0000,0000,0000,,They cross over a thin membrane\Ninto the bloodstream by diffusion.
Dialogue: 0,0:04:20.57,0:04:22.75,Default,,0000,0000,0000,,Now, this part is critical.
Dialogue: 0,0:04:23.44,0:04:26.92,Default,,0000,0000,0000,,The entire mammalian lung is mobile.
Dialogue: 0,0:04:26.95,0:04:31.97,Default,,0000,0000,0000,,That means it's moving\Nduring the entire respiratory process,
Dialogue: 0,0:04:31.99,0:04:34.58,Default,,0000,0000,0000,,so that thin membrane,\Nthe blood-gas barrier,
Dialogue: 0,0:04:34.60,0:04:37.64,Default,,0000,0000,0000,,cannot be too thin or it will break.
Dialogue: 0,0:04:37.66,0:04:41.20,Default,,0000,0000,0000,,Now, remember the blood-gas barrier,\Nbecause we will be returning to this.
Dialogue: 0,0:04:41.72,0:04:43.21,Default,,0000,0000,0000,,So, you're still with me?
Dialogue: 0,0:04:43.23,0:04:45.86,Default,,0000,0000,0000,,Because we're going to start birds\Nand it gets crazy,
Dialogue: 0,0:04:45.88,0:04:47.32,Default,,0000,0000,0000,,so hold on to your butts.
Dialogue: 0,0:04:47.35,0:04:48.95,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:04:49.65,0:04:52.90,Default,,0000,0000,0000,,The bird is completely different\Nfrom the mammal.
Dialogue: 0,0:04:53.50,0:04:55.89,Default,,0000,0000,0000,,And we are going to be\Nusing birds as our model
Dialogue: 0,0:04:55.91,0:04:58.34,Default,,0000,0000,0000,,to reconstruct the lungs of dinosaurs.
Dialogue: 0,0:04:58.37,0:04:59.93,Default,,0000,0000,0000,,So in the bird,
Dialogue: 0,0:04:59.96,0:05:04.17,Default,,0000,0000,0000,,air passes through the lung,\Nbut the lung does not expand or contract.
Dialogue: 0,0:05:04.71,0:05:06.65,Default,,0000,0000,0000,,The lung is immobilized,
Dialogue: 0,0:05:06.67,0:05:08.96,Default,,0000,0000,0000,,it has the texture of a dense sponge
Dialogue: 0,0:05:08.99,0:05:14.20,Default,,0000,0000,0000,,and it's inflexible and locked into place\Non the top and sides by the ribcage
Dialogue: 0,0:05:14.22,0:05:17.31,Default,,0000,0000,0000,,and on the bottom\Nby a horizontal membrane.
Dialogue: 0,0:05:18.30,0:05:21.39,Default,,0000,0000,0000,,It is then unidirectionally ventilated
Dialogue: 0,0:05:21.41,0:05:25.40,Default,,0000,0000,0000,,by a series of flexible,\Nbag-like structures
Dialogue: 0,0:05:25.42,0:05:28.21,Default,,0000,0000,0000,,that branch off of the bronchial tree,
Dialogue: 0,0:05:28.23,0:05:29.82,Default,,0000,0000,0000,,beyond the lung itself,
Dialogue: 0,0:05:29.85,0:05:31.72,Default,,0000,0000,0000,,and these are called air sacs.
Dialogue: 0,0:05:32.25,0:05:37.61,Default,,0000,0000,0000,,Now, this entire extremely delicate setup\Nis locked into place
Dialogue: 0,0:05:37.63,0:05:40.82,Default,,0000,0000,0000,,by a series of forked ribs
Dialogue: 0,0:05:40.84,0:05:43.55,Default,,0000,0000,0000,,all along the thoracic ceiling.
Dialogue: 0,0:05:43.57,0:05:46.66,Default,,0000,0000,0000,,Also, in many species of birds,
Dialogue: 0,0:05:46.68,0:05:49.10,Default,,0000,0000,0000,,extensions arise from the lung
Dialogue: 0,0:05:49.13,0:05:50.67,Default,,0000,0000,0000,,and the air sacs,
Dialogue: 0,0:05:50.70,0:05:53.30,Default,,0000,0000,0000,,they invade the skeletal tissues --
Dialogue: 0,0:05:53.33,0:05:56.03,Default,,0000,0000,0000,,usually the vertebrae,\Nsometimes the ribs --
Dialogue: 0,0:05:56.06,0:05:59.01,Default,,0000,0000,0000,,and they lock the respiratory\Nsystem into place.
Dialogue: 0,0:05:59.04,0:06:02.47,Default,,0000,0000,0000,,And this is called\N"vertebral pneumaticity."
Dialogue: 0,0:06:02.50,0:06:05.74,Default,,0000,0000,0000,,The forked ribs and\Nthe vertebral pneumaticity
Dialogue: 0,0:06:05.76,0:06:09.28,Default,,0000,0000,0000,,are two clues that we can hunt for\Nin the fossil record,
Dialogue: 0,0:06:09.30,0:06:11.89,Default,,0000,0000,0000,,because these two skeletal traits
Dialogue: 0,0:06:11.92,0:06:16.64,Default,,0000,0000,0000,,would indicate that regions\Nof the respiratory system of dinosaurs
Dialogue: 0,0:06:16.66,0:06:18.34,Default,,0000,0000,0000,,are immobilized.
Dialogue: 0,0:06:21.20,0:06:23.81,Default,,0000,0000,0000,,This anchoring of the respiratory system
Dialogue: 0,0:06:23.83,0:06:27.74,Default,,0000,0000,0000,,facilitated the evolution\Nof the thinning of the blood-gas barrier,
Dialogue: 0,0:06:27.76,0:06:33.86,Default,,0000,0000,0000,,that thin membrane over which oxygen\Nwas diffusing into the bloodstream.
Dialogue: 0,0:06:34.75,0:06:40.64,Default,,0000,0000,0000,,The immobility permits this\Nbecause a thin barrier is a weak barrier,
Dialogue: 0,0:06:40.66,0:06:45.47,Default,,0000,0000,0000,,and the weak barrier would rupture\Nif it was actively being ventilated
Dialogue: 0,0:06:45.49,0:06:47.31,Default,,0000,0000,0000,,like a mammalian lung.
Dialogue: 0,0:06:48.06,0:06:49.59,Default,,0000,0000,0000,,So why do we care about this?
Dialogue: 0,0:06:49.61,0:06:51.34,Default,,0000,0000,0000,,Why does this even matter?
Dialogue: 0,0:06:52.08,0:06:56.34,Default,,0000,0000,0000,,Oxygen more easily diffuses\Nacross a thin membrane,
Dialogue: 0,0:06:57.54,0:07:03.63,Default,,0000,0000,0000,,and a thin membrane is one way\Nof enhancing respiration
Dialogue: 0,0:07:03.65,0:07:05.99,Default,,0000,0000,0000,,under low-oxygen conditions --
Dialogue: 0,0:07:06.01,0:07:10.59,Default,,0000,0000,0000,,low-oxygen conditions\Nlike that of the Triassic period.
Dialogue: 0,0:07:11.42,0:07:16.13,Default,,0000,0000,0000,,So, if dinosaurs did indeed\Nhave this type of lung,
Dialogue: 0,0:07:16.15,0:07:20.21,Default,,0000,0000,0000,,they'd be better equipped to breathe\Nthan all other animals,
Dialogue: 0,0:07:20.24,0:07:22.37,Default,,0000,0000,0000,,including mammals.
Dialogue: 0,0:07:22.85,0:07:26.47,Default,,0000,0000,0000,,So do you remember the extant\Nphylogenetic bracket method
Dialogue: 0,0:07:26.49,0:07:29.37,Default,,0000,0000,0000,,where we take the anatomy\Nof modern animals,
Dialogue: 0,0:07:29.39,0:07:31.93,Default,,0000,0000,0000,,and we apply that to the fossil record?
Dialogue: 0,0:07:31.95,0:07:36.81,Default,,0000,0000,0000,,So, clue number one\Nwas the forked ribs of modern birds.
Dialogue: 0,0:07:36.84,0:07:41.25,Default,,0000,0000,0000,,Well, we find that in pretty much\Nthe majority of dinosaurs.
Dialogue: 0,0:07:41.73,0:07:46.53,Default,,0000,0000,0000,,So that means that the top surface\Nof the lungs of dinosaurs
Dialogue: 0,0:07:46.56,0:07:48.87,Default,,0000,0000,0000,,would be locked into place,
Dialogue: 0,0:07:48.89,0:07:51.84,Default,,0000,0000,0000,,just like modern birds.
Dialogue: 0,0:07:51.87,0:07:55.41,Default,,0000,0000,0000,,Clue number two is vertebral pneumaticity.
Dialogue: 0,0:07:55.43,0:08:00.24,Default,,0000,0000,0000,,We find this in sauropod dinosaurs\Nand theropod dinosaurs,
Dialogue: 0,0:08:00.26,0:08:03.54,Default,,0000,0000,0000,,which is the group that contains\Npredatory dinosaurs
Dialogue: 0,0:08:03.56,0:08:05.78,Default,,0000,0000,0000,,and gave rise to modern birds.
Dialogue: 0,0:08:06.25,0:08:11.59,Default,,0000,0000,0000,,And while we don't find evidence\Nof fossilized lung tissue in dinosaurs,
Dialogue: 0,0:08:11.61,0:08:16.16,Default,,0000,0000,0000,,vertebral pneumaticity gives us evidence\Nof what the lung was doing
Dialogue: 0,0:08:16.19,0:08:18.64,Default,,0000,0000,0000,,during the life of these animals.
Dialogue: 0,0:08:19.21,0:08:24.56,Default,,0000,0000,0000,,Lung tissue or air sac tissue\Nwas invading the vertebrae,
Dialogue: 0,0:08:24.58,0:08:27.09,Default,,0000,0000,0000,,hollowing them out\Njust like a modern bird,
Dialogue: 0,0:08:27.11,0:08:31.24,Default,,0000,0000,0000,,and locking regions\Nof the respiratory system into place,
Dialogue: 0,0:08:31.27,0:08:32.87,Default,,0000,0000,0000,,immobilizing them.
Dialogue: 0,0:08:34.14,0:08:35.92,Default,,0000,0000,0000,,The forked ribs
Dialogue: 0,0:08:35.95,0:08:38.79,Default,,0000,0000,0000,,and the vertebral pneumaticity together
Dialogue: 0,0:08:38.82,0:08:43.72,Default,,0000,0000,0000,,were creating an immobilized,\Nrigid framework
Dialogue: 0,0:08:43.75,0:08:46.69,Default,,0000,0000,0000,,that locked the respiratory\Nsystem into place
Dialogue: 0,0:08:46.71,0:08:52.49,Default,,0000,0000,0000,,that permitted the evolution of that\Nsuperthin, superdelicate blood-gas barrier
Dialogue: 0,0:08:52.51,0:08:55.37,Default,,0000,0000,0000,,that we see today in modern birds.
Dialogue: 0,0:08:55.39,0:08:58.88,Default,,0000,0000,0000,,Evidence of this straightjacketed\Nlung in dinosaurs
Dialogue: 0,0:08:58.90,0:09:02.38,Default,,0000,0000,0000,,means that they had\Nthe capability to evolve a lung
Dialogue: 0,0:09:02.40,0:09:04.14,Default,,0000,0000,0000,,that would have been able to breathe
Dialogue: 0,0:09:04.16,0:09:09.28,Default,,0000,0000,0000,,under the hypoxic, or low-oxygen,\Natmosphere of the Triassic period.
Dialogue: 0,0:09:09.98,0:09:15.08,Default,,0000,0000,0000,,This rigid skeletal setup in dinosaurs\Nwould have given them
Dialogue: 0,0:09:15.10,0:09:20.58,Default,,0000,0000,0000,,a significant adaptive advantage\Nover other animals, particularly mammals,
Dialogue: 0,0:09:20.61,0:09:23.31,Default,,0000,0000,0000,,whose flexible lung couldn't have adapted
Dialogue: 0,0:09:23.33,0:09:27.13,Default,,0000,0000,0000,,to the hypoxic, or low-oxygen,\Natmosphere of the Triassic.
Dialogue: 0,0:09:27.66,0:09:32.73,Default,,0000,0000,0000,,This anatomy may have been\Nthe secret weapon of dinosaurs
Dialogue: 0,0:09:32.76,0:09:35.70,Default,,0000,0000,0000,,that gave them that advantage\Nover other animals.
Dialogue: 0,0:09:36.10,0:09:38.90,Default,,0000,0000,0000,,And this gives us an excellent launchpad
Dialogue: 0,0:09:38.92,0:09:43.83,Default,,0000,0000,0000,,to start testing the hypotheses\Nof dinosaurian diversification.
Dialogue: 0,0:09:43.86,0:09:47.75,Default,,0000,0000,0000,,This is the story of\Nthe dinosaurs' beginning,
Dialogue: 0,0:09:47.77,0:09:52.27,Default,,0000,0000,0000,,and it's just the beginning of the story\Nof our research into this subject.
Dialogue: 0,0:09:52.93,0:09:54.12,Default,,0000,0000,0000,,Thank you.
Dialogue: 0,0:09:54.15,0:09:57.11,Default,,0000,0000,0000,,(Applause)