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Documentary, PaeoWord S01E07 - Tale Of The Sail
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AnimalsTranscript
00:02Millions of years before the great dinosaurs, monsters of a different sort ruled the world.
00:08Strange sail back creatures like these for our ancient ancestors.
00:15Skeletons hidden in our closet.
00:19As paleontologists dig up new clues, modern technology sheds new light on the distant past.
00:27Meet a member of our family as we unearth a bizarre tale of the sailor.
01:06Seventy-five miles northwest of Fort Worth lie the Texas red beds.
01:11This shabby stretch of land in Archer City County, Texas, gets its name from the dusty red soil and the
01:18punishing heat.
01:20By noon, the hot July sun will bake the earth to a temperature of more than 110 degrees.
01:31Rattlesnakes, scorpions and other poisonous creatures make their home here.
01:36One touch from this centipede's legs can prove lethal.
01:41Deadly creatures roam this valley millions of years before the dinosaurs.
01:48For two decades, paleontologist Tim Rowe has been studying the creatures of this period.
01:54Today, Rowe and his team of paleontologists brave the elements, searching for clues that will bring them face to face
02:00with the fiercest creature ever to inhabit the red beds.
02:05Dimetrodon, a reptile known for the enormous sail on its back.
02:14When Dimetrodon ruled the Texas red beds, the land was fertile and wet.
02:21Today, Dimetrodon's remains litter the rocky, barren landscape.
02:25The soil here is so rich in fossils that each new rainstorm exposes new specimens.
02:31If you don't know what to look for, you might miss them.
02:34But Tim Rowe easily spots the backbone of a Dimetrodon lying in the dust.
02:39Yeah, it's another Dimetrodon vertebrae.
02:42Yeah, it sure looks like one.
02:44It's just going to be keeled down the ventral.
02:46Soon, this one small bone from a Dimetrodon's spine leads to an even bigger find.
02:51A skeleton that includes part of the animal's sail.
02:56That's a really beautiful specimen.
02:58It's wonderful to be able to come out here in just a few hours and see something like this.
03:02Something I've never seen before and not have to sweat for the entire summer, you know.
03:06Just dig into the ground in a couple hours and there it is.
03:09It's really wonderful.
03:11Bit by bit, these discoveries are writing a story that affects us all.
03:17More than just a simple reptile, not quite a dinosaur,
03:21this monster, Dimetrodon, is also our ancient forefather.
03:27The story of Dimetrodon and its descendants is also our story.
03:31It's our own family history and we can track it very deeply back into time.
03:37Most people think of human history in terms of a few millions of years and our relationships to apes,
03:42but we can track our own history from a form like this back nearly 300 million years
03:46to an animal like this, like Dimetrodon here.
03:50Armed with a powerful jaw and razor sharp teeth,
03:53this deadly predator grew up to 12 feet long, the size of a hippopotamus.
04:01With innovations such as the sail on its back, Dimetrodon and its close relatives represent a new kind of creature,
04:08more advanced than earlier reptiles, but not quite a mammal.
04:12These proto-mammals, as they are called, were the prototypes that set the stage for mammal and ultimately human development.
04:22This distant ancestor is the oldest portrait in our family album.
04:26He lived more than 280 million years ago, a time known as the Permian period.
04:32Animals competed violently for survival.
04:35Success required some sort of advantage.
04:40Dimetrodon's advantage was as plain as the sail on his back.
04:46The sail of Dimetrodon is a really interesting feature.
04:49It's made up of a series of tall spines like this that form a big sail extending behind the skull
04:55of the animal.
04:55There's no animal alive that has a feature of anything like this, and so its function is really controversial.
05:00There are basically two ideas on what the sail is for.
05:03The first, and probably most widely accepted, is that it's a heat radiator.
05:07It's for gaining or losing heat more quickly.
05:10The second one is for sex.
05:13Was Dimetrodon's enormous sail simply a way to impress a date?
05:19Nicholas Houghton doesn't think so.
05:21Here at the Smithsonian Institution in Washington, D.C., he studied mammal-like reptiles for decades.
05:27He thinks the sail was used to regulate body temperature.
05:33The sail probably functioned as both a radiator and a heat absorber.
05:38As a heat absorber, it would allow an animal to warm up faster than the animals were not so equipped.
05:46And if it was a predator, it would get going after lunch more quickly.
05:49If it were prey, it could get out of the way faster.
05:52So it probably got pretty hot, too.
05:54And this would be a problem with an animal as big as Dimetrodon.
05:57And to get rid of excess heat, it would simply turn so that the sail was parallel with the rays
06:05of the sun,
06:06and its higher temperature would then be radiated off into the air, and it could cool off.
06:11Others, such as maverick paleontologist Robert Baca, disagree.
06:16The people who want to make anything sticking out of the body a cooling mechanism should watch more animals in
06:21the zoo.
06:22Things that stick out of your head or stick out of your back are nearly always used, first, to intimidate
06:27rivals, sexual rivals.
06:29Second, maybe as a radiator.
06:31But the main reason for moose antlers or finbacks is to intimidate your rivals.
06:38Though opinions about Dimetrodon's sail may differ,
06:42most scientists agree that Dimetrodon and its relatives mark a key step
06:47between the cold-bloodedness of reptiles and the warm-bloodedness of mammals.
06:53Reptiles rely on the sun to raise their metabolism.
06:57They're cold-blooded.
06:58Without the sun's warming rays, they become slow, still, and helpless.
07:03But mammals, like us, have more sophisticated internal machinery.
07:07We can generate the energy our bodies require, no matter what time of the day it is.
07:13We're warm-blooded.
07:15Warm-bloodedness is like keeping your house warm by opening all the windows and turning the thermostat way up.
07:22Constantly producing a lot of heat, most of which flies out the window, but you keep your house warm.
07:27The reason it's an advantage is you're ready for any sort of situation.
07:31If it suddenly gets cold, suddenly starts raining, suddenly gets dark or cloudy,
07:37you've got so much body heat, you can keep your body temperature high.
07:40So warm-bloodedness is the best way to be ready for any challenge.
07:46Dimetrodon used its sail to warm itself earlier in the morning.
07:49Other reptiles its size might take two hours to warm up.
07:53Dimetrodon could get moving in half that time.
07:55While potential reptilian prey waited for their blood to warm, Dimetrodon hunted.
08:01Then, as now, the early bird got the worm.
08:04Its victims included other proto-mammals such as Ophiakodon.
08:08It was perhaps the largest land animal of the Carboniferous period 300 million years ago.
08:15It grew up to 15 feet long and crawled along the ground on stunted legs.
08:21Ophiakodon means snake teeth.
08:23It was named for its teeth which curve backwards as a snake's.
08:27But neither its size nor its sharp teeth could protect it against the powerful jaws of the more advanced Dimetrodon.
08:36The lizard-like Ophiakodon and its kin gave rise to two lines of sailback reptiles.
08:42One included the small plant-eating Adaphosaurus, an evolutionary dead end.
08:48From the other line sprang Dimetrodon.
08:51Its success at temperature regulation provided the mammal-like reptiles with an early and powerful lead against the true reptiles.
08:59A battle for dominance of the planet was just beginning.
09:06The predator Dimetrodon, no ordinary reptile, but the first of a whole new line of proto-mammals.
09:13Reptiles have one kind of teeth uniformly throughout their mouth, but not Dimetrodon.
09:19Its name means two types of teeth, and that's exactly what we find in its mouth.
09:26An interesting point of resemblance between us and Dimetrodon is the dentition, the teeth.
09:32Dimetrodon has simple incisors followed by a specialized canine and a series of teeth of different sizes that are specialized
09:39behind the canine.
09:40This feature is not something that we find very commonly distributed throughout the animal kingdom.
09:45In fact, it's really only found in one other group, in mammals.
09:53Mammals, like Dimetrodon, have a dentition that's made up of simple, specialized incisors, a canine.
09:58Of course, our canine's pretty small, but it's still a canine.
10:01And behind the canine are a series of specialized, differentiated teeth of different sizes that perform different functions than the
10:07teeth in the front of the jaw.
10:09This feature links us with Dimetrodon, like it or not.
10:13You could pick your friends, but you can't pick your relatives.
10:16With the development of specialized teeth, Dimetrodon was one step closer toward becoming a mammal.
10:24360 million years ago, before Dimetrodon, the first creatures crawled out of the ocean and invaded the lush, marshy land
10:32at the edges of the continents.
10:33These simple, four-legged creatures, early amphibians, began spreading over the earth.
10:40Within 20 million years, they diversified, giving rise to the earliest reptiles.
10:47But the early reptiles soon reached a momentous fork in the evolutionary river.
10:52They split into two groups, and these two different designs began to compete for supremacy.
10:58From generation to generation, over millions of years, each line improved and perfected its design.
11:05The only difference between them was a simple hole in the head.
11:10But this seemingly trivial detail made all the difference in the world.
11:16Most of the early reptiles developed into a line known as the Diapsids, which means they had two openings in
11:23the back of their skulls.
11:24Over the course of millions of years, the Diapsids evolved into dinosaurs, lizards, crocodiles, and all modern reptiles.
11:33This is a crocodilian, and this is a Diapsid.
11:37Here's the hole where the eyeball would set, and behind it, on either side, are two openings through which the
11:42jaw muscles can expand, without squeezing the brain.
11:45This animal closes its jaws, the muscles can expand upwards and outwards here, instead of squeezing the brain.
11:50This ultimately enabled this lineage to evolve a larger brain and a more powerful bite, a smarter, better predator.
11:58But Dimetrodon's line chose to follow a different path.
12:01For reasons that aren't entirely clear, these early reptiles developed only a single hole in the back of their skulls.
12:08We call this group Synapsids.
12:10All proto-mammals were Synapsids, including Dimetrodon.
12:15From this line, cows, dogs, humans, and all other mammals evolved.
12:21This is one of our extinct relatives, and it's a Synapsid.
12:25Here's the hole where the eyeball would set, and this opening back here is the Synapsid opening.
12:31This is for the jaw muscles to expand outwards.
12:34If you turn the skull over, it's a little more clear what I mean by that.
12:38Here and here are where the right and left jaw muscles set, and squeezed between them is the brain.
12:43When this animal closes its lower jaws, it would squeeze the brain if there weren't some room on the side
12:49of its head for the jaw muscles to expand outwards.
12:52Being a Synapsid has to do with developing a stronger bite to permit larger jaw muscles to evolve, and at
12:59the same time to permit a larger brain to evolve.
13:02This is a human skull, and this skull shows to which group we belong.
13:07Here's the opening where the eyeball would sit, and behind it is a single opening.
13:12This is a Synapsid.
13:16The Synapsid condition allows for the jaw muscles to expand sideways here without squeezing the brain between them.
13:23This permits us to have a much larger brain without compromising the effectiveness of our bite.
13:29One extra little hole in the skull made such a big difference in the development of the proto-mammals.
13:38Over millions of years, this innovation led these creatures to develop mechanisms for more sophisticated hearing and sharper senses.
13:47This new skull design spurred the evolution of the three-boned inner ear, superior to the reptile's single ear bone.
13:57So, for example, in this jaw of Dimitrodon, there's a little flange of bone here that was involved in sound
14:04reception.
14:04And this flange of bone represents a significant step towards the origin of mammals.
14:09This three-boned design remains in mammals today.
14:13Better hearing and a better sense of smell made these creatures better hunters.
14:17The world quickly became a scarier place.
14:25To attack or run requires speed and endurance.
14:29And the proto-mammals adapted to survive.
14:31The arms race of the predators became more of a leg race.
14:36From the ancestors of Ophiocodon, 340 million years ago, to Dimitrodon, 280 million years ago,
14:44we see the legs begin to shift from the sides further under their bodies.
14:49By the time the saber-toothed Inostransivia alexandrii terrorized the swamp forests of ancient Russia 245 million years ago,
14:58proto-mammals had clearly made the transition from reptilian to mammal-like posture.
15:04Their metabolism, too, may have become truly warm-blooded.
15:13With a faster gait, the mammal-like reptiles took possession of the land masses.
15:18No simple reptile could stand up to these formidable predators.
15:22For 50 million years, they dominated and terrorized the planet.
15:28At the same time, evolution took a branch of proto-mammals on a wild detour,
15:33producing aggressive animals known as head-butters.
15:37Many species evolved strange horn-like growths and thick skulls.
15:41Some, like Estemina sucus, resembled the modern moose.
15:45Others, with knobs and bumps covering their faces, could only be compared to monsters of the imagination.
15:54These thick and strange skulls developed because butting heads became part of their mating rituals.
16:00It was a strange way of showing their mates just how hot-blooded they had become.
16:06Long before the hot-blooded head-butters, Dimitrodon may have used his sail as a sexual lure or a signal
16:14to rivals,
16:14perhaps by changing its color.
16:17Dimitrodon was a cold-blooded critter, got to understand.
16:20Its immediate descendants were the first hot-bloods.
16:23They included the first head-butters, animals with huge bony crests around their eyes,
16:28for whacking and thwacking each other.
16:30Now think about that.
16:31When hot-bloodedness evolved, suddenly you have a lot of energy.
16:34You, the individual critter, what are you going to use that energy for?
16:37Well, you can keep yourself warm and you can migrate, but in the breeding season,
16:42you can use that energy for whacking and thwacking and pushing and shoving
16:46and ramming your sexual rival right in the guts.
16:50So it actually makes a lot of sense that physical combat and courtship would evolve
16:54right after warm-bloodedness, first of all.
16:58The walrus-like Lystrosaurus typifies one of the later head-butters.
17:03The skull is thick and nearly flat.
17:05Millions of years of head-butting behavior produced this strange creature
17:10with a turtle-like beak squashed against a flattened face.
17:16Mammal-like reptiles grew and flourished.
17:18They had taken important steps from reptilian to mammalian form.
17:23They had struggled up the evolutionary ladder, but then suddenly and inexplicably,
17:27the dinosaurs took control.
17:32The proto-mammals began to disappear.
17:36Despite the great evolutionary strides made by the proto-mammals, something went terribly wrong.
17:44At the beginning of the Triassic period, 245 million years ago, the highly developed
17:50and greatly diversified proto-mammals began to die off in record numbers.
17:55The larger they were, the more vulnerable.
17:57And at the same time, the first little dinosaurs were mysteriously thriving.
18:04The dinosaurs began a long conquest of the planet.
18:09In battle after battle, they pushed the proto-mammals to the brink of extinction.
18:18The proto-mammals' dynamic and seemingly unstoppable rise from lizard-like Ophiacodon to sail-back Dimetrodon
18:27to the truly warm-blooded and dog-like Cynognathus suddenly faltered.
18:33To survive, the late proto-mammals, like Thrynaxodon, were forced to downsize.
18:38They held on to life in forms no larger than a rodent.
18:43Reduced in size and pitched against the skillful dinosaur predators,
18:47proto-mammals had to adapt to nighttime activity to survive.
18:52Now technology is revealing what these small creatures were doing in the darkness.
18:58They were getting smarter.
19:00With lasers, x-rays, and CAT scan images, Tim Rowe and his team can actually get inside the head of
19:06a proto-mammal.
19:16They're discovering the story of how mammalian intelligence developed.
19:31The CAT scanner uses an x-ray beam to effectively slice this specimen as if it were a loaf of
19:37bread,
19:37simply slicing it from bottom to top in this orientation.
19:41And what you're looking at is a single slice that's about the thickness of a piece of paper that was
19:46taken through this skull.
19:49Here's the next slice, a little higher.
19:51Here's the next slice, a little higher yet.
19:53A little higher, a little higher.
19:56This slice shows the matrix here in dark.
19:59It shows the bone and teeth in light.
20:02And by going through this slice, by slice, by slice, we can see all kinds of details of the anatomy
20:09of thrynaxidon.
20:11And with a computer, we can not only slice through this frame at a time, but we can animate it.
20:18And here you can see a passage from the bottom all the way through the very top of the skull.
20:23There's the very top right there.
20:29And that's it.
20:30Go all the way through this specimen automatically like that.
20:33Visualize the internal details, the external details in just a few seconds.
20:37With its small head and pointy snout, this mean-looking animal was one of the most advanced of the proto
20:44-mammals.
20:45Small, but deadly.
20:46It had a vicious set of teeth that could shear and slice its prey.
20:50It stole through the forests, bullying and killing animals its size or smaller.
20:56As proto-mammals went, the size of its brain made it a genius.
21:00But compared to the brain of an opossum, it was a mental midget.
21:06Yet even with these new technologies, many mysteries about the development of mammals remain unanswered by the fossil record.
21:13We do not know when many significant mammal traits developed, such as mothers giving live birth instead of the reptile
21:20trait of laying eggs.
21:21Or when these mothers developed mammary glands to suckle their young.
21:27Many of these mysteries could be answered if we had samples of soft tissue from the extinct animals.
21:33Unfortunately, fossilization preserves only the bones and teeth, rarely the soft tissue that surrounds them.
21:41Whether or not proto-mammals had developed fur by the time of the Thrinaxodon is a hair-raising question that
21:47has spurred serious debate.
21:49Nicholas Houghton thinks they had.
21:52There's great big holes in the front of its muzzle, like this.
21:57These holes were passages for blood vessels and nerves, which may have been the innervation and blood supply of whiskers,
22:06which are sensory organs.
22:08But whiskers are specialized hair, and if they had whiskers, maybe they had hair also.
22:13So, a living Thrinaxodon may have looked even more like a possum than their skulls do.
22:19In other words, they were warm-blooded and hairy.
22:22But the latest CAT scan images lead Tim Rowe to think that Thrinaxodon had little or no hair.
22:28This area of the brain is involved in mapping the sensory input from the hair over our body.
22:33In Thrinaxodon, that region is missing.
22:36So, if Thrinaxodon did have hair, it didn't have as much hair as modern mammals did.
22:40Hair didn't provide quite the sensory input.
22:42If it didn't have as much hair, it also wouldn't provide quite the insulation that it provides in modern mammals.
22:47So, if Thrinaxodon did have hair, it wasn't keeping it as warm as the hair keeps modern mammals.
22:53Thrinaxodon probably wasn't warm-blooded quite in the sense that modern mammals are.
22:58In the beginning of the Jurassic Age, 210 million years ago, we see the first full mammals, creatures like the
23:06Morganucodon.
23:07It was as small as a squirrel.
23:09For 145 million years, mammals grew no larger.
23:15Until 65 million years ago, when in a twist of evolutionary fate, the Great Extinction killed off all dinosaurs.
23:29With the dinosaurs out of the way, mammals rapidly evolved and some grew in size.
23:36The millions of years they had hidden themselves had paid off.
23:40They now assumed domination of the planet.
23:43The enormous diversity of modern mammals owes its evolutionary heritage to Dimetrodon and the other fantastic proto-mammals from virtually
23:53the beginning of life on land.
23:55From this incredible tale of the sail came the traits that make us mammals and make us humans.
24:32The Viewer's
25:02Transcription by CastingWords
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