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Documentary, PaleoWorld PaeoWord S01E04 - Back To The Seas
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AnimalsTranscript
00:03Fifty million years ago, a hungry wolf-like creature found the sea more inviting than the land.
00:09As schools of fish swam by, it put its paw in the water for the first time and snatched a
00:16meal.
00:17In that fleeting moment began one of the oddest tales in the history of life.
00:21The odyssey of a mammal and its journey back to the sea.
00:33Unfortunately, we will be one of the première names of the animals.
00:36The basic climatic sea animals, most of which are Và água, the other parts of the sea are prepared one
00:42of the fire in which we put with sea and theary.
00:49We will bless the sea and Norway also after in aid.
00:49Then, the sea.
00:49The sea ande.
00:59As strong as the prawn sea is in the grass.
01:08To confront a whale is to come face to face with a paradox.
01:12These exquisite creatures are remarkably well adapted to life in the sea, yet their ancestors
01:17were born on the land.
01:20Until recently no one knew where they came from.
01:23Their fossil tracks seemed to dissolve into the briny depths.
01:29What intrepid mammal, millions of years ago, seemingly reversed the course of evolution
01:35and set its sights on being a whale.
01:42Now a stunning cascade of whale fossils is emerging from the ancient seabeds, each an
01:48exquisite link in a once broken chain.
01:55Shark Tooth Hill, 75 miles inland from the Pacific Ocean in central California, is one
02:01of the most famous places in the world for finding fossils of sharks and ancient marine
02:05mammals.
02:11Here paleontologist Larry Barnes and his team have uncovered the remains of dozens of extinct
02:15sea creatures that lived 10 to 15 million years ago.
02:19The place that we're sitting now was at one time the bottom of the ocean and as evidence
02:24of that fact is here is this whale skull sitting at my feet.
02:27This is a wonderfully preserved skull.
02:29We can see here the brain case, this opening is where the nerve cord goes to the brain, the
02:34eye was under here, the nostrils here.
02:38Is there any other, I mean do you want to put Glyptol on a place else, we've got it.
02:41No, no I really don't want any more Glyptol on than we have to put on it.
02:45Why?
02:46Well, just…
02:48For more than a century, the origin of whales has sparked one of the most heated debates
02:53in evolutionary theory.
02:54It began with the publication of Charles Darwin's The Origin of Species of 1859.
03:01Darwin believed that animals changed over time because nature selected those individuals
03:06with the most advantageous characteristics, survival of the fittest.
03:12But how could earthbound creatures sprout wings and land mammals transform their legs into
03:17flippers?
03:21Darwin concocted a hypothetical tale to describe how one animal might evolve into a totally different
03:27species.
03:27He had heard of bears swimming for hours, with their mouths wide open catching insects.
03:33As I can see no difficulty, he wrote, in a race of bears being rendered by natural selection
03:37more aquatic in their structure and habits with larger and larger mouths, until a creature
03:43was produced as monstrous as a whale.
03:47For Darwin it was a political mistake, and he realized it immediately.
03:51Critics pounced on the tale.
03:53Darwin wrote a friend that it is laughable how often I have been attacked and
03:57misrepresented about this bear.
04:00The indication was not long in coming for some of Darwin's speculations.
04:05The year 1861 saw the discovery of a creature called Archaeaptrix, which was half bird, half
04:11reptile.
04:12What Darwin needed was an animal that was half bear, half whale, a link between the sea and
04:18the land.
04:21But there would be no discovery of a whale that could walk in Darwin's lifetime.
04:32Scientists did find early examples of whales over the next century, extinct whales unlike
04:37anything in the modern world.
04:39But they were all fully aquatic.
04:41There was no evidence of a link to land mammals.
04:47The search for a missing link would become a thorn in the side of paleontologists, according
04:52to Harvard biologist Stephen Jay Gould.
04:55Here you have whales, who are obviously mammals.
04:58They give birth to the young live.
05:00They have hair.
05:00They have all the features of mammals, but they look so unlike any standard mammal.
05:05Mammals are creatures with four legs that run around on land.
05:10And one yearns to have intermediary forms.
05:13But the fossil record is very imperfect and evolution is often very rapid.
05:19Today, paleontologists know that evolution usually proceeds in rapid spurts followed by
05:24long intervals without change.
05:28But in Darwin's day, evolution was perceived as slow and gradual.
05:33Scientists expected to quickly find the remains of a whale with legs if such a fossil existed.
05:39But they were in for a surprise.
05:41The discovery would wait more than 100 years.
05:50In Louisiana in 1834, paleontologist Richard Harland discovered the scattered remains of
05:55a huge animal.
05:57Harland mistakenly thought it was an enormous lizard, and so named it Bacillosaurus, King
06:03Lizard.
06:06Although the fossils were incomplete, Harland was confounded.
06:09Bacillosaurus was very old, yet looked like a modern whale.
06:14It was a fierce predator with flippers and a large fluke tail.
06:19With the oldest known Bacillosaurus, paleontologists had pushed the origin of whales back 40 million
06:25years.
06:26But there was still no hint of a missing link.
06:32Then, in 1989, in a remote desert in Egypt, Philip Gingrich of the University of Michigan
06:38discovered another Bacillosaurus fossil.
06:40This Bacillosaurus had legs.
06:44The legs were beautifully formed, but they were no bigger than a man's arm, too small to
06:50support an animal 50 feet long, weighing as much as 20 tons.
06:54So, what were they used for?
06:56I think they had to have some function, and it wasn't locomotion.
07:01I think they probably were used as copulatory guides, used to hang on during mating, which
07:08is, after all, very important in evolution.
07:14The revelation that Bacillosaurus had legs was tantalizing.
07:18It meant there had to be another, even older creature that could live and walk on land.
07:23Then, in a series of dramatic discoveries, the mystery was solved.
07:31The first big break came in 1983 in Pakistan.
07:35Fifty million years ago, this was the shore of an ancient sea called Tethys, that stretched
07:40all the way from Spain to Indonesia.
07:43But continental drift was rearranging the Earth's surface.
07:48India, then a separate land mass, was colliding with Asia, pushing up the Himalayas and emptying
07:54the Sea of Tethys.
07:57As India moved north, the sea became shallow, and that shallow sea became saline, and the
08:04high salinity and the exposure to sunlight made it highly productive.
08:09Now, plankton eat the nutrients in the water, fish eat the plankton, and the importance for whale
08:16evolution, I think, is that there was a big fish resource there waiting to be exploited.
08:23Scientists believe it was here that mammals first ventured back to the sea, and it was
08:28here that Philip Gingrich was looking for one creature and found another.
08:35What he found were the bones of an animal which, on closer examination, was clearly an early whale,
08:4110 million years older than Bacillosaurus.
08:43Gingrich named the new whale Pachycetus, whale from Pakistan.
08:51By reconstructing the skull of Pachycetus, Gingrich confirmed what many had long suspected,
08:57that whales evolved from a strange wolf-like animal with hooves, called a Masonicid.
09:05Here's a skull of a Masonicid and the skull of Pachycetus.
09:10If you compare them, you see that they're very similar to each other,
09:14and the main difference is that the front teeth in Pachycetus are smaller and much more pointed,
09:20which we interpret as being fish-eating teeth, whereas
09:24a Masonicids like this use their teeth more for bone-crushing and meat-tearing.
09:33Masonicids lived along the edges of the Sea of Tethys 50 million years ago.
09:39The teeming fish and other sea creatures in the waters of Tethys must have been a tempting sight.
09:44The main fish-eating predators, the giant marine reptiles such as Blesiosaurs and Mosasaurs,
09:50had gone extinct 10 million years earlier.
09:53For any land mammals willing to venture out from the shore,
09:57there was little competition from other animals for the abundant seafood that filled the waters of Tethys.
10:04If you have a shallow sea full of fish, the fish are going to die all the time,
10:08the fish wash up on the beaches, and a scavenger soon learns that there's a good meal on the beach.
10:14Pretty soon they're in the water catching the fish before they wash up,
10:18pretty soon they're chasing the weak and the dying fish,
10:21pretty soon they're chasing the living fish,
10:23and I think pretty soon you have a whale making its living by eating fish.
10:29Evolving from the Masonicids,
10:31Pacocetus had developed not only fish-eating teeth,
10:33but also a thickened earpad for hearing underwater.
10:37But Pacocetus was still very much a land mammal,
10:40spending only a small part of its time in the water.
10:43There remained a huge gap between this earliest whale and the fully aquatic Bacillosaurus
10:48that appeared 10 million years later.
10:51If Pacocetus had indeed been the prototype of a primitive whale and grown in size,
10:57lost its legs, and developed a whale's tail,
11:00more intermediate fossils would have to be found to prove it.
11:06Philip Gingrich was in luck when he returned to Pakistan in 1993.
11:10He discovered the remains of another whale which lived some 3 million years after Pacocetus.
11:16But the new whale, called Indocetus, was still more at home on land than in the sea.
11:22Unlike modern whales, it had tail bones that were fused together,
11:26giving it added strength to support its weight on land.
11:29Likewise, its well-developed hind legs showed that Indocetus was still primarily a land mammal.
11:38Once again, the missing link had eluded paleontologists.
11:42What they needed was an animal that could both walk and swim.
11:48On the ancient shores of Tethys, the fossil record would not disappoint them.
11:56The most finely forged link in the whale evolutionary chain emerged in 1994.
12:03Like his colleague Philip Gingrich, anatomist Hans Tewissen
12:06also made the long trek to Pakistan in search of ancient whales.
12:11In sediments almost 400 feet above the beds that yielded Pacocetus,
12:16Tewissen and his associates collected the remarkable skeleton of a new whale.
12:23In his lab at Northeastern Ohio University College of Medicine,
12:27Tewissen assembled the skeleton and realized he had found the evolutionary Holy Grail,
12:32a relatively complete fossil of the elusive, the impossible, the always derided missing link.
12:40He called it Ambulocetus natans, the walking, swimming whale.
12:47The most important single aspect of Ambulocetus is that it documents very well
12:51the shape and the size of the limbs, the forelimbs and the hindlimbs.
12:56This specimen is more complete than any other primitive whale,
13:01and it shows us, therefore, something about how these animals swam,
13:04how they use those limbs in the water and on land.
13:08Ambulocetus' complete limbs prove that it was the missing link.
13:12The enormous hind feet, held close to the body, were clearly adapted for swimming,
13:18yet were also capable of supporting the animal's weight on land.
13:23If you think, for instance, of recent seals or sea lions,
13:28those are animals that spend most of their time in the water,
13:30but they come back to land to do copulation, to give birth, to suck all their young.
13:36But pretty much everything else is done in the water, and probably whales went through a stage like that.
13:44Though Ambulocetus was a stunning discovery,
13:46showing a critical step in the evolution from Masonicid to Bacillosaurus,
13:50the remarkable parade of fossil evidence was not yet over.
13:55For Ambulocetus was an animal that swam with its feet, like seals.
13:59When did whales evolve into creatures that swam primarily with the use of their tails?
14:07Shortly after Tawesson's discovery of Ambulocetus early in 1994,
14:11Philip Gingrich found yet another whale, this one called Rhodocetus.
14:17In its tail, Gingrich found a key adaptation.
14:20Whereas the tail vertebra of early whales had been fused,
14:24enabling them to support themselves on land,
14:27the tail vertebra of Rhodocetus were detached from each other.
14:31It was a critical moment in whale evolution,
14:33because the tail of Rhodocetus could move freely up and down,
14:38propelling the animal through the water.
14:45From a prehistoric creature with hooves and the face of a wolf,
14:48to a graceful whale was a 10 million year odyssey from land to sea.
14:55As their mastery of the seas became complete,
14:58whales would continue the drama of evolution,
15:02diversifying into new and breathtaking creatures.
15:08For paleontologists, these were the discoveries of a lifetime.
15:12In the space of little more than a decade, from 1983 to 1994,
15:17the often stingy fossil record had revealed an embarrassment of riches.
15:23I would have expected that whales might have made the transition into the sea in 100,000 years.
15:30I would have expected it might have happened too fast to study.
15:34And believe me, I was happy when we found legs on a whale, Bacillosaurus,
15:4010 million years after Pachycetus,
15:42and we had 10 million years of geological history to work with,
15:46and lots of chances to find intermediates, because it didn't have to be that way.
15:55This then is the remarkable tale of the mammal's return to the sea.
16:01Some 300 million years after the first fish ventured out of the water
16:05to colonize the land, a mammal would begin to reverse the process.
16:1450 million years ago, the dinosaurs are long gone and mammals reign supreme.
16:20Among them are the strange Masonicids.
16:24The competition among mammals for food is fierce.
16:28Masonicids, ranging along the waterways in search of a meal,
16:31find the water more abundant than the land.
16:34Those that venture farther into the water survive.
16:37Those who don't, die out.
16:39Their only legacy will be in the sea.
16:46The Masonicids develop into Pachycetus, similar but with fish-eating teeth.
16:51Pachycetus is at home, both on land and at sea.
16:56Within a few million years, the seas have become the home of these creatures more than the land.
17:01But still they come ashore for the crucial part of their lives, mating and bearing their young.
17:07Pachycetus has become the walking, swimming whale, Ambulocetus natans.
17:13Another three million years and whales have evolved from Ambulocetus, dog-like tail and large head,
17:19to Rhodocetus, a long-dated skull, whale's tail and shrunken back legs.
17:24It can go ashore easily, but much prefers the sea, and may even bear its young there.
17:31Another few million years and whales have evolved from the seal-like Rhodocetus,
17:35into the sleek, elongated Bacillosaurus.
17:40They are utterly dedicated to life in the sea.
17:44Its tiny legs are useful for nothing more than hanging on during sex.
17:50It is a primitive whale and a fierce competitor.
17:55Bacillosaurus is still a long way from some of the gentle giants that struggle to survive in today's oceans.
18:02But finally, the land had been left behind.
18:06That such an evolutionary adventure could occur once is truly remarkable.
18:11That it occurred twice is astonishing, but clearly it did.
18:16About the same time that the strange Masonicid was testing the waters of Tethys and finding them to its liking,
18:22another ancient creature took the plunge.
18:27This one larger, slower and distinctly elephantine.
18:31Its gentle descendants would give rise to tales of mermaids and sirens.
18:36They are sea cows and manatees.
18:40Today, these delightful creatures are a rare sight.
18:42Only three species remain, and there are only a few thousand of each.
18:48The excavations at Shark Tooth Hill reveal that in the past they were plentiful.
18:53Here, Larry Barnes has found fossils of manatees, some of them very similar to today's,
18:59and some of them very different.
19:01One of the really exciting things about discovering new kinds of fossils is that we can find things
19:06that are totally extinct. Take, for example, this animal, which is neither a sea lion nor a walrus.
19:11It had four upper tusks and two lower tusks, and this lineage became totally extinct of natural
19:17causes at about six million years ago. Today we have left only sea lions and only walruses,
19:22so this is a totally unique kind of animal that we would not know about unless we studied fossils.
19:30Many mysteries related to the evolution of land mammals into sea mammals still remain.
19:37Their bodies had to have undergone monumental adaptations to allow them to eventually stand
19:42the atmospheric pressure of deep ocean diving.
19:46When a mammal or reptile unused to underwater pressure rises too quickly from deep water,
19:52they will get what is known as the bends, or decompression sickness. Modern whales never
19:58get the bends. Their bodies are fully adapted.
20:06With the use of cat scan and x-ray technology, scientists have discovered something that the
20:11naked eye could never. Cat scans of fossils have revealed that primitive whales and reptiles
20:18did indeed suffer from decompression sickness.
20:22We found, by accident, that mosasaurs, marine lizards that died about 65 million years ago,
20:29developed bends. It then turned out that within a specific genera, within a specific group,
20:36every single animal developed it. The question is, when did the modification take place that protected
20:42from the bends? Bends is certainly not helpful to survival. And so we started looking at this
20:47question in other marine animals and contemporary animals. The most classic area of investigation
20:53would be whales. And we hope to answer the question, did whales have bends? If they did,
20:58when they developed bends? And by analogy, when they started deep diving? And when they developed
21:04the modification that protected them from the bends?
21:09This fledgling study of decompression sickness in whales is growing rapidly. It won't be long before
21:15scientists will be able to determine the exact whale species that was the first to be fully adapted
21:20to life in the seas. By 1861, just two years after Charles Darwin published The Origin of Species,
21:30his bear-to-whale hypothesis quietly disappeared from subsequent additions. Scientists today admit
21:37that Darwin's unsupported speculation was not very scientific. First of all, I wouldn't dignify
21:43Darwin's swimming bear speculation with the name theory. It's not a theory. It's one paragraph that he
21:48wrote as a throwaway in The Origin of Species. It was an egregious speculation. And he got a lot of
21:56flack
21:56for it, as he should have, because it was a silly speculation. Not necessarily false, just silly. It had no
22:00evidence to support it.
22:03Yet Darwin's idea of a land animal evolving into a whale had been amazingly accurate. The only difference
22:10was that instead of a bear, whales evolved from wolf-like creatures.
22:15For scientists, it has been clear for a long time that whales had land ancestors and that therefore,
22:20somewhere, there must have been these transitional forms. It's nice to now actually have the real fossils,
22:26so one can show some of the skeptics that these animals actually existed, these animals that scientists
22:32had dreamed up for over a century, that they were actually there. The real fossils have now been found.
22:39If you're satisfied with a story you make up about how transitions like this happen, fine. I'm not. I've always
22:48been more interested in finding the evidence in letting, as it were, the fossils or the earth speak
22:54to me as opposed to trying to impose some idea I have about it. And to me that's the exciting
23:01thing
23:01about these fossil whales we're finding, is I feel like this is a story that the earth is telling us
23:07as opposed to something we're forced to sit back and make up.
23:16The story of how whales return to the sea is an extraordinary tale. Who would have believed
23:23that a fish would grow legs, crawl out of the sea, and turn into a staggering variety of creatures,
23:29among them the dinosaurs? More extraordinary yet, that an animal would millions of years later shed its
23:37legs return to the sea and grow to be the largest creature that ever lived. But they did.
23:47In an evolutionary leap that seemed impossible, they'd gone back to the sea.
24:07So
24:23you
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