- 7 weeks ago
Documentary, When Whales Walked Journeys In Deep Time (2019)
A deep dive into the evolutionary history of whales, elephants, crocodiles and birds.
Discover the evolutionary secrets of some of the world’s most majestic creatures. From voracious crocodiles and acrobatic birds to stupendous whales and majestic elephants, WHEN WHALES WALKED follows top scientists from around the world on a global adventure as they follow clues from the fossil record and change what we thought we knew about the evolution of iconic beasts.
A deep dive into the evolutionary history of whales, elephants, crocodiles and birds.
Discover the evolutionary secrets of some of the world’s most majestic creatures. From voracious crocodiles and acrobatic birds to stupendous whales and majestic elephants, WHEN WHALES WALKED follows top scientists from around the world on a global adventure as they follow clues from the fossil record and change what we thought we knew about the evolution of iconic beasts.
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AnimalsTranscript
00:00:03I was taken out to this site in the middle of the desert. I had no idea what awaited me.
00:00:11And then I saw them. I just started crying. These trackways in the Arabian desert are
00:00:19footprints in time. They were made seven million years ago by prehistoric elephants.
00:00:29They take us back to a bygone world and its vanished creatures.
00:00:37How did elephants from so long ago give rise to the magnificent animals we know today?
00:00:44How did any of the animals in this African landscape become what they are?
00:00:51For generations, it was a mystery.
00:00:53Now scientists are revealing the answers. Piecing together an epic story. This film unlocks
00:01:03the evolution of four of the world's most spectacular creatures. Crocodiles, birds, whales, and elephants.
00:01:16Like every animal alive today, they have a deep time history. A lineage full of twists and turns,
00:01:25shaped by strange ancestors from long ago. Bizarre ancient crocs.
00:01:33This thing was built like a greyhound.
00:01:36Feathered dinosaurs. Feathered dinosaurs. Dinosaurs never went extinct. In fact, birds are dinosaurs.
00:01:42A whale ancestor that lived on land.
00:01:45It more looks like a dog with a long snout.
00:01:48It's a story millions of years in the making of lost creatures rediscovered and the surprising lessons
00:01:57of deep time.
00:02:25Madagascar.
00:02:26Madagascar.
00:02:28250 miles off the coast of Africa, this island is a perfect laboratory for the study of evolutionary
00:02:36change. Isolated here for millions of years, species have transformed in unique ways. Scientists
00:02:47have long studied the evolution of the island's chameleons, bats, and lemurs. Now, the search is on for the ancient
00:02:56history of one of Earth's strangest animals. The crocodile.
00:03:15In flooded underground caves, researchers are looking for the remains of an extinct croc species.
00:03:23It may have disappeared just 2,000 years ago. A recent twist in the story of crocs.
00:03:31Madagascar.
00:03:32Some people see crocodiles as this animal that's unchanging through time. And actually, we know now that that's not true,
00:03:38but they look like it.
00:03:47But strangely beautiful. The 14 living crocodile species are all very similar.
00:03:55Madagascar.
00:03:57Most of the living species of crocodile are really, really hard to tell apart unless you're somebody who spends all
00:04:04your time thinking about crocodiles, like me.
00:04:09They all have the same reptilian mean!
00:04:12They all have the same reptilian body plan. Low to the ground and armored from head to toe in thick
00:04:21scales.
00:04:24They seem like living fossils. Some hangover from the age of dinosaurs. But are they?
00:04:35is this really an animal frozen in time perhaps the mysterious species in the
00:04:44cave will provide some answers about recent crocodile evolution so there's
00:04:52this crocodile that existed on the island of Madagascar until relatively
00:04:57recently and it disappears about the same time that humans got here and that
00:05:02crocodile was called the Horned Crocodile of Madagascar so one of the big
00:05:07questions is what was that crocodile who were its relatives and what happened
00:05:12to it it's one of the biggest mysteries
00:05:20today there is only one species on Madagascar the famous Nile crocodile
00:05:32one of the fiercest of Africa's predators
00:05:46scientists think it squeezed out the smaller horned croc but there's a lot
00:05:55there may be answers in the flooded caves
00:06:05I knew from speaking with some other people that there were supposedly crocodile skulls in this cave
00:06:14of this species that no one has seen for at least 200 years but more likely a thousand years
00:06:26a half-hour in they see it a skull
00:06:47so excited a skull yeah look at that that's beautiful
00:06:52so excited a skull yeah look at that that's beautiful
00:07:03so it's a very interesting horned crocodile of Madagascar and when researchers first started coming to Madagascar from Europe
00:07:09they saw these crocodile skulls and they weren't sure exactly what they were they
00:07:14didn't look exactly like now crocodiles they realize it was a separate species
00:07:20if Yvonne's lucky she'll be able to extract its DNA and learn where the horned croc fits into the story
00:07:28of crocodile evolution
00:07:32to meet the very first crocs we must trace one branch of the vast tree of life far back in
00:07:40deep time
00:07:40230 million years into the geologic period called the Triassic
00:07:49it's hard to imagine such a vast expanse of time
00:07:54if you look for instance at your historical time you can think back to your grandparents and that time frame
00:08:01that people are still comfortable with
00:08:04but you go further back go say back thousands of years when much of North America was covered by ice
00:08:10a very different world but go further back yet go back to a hundred million years and this world would
00:08:18have been entirely unrecognizable
00:08:20would have been like going to another planet and seeing life forms that were for the most part utterly alien
00:08:27to our experience
00:08:28and this is really difficult to grasp
00:08:32there is little about the planet of the Triassic we would recognize
00:08:39the continents we know today had not yet formed
00:08:43they were all contained in one huge land mass surrounded by water
00:08:50Pangea
00:08:53it was here along with the dinosaurs that the first crocs evolved
00:09:00in the beginning they were even more successful than the dinosaurs
00:09:05and to our eyes they look totally bizarre
00:09:11well the Triassic was in many ways actually the age of crocodiles
00:09:14and in any Triassic landscape
00:09:17you would have seen this vast diversity of crocodile relatives with many body forms
00:09:24Anjan Buller has been unearthing the bones of the very first crocodile relatives
00:09:29two of them were found together near some sandstone cliffs in southern Utah
00:09:38well these are two of the most extraordinary skeletons from the crocodile line that have ever been found
00:09:46this large animal here is something called a Popasaur
00:09:50it is the only complete skeleton of one of these animals that's ever been found
00:09:55all the subtle features on it I mean it's just
00:09:58it's the find of a lifetime
00:10:01these animals show us what crocodiles were like
00:10:05at the beginning of their evolution
00:10:09and they're very very different
00:10:12the extraordinary thing about this animal
00:10:14is that it was really trying to be a dinosaur
00:10:17before dinosaurs were dominant
00:10:19in that it was actually walking around on two legs
00:10:22you see how large and how heavily built the legs of this animal are
00:10:27compared these tiny little arms
00:10:30and so this animal couldn't rest any of its weight on its arms
00:10:36Popasaurus was a fierce, fast moving land predator
00:10:40acting for all the world like a dinosaur
00:10:45and it wasn't the only strange Triassic croc to be found in Utah
00:10:51in fact the Popasaur, this large skeleton
00:10:54was the first thing we found
00:10:56and we dug out this big skeleton
00:10:57then right underneath it was a tiny foot
00:11:02and underneath that foot was this animal here
00:11:06which is the only complete specimen of what we call a sphenosuchian grade stem crocodile that's ever been found
00:11:15they called the sphenosuchian little foot
00:11:18it was even stranger than Popasaurus
00:11:22and so the Popasaur is something like a mountain lion
00:11:25whereas the sphenosuchian
00:11:27you look at this animal
00:11:29and it's got a slender little body
00:11:31it's got extraordinarily long legs
00:11:34extraordinarily long arms
00:11:35and these arms were taking its weight
00:11:37unlike those of the Popasaur
00:11:39and so this thing was built almost like a greyhound
00:11:42with a heavy head and a long tail
00:11:45it was an animal that was utterly built for speed
00:11:52The strange creatures of the Triassic
00:11:55were part of the first great flowery of the crocodile family tree
00:12:00but 200 million years ago
00:12:03much of that tree was cut back
00:12:07when a mass extinction wiped out the vast majority of the animals of land and sea
00:12:16as the supercontinent Pangaea began to break up
00:12:20volcanoes pumped vast amounts of carbon dioxide into the air
00:12:25acidifying the oceans
00:12:27the planet warmed
00:12:29and habitats were transformed
00:12:33most of the Triassic crocodile relatives
00:12:36including Popasaurus and Littlefoot
00:12:39died out
00:12:40Extinctions are of great interest to evolutionary biologists
00:12:45because they basically reset the evolutionary game
00:12:50every once in a while during the history of life
00:12:53there have been catastrophic events of such magnitude
00:12:57that thousands or millions of species were wiped out
00:13:01in what basically in deep time is a single moment
00:13:05There have been five major extinctions in Earth's history
00:13:09Through the lens of deep time
00:13:11we can see they caused profound destruction
00:13:14and changed the history of life on Earth
00:13:20the mass extinction that ended the Triassic period
00:13:24ushered in a new chapter in the story of Crocs
00:13:28in the Jurassic and Cretaceous periods
00:13:31Crocs flourished again
00:13:33but in new and even stranger ways
00:13:39a record of those wondrous creatures is preserved in one of the most spectacular landscapes on Earth
00:13:48Patagonia
00:13:53many groups diversified in the Jurassic
00:13:56dinosaurs were certainly the most conspicuous
00:14:00because they were big
00:14:01but other groups began to diversify in a very very impressive way
00:14:05and Crocs were one of them
00:14:08For the duration of the Jurassic and Cretaceous periods
00:14:12almost 150 million years
00:14:15Crocs vied with dinosaurs for dominance
00:14:20They stopped being only the land animals they were in the Triassic
00:14:25and experimented with radically new ways of being
00:14:30You start seeing animals like Dacosaurus
00:14:34It's a swimming marine croc
00:14:36that adapted their forelimbs into paddle-like flippers
00:14:40and then you have freshwater gigantic crocs like Sarcosuchus
00:14:45that's about 12 meters long
00:14:48it was eating dinosaurs
00:14:50and then you have herbivorous crocs like Nodosuchus
00:14:54Look at this animal
00:14:55It really looks nothing like a croc
00:14:58It has a short snout, very high
00:15:01the eye sockets are pointing to the sides
00:15:04and the crazy, crazy thing is that
00:15:07it moved the lower jaw back and forth
00:15:10and this was a way of the upper teeth and the lower teeth
00:15:14to slide against each other
00:15:17and in that way this animal was processing the plant matter
00:15:22So here was an ancient croc
00:15:24that chewed like a goat
00:15:31Diego has spent much of the last 20 years excavating ancient crocs
00:15:36from the barren outcrops of Patagonia
00:15:41But back when those creatures lived
00:15:44the world was a very different place
00:15:47It was a much warmer planet
00:15:50there were no ice caps on the poles
00:15:55In the warming greenhouse world of the Jurassic and Cretaceous
00:16:00crocs prospered
00:16:02This was their golden age
00:16:06They became so diverse that in some places you go
00:16:10and you basically only find crocs
00:16:12So we can see a really, really crazy diversity in the Cretaceous
00:16:16and then about 66 million years ago
00:16:20it all went away
00:16:24What happened to the many Cretaceous crocs?
00:16:29It seems most of them perished the same way as the dinosaurs
00:16:36It was long realized that around 66 million years ago
00:16:40there was a major extinction of animals and plants
00:16:43on land and in the oceans
00:16:45On land the most famous casualty was the dinosaurs
00:16:57Scientists agree that an asteroid strike brought on the global devastation
00:17:02But many now argue it was not the only cause of the mass extinction
00:17:07From the fossil record, they can see that climate changes
00:17:11were already pushing many species to extinction
00:17:15before the asteroid impact
00:17:18So basically this impact is sort of thought
00:17:21if not the sole cause of the extinction
00:17:24certainly the coup de grace for a great many lineages
00:17:30Ancient crocs were reduced to a fraction of what they once had been
00:17:36So out of this wonderful diversity
00:17:39only few species made it through
00:17:42And the ones that actually made it through
00:17:46were very particular in many ways
00:17:50They were certainly adapted to living in a freshwater environment
00:17:54They were adapted to feeding in water
00:17:58They were predators
00:18:00They were not herbivores
00:18:02because they were not land crocodiles
00:18:04They were not marine crocodiles
00:18:05So only a tiny fraction of that diversity made it through
00:18:10The crocodiles that made it through
00:18:12were the shoreline predators that lived half in water
00:18:16and half on land
00:18:20Their low tank-like body plan may have been one secret of their survival
00:18:27It allows them to lie semi-submerged in the shallows
00:18:31and ambush their prey with ferocious speed
00:18:40The success of that lethal design
00:18:43is why crocodiles today all seem so similar
00:18:51Crocodiles have this form that's very, very successful
00:18:54They have sort of an armored body plan
00:18:57that allows them to be a successful predator
00:19:01in aquatic environments
00:19:02Aquatic environments can be more stable
00:19:05than other kinds of environments
00:19:06like terrestrial environments
00:19:07And so it makes sense that they've retained this body plan
00:19:11from deep time
00:19:12from the ancestral crocodilians
00:19:13that were around the globe millions of years ago
00:19:16It works really well
00:19:18Why change it?
00:19:21Of course, that classic body plan
00:19:24is no guarantee of survival
00:19:28The horned crock of Madagascar
00:19:30died out just centuries ago
00:19:32likely pushed out by the giant Nile crock
00:19:41Results from Yvonne's work
00:19:43suggest the species are more closely related
00:19:47than anybody realized
00:19:55It's a great example of how DNA analysis
00:19:58has become a vital tool for paleontologists
00:20:06One of the exciting things about the new toolkit we have today
00:20:09the ability to use DNA to look at evolutionary history
00:20:13is we can use it as sort of a metric for change over time and lineages
00:20:17So, with living species we can take their DNA
00:20:20and we can calculate back how long it takes
00:20:24to accumulate the number of changes we see in the genome
00:20:28and we can say
00:20:29this corresponds to a split 3 million years ago
00:20:34or 6 million years ago
00:20:35or 20 million years ago
00:20:38DNA has shown that both crocodiles and alligators
00:20:42are descended from a common ancestor that lived 80 million years ago
00:20:49and then even more recently
00:20:51this thing that we've always thought is the sort of primordial crocodile
00:20:55the Nile crocodile
00:20:56we recently have found using molecular clock dating
00:21:00that the Nile crocodile is just a baby
00:21:03it just arose probably within the last 4 to 6 million years
00:21:07it's a young'un on the landscape of crocodilians in the modern world
00:21:15so despite their prehistoric appearance
00:21:18it turns out that over their 230 million year history
00:21:23crocodiles have been in constant evolution
00:21:29they have proved themselves to be one of the most resilient lineages
00:21:33on the face of the planet
00:21:36for me these crocodiles sort of represent an organism that
00:21:42through the history of life on earth
00:21:44it's found a way to persist
00:21:47the story of the crocodile lineage
00:21:50is of deep time transformations
00:21:52that produced a wild diversity of croc species
00:21:56followed by a steep decline
00:22:00today there are just a handful of crocs
00:22:03and the strange animals that gave rise to them
00:22:06are all gone
00:22:10the surviving crocs are all very similar
00:22:14all shoreline predators of the tropics
00:22:20but while the crocodile lineage has bottlenecked
00:22:24another lineage is experiencing a wild explosion of diversity
00:22:55birds have colonized every environment on earth
00:23:00and they come in an astonishing variety of shapes, colors, and sizes
00:23:07they're more species of birds than any other group of vertebrates that lives on land
00:23:16they can cross the Himalayas on wing
00:23:20they can dive into a part of the ocean where sunlight does not reach
00:23:28they can migrate between continents
00:23:30they can migrate between continents
00:23:32so they are truly remarkable
00:23:37birds have colonized not only the natural environments of the planet
00:23:42but also the urban spaces created by humans
00:23:47there are more than 10,000 species of birds
00:23:50there are more than 10,000 species of birds
00:23:50but even more striking than that
00:23:52there are more than half that number
00:23:55is just within one lineage
00:23:58songbirds
00:23:59so that means that the birds that are in your backyard
00:24:01are part of what is truly an extraordinary evolution
00:24:08so what's the story behind the spread of birds across the planet?
00:24:13how did they come to be everywhere and so diverse?
00:24:20things that can seem so commonplace
00:24:22crows or pigeons in a park
00:24:24are the leavings of an amazing history
00:24:28that stretches back hundreds of millions of years
00:24:33our understanding of that evolutionary history
00:24:37began with one extraordinary fossil
00:24:40discovered in the 1860s in Germany
00:24:44Archaeopteryx
00:24:47this fossil to many people might just look like roadkill
00:24:51or something that hit your window
00:24:54but in fact to me
00:24:56these bones they come to life
00:24:59and the wings are moving
00:25:02covered in feathers
00:25:04but with mobile claws at their tips
00:25:07most striking is a long bony tail with feathers
00:25:14150 million years old
00:25:17Archaeopteryx was a bird
00:25:19it had feathers and it could fly
00:25:22but with its claws tail and toothed beak
00:25:25there was something almost dinosaur-like about it
00:25:29it led proponents of the new theory of evolution
00:25:33to make a sensational claim
00:25:36birds must have evolved from dinosaurs
00:25:41when I look at this I see an icon of evolution
00:25:44it was one of the first key
00:25:48and totally unavoidable pieces of evidence
00:25:52consistent with evolution
00:25:54but the theory that birds evolved from dinosaurs
00:25:58met intense opposition
00:26:00how could something so huge and heavy
00:26:03evolve into something so small and light
00:26:08one of the biggest objections
00:26:10was that no dinosaur had ever been found with a wishbone
00:26:14in birds
00:26:16the crucial brace for the chest that makes flight possible
00:26:22the search was on
00:26:23if scientists could find a dinosaur with a wishbone
00:26:27they would clinch the case
00:26:31but for a century
00:26:32they failed
00:26:40then in the 1960s
00:26:44paleontologist John Ostrom
00:26:46hit paydirt
00:26:50a dinosaur fossil
00:26:52with a wishbone
00:26:56he called it Deinonychus
00:26:58terrible claw
00:27:01here we have Deinonychus anterophus
00:27:04the fossil that changed everything that we know about the origin of birds
00:27:09and fundamentally altered our understanding of how flight evolved
00:27:16Deinonychus was a ferocious predator
00:27:18with wing-like arms and all the bones and muscles necessary for flight
00:27:24but it couldn't fly
00:27:27here's an animal with four limbs
00:27:29much too short
00:27:30and much too heavy in the body
00:27:32to be able to fly
00:27:33yet it has all the bells and whistles
00:27:36that we associate with the flight stroke
00:27:42not only that
00:27:43it had feathers too
00:27:47but all this had nothing to do with flight
00:27:50its feathers were for warmth
00:27:54and its clawed wings were for killing
00:28:03the arms up against the body
00:28:05and you shoot it down and forward
00:28:07grab your prey
00:28:08drag it up and back
00:28:10down and forward
00:28:11up and back
00:28:12down and forward
00:28:12up and back
00:28:13that's the flight stroke
00:28:15so all the details
00:28:17the basic architecture at least
00:28:20of the flight stroke
00:28:21is an evolved
00:28:22and an animal
00:28:23that is not using it to fly
00:28:28amazingly
00:28:29these tools built for killing
00:28:33would eventually power flight
00:28:38so you have feathers
00:28:39and you have the flight stroke
00:28:41colliding in one animal
00:28:43so the skies were no longer a barrier
00:28:46to the evolution of dinosaurs
00:28:48and that's why we think that birds are living dinosaurs
00:28:56Deinonychus was powerful evidence that dinosaurs gave rise to birds
00:29:01but the many stages of that evolution were still unknown
00:29:05to complete the story
00:29:08scientists needed more fossils
00:29:14another long wait began
00:29:22then in the 1990s
00:29:24farmers in a remote province of northeastern China
00:29:28blew the story of bird evolution
00:29:30wide open
00:29:34they had been turning up rocks
00:29:36with the outlines of birds in them
00:29:38for as long as they could remember
00:29:43they had no idea
00:29:44these were the bird dinosaur fossils
00:29:47scientists had been waiting for
00:29:57by the late 1990s
00:29:59fossil fever had broken out
00:30:01in Liaoning province
00:30:05at first nobody knew how valuable they were
00:30:11but then we found out
00:30:12we all started to dig
00:30:14I did too
00:30:17I found something that looked like a bird
00:30:19I didn't know what it was
00:30:21but they said it was something called
00:30:22Confucius ornus
00:30:25a single fossil could bring a year's income
00:30:29as farmers scoured the landscape
00:30:31the fossils started to pour in
00:30:35hundreds of ancient birds from the time of the dinosaurs
00:30:40the fossils from western Liaoning
00:30:43started to show us
00:30:44the transitional forms
00:30:45they showed us the earliest birds with beaks
00:30:48the earliest birds with short tails
00:30:50like living birds
00:30:52bird fossils are extremely rare
00:30:55because bird bones are so delicate
00:30:57but here in northeastern China
00:31:00a hundred and thirty million years ago
00:31:03a unique combination of circumstances created the perfect conditions
00:31:09for their preservation
00:31:12if you were able to come back here
00:31:14a hundred and thirty one to a hundred and twenty million years ago
00:31:17and looked out
00:31:18you would have seen lakes as far as the eye could see
00:31:21with active volcanoes going off around them
00:31:24and a forested environment growing by the shores of these lakes
00:31:28and this forest would have been teeming with small feathered dinosaurs
00:31:33as those small feathered dinosaurs died
00:31:36and fell or were washed into lakes
00:31:39they were quickly buried in layers of volcanic ash
00:31:49the result?
00:31:51an extraordinary record of Cretaceous bird dinosaurs
00:31:56perfectly preserved in stone
00:32:01the amazing thing about these fossils
00:32:04is the exceptional preservation of soft tissues
00:32:07which revealed these extinct animals
00:32:10in a level of detail that we paleontologists
00:32:13never previously thought possible
00:32:16fossilized along with the birds
00:32:19were plants and seeds
00:32:20allowing scientists to reconstruct the forested environment of the time
00:32:26together
00:32:28the wealth of Liaoning fossils
00:32:30reveal a world where creatures representing
00:32:33every stage of dinosaur to bird evolution
00:32:37lived side by side
00:32:40they show how nature experimented with every aspect of what would finally make a bird
00:32:48beaks, wings, feathers, and flight
00:32:54there was Chaudipteryx
00:32:56a small feathered dinosaur that had wings
00:33:00but couldn't fly
00:33:02living alongside it were creatures that flew
00:33:05but still had many dinosaur characteristics
00:33:09teeth, long tails, and claws on their wings
00:33:13and there were creatures like Confucius sorenus
00:33:17almost identical to modern birds
00:33:23the feathered dinosaurs of Liaoning
00:33:26are a reminder that evolution does not move in a straight line
00:33:32there's a common perception that evolution proceeds in a very linear fashion
00:33:37so you have a little dinosaur that somehow decides
00:33:41to become a bird
00:33:44but actually the many bird features were gradually acquired
00:33:49there were a lot of dead ends in this evolutionary process
00:33:54just like Deinonychus
00:33:56the Liaoning fossils show that wings and feathers evolved separately
00:34:01and for reasons that have nothing to do with flight
00:34:12it was only after millions of years
00:34:15that these things came together
00:34:17to make the creature we call a bird
00:34:23in fact what we've learned from this huge diversity of fossils
00:34:27is that these features that we associate with modern birds
00:34:29actually evolved multiple times
00:34:34the Liaoning fossils opened a window
00:34:37on the profusion of feathered dinosaurs that populated the whole world
00:34:42many millions of years ago
00:34:46what happened to them all?
00:34:49most died out in the same extinction event that killed the big terrestrial dinosaurs and most crocs
00:34:59but like the crocs
00:35:01but like the crocs
00:35:01a few birds squeaked through
00:35:05those few survivors gave rise to all the birds on earth today
00:35:11but how did that amazing story of survival play out?
00:35:16remarkably, scientists are solving that mystery
00:35:19not from bones, but from DNA
00:35:23so what happened is that this mass extinction occurs
00:35:26maybe as a result of a big giant meteorite
00:35:29and climate change and so forth
00:35:30a few groups of birds survive
00:35:33only 5% of the species survive
00:35:39Eric and his colleagues compared the genomes of different bird species to calculate their degrees of similarity
00:35:47they could then figure out when they last shared common ancestors
00:35:53first thing we figured out is that those ones that survived
00:35:57the deepest branches in the tree that we generated
00:36:00were the ones that were shorebirds
00:36:02that can survive in water, that can survive in land, that can survive in different habitats
00:36:08along with shorebirds like ducks and geese
00:36:11the ancestors of ostriches and emus also survived
00:36:17then those few 4 or 5 lineages that survived
00:36:21in a 15 million year window
00:36:23gave rise to every species that we are looking at now today
00:36:30scientists are finally in a position to see the whole vast avian tree of life
00:36:39arising with the dinosaurs
00:36:41the bird lineage experimented for millions of years with feathers, beaks and wings
00:36:48it barely survived a major extinction event
00:36:52before finally flowering in the 10,000 species alive today
00:37:05but while the bird lineage exploded and birds colonized every habitat on earth
00:37:11another lineage concentrated on colonizing just the seas
00:37:28for as long as humans have known them
00:37:30whales have inspired fear and wonder
00:37:36how could these giants of the deep have grown so huge
00:37:42how could air-breathing creatures like us have come to live in the depths of the ocean
00:37:56what science now knows about these leviathans of the deep is amazing
00:38:05bowhead whales can live for up to 200 years
00:38:10longer than any other mammal on earth
00:38:15sperm whales can dive to depths of over 3,000 feet
00:38:20and stay underwater for an hour and a half without breathing
00:38:30blue whales are the biggest creatures to ever have lived on earth
00:38:36bigger than even the largest dinosaurs
00:38:38bigger than even the largest dinosaurs
00:38:45up to 100 feet long and 200 tons in weight
00:38:49they have a heart the size of a small car
00:38:54and these giants of the deep sing to each other
00:38:57communicating over vast distances in a language of song
00:39:02that researchers still don't fully understand
00:39:10how did these gargantuan animals and their remarkable behavior evolve
00:39:18for so long it was a mystery
00:39:23we've known that their whales are mammals since the 18th and 19th centuries
00:39:28because they're warm-blooded and they suckled their young
00:39:31but we didn't know where they came from
00:39:46Darwin talked about the origin of whales in his classic book The Origin of Species
00:39:51where he said someone he knew had observed a bear swimming around skimming insects off the surface of the water
00:39:58and he suggested that perhaps something like a bear could have evolved into a whale
00:40:03the kind of whale that filter feeds
00:40:05by doing something similar and getting better and better at it over time
00:40:11Darwin was not correct about that
00:40:14but at least he could conceptualize of a way that whales had evolved
00:40:18but basically we didn't know where whales came from until extremely recently
00:40:26the fascination with whale evolution began in the 19th century
00:40:33stories of sea monsters filled the popular imagination
00:40:39when the first fossil whale was unearthed
00:40:43its discoverers thought they'd found a gigantic sea serpent
00:40:47it was called Basilosaurus
00:40:51was discovered in North America along the Gulf Coast in the 1830s
00:40:56and it was actually the first fossil whale ever to be scientifically named and studied
00:41:01the gentleman named it a man named Harlan
00:41:04it read about large sea serpents being discovered elsewhere in the world
00:41:09and so he thought that this was something similar
00:41:11and thus he named this animal Basilosaurus which means King Lizard
00:41:19in the 1840s
00:41:20up to 50 feet long with ferocious teeth
00:41:23Basilosaurus was a formidable marine predator
00:41:29finally in 1841
00:41:31it was identified as a whale
00:41:34and dated to about 35 million years ago
00:41:38for almost a century after its discovery
00:41:41Basilosaurus remained the oldest known whale
00:41:44whale
00:41:45it was assumed to be the ancestor of all living whales
00:41:50so after the discovery of Basilosaurus
00:41:53there were other whales found
00:41:54that were just a little bit earlier and more primitive
00:41:58but not by very much
00:41:59maybe 5 million years older than Basilosaurus
00:42:02and it didn't push the origin back in time
00:42:05and we really didn't discover a whole lot more about the origin of whales
00:42:12the deep origins of the whale lineage were a mystery until 1975
00:42:18when a paleontologist went on a fossil hunting expedition to Pakistan
00:42:25he wasn't looking for early whales at all
00:42:29I was interested in how archaic mammals changed into modern mammals
00:42:34things like the first horses
00:42:36that's what I was interested in
00:42:38I took several students with me and colleagues from Paris
00:42:42and we looked first in Punjab province
00:42:46then south in Sindh
00:42:47we still hadn't found anything very interesting
00:42:50and we went to the northwest frontier province
00:42:53and there high on a hill
00:42:55we found a little jaw of a land mammal
00:43:00later they found a piece of skull
00:43:02and its strange ear bones finally unlocked the secrets of early whale evolution
00:43:10this is what was left
00:43:12the back of a skull
00:43:13and if you look at the underside
00:43:16it has the covering of the ear on the right side
00:43:21and that covering is missing on the left side
00:43:25those ear bones turned out to be the key
00:43:29Philip thought he was looking at the skull of something like a primitive deer
00:43:33but it unmistakably had the ear bones of a whale
00:43:41whales have a special structure of the ear to be able to hear in water
00:43:46it turns out that they effectively see in water by using sound
00:43:51and so to do this the ears have become modified
00:43:59the ear bones of whales are very dense
00:44:01and that density helps them to hear sound in the water
00:44:06mammal ears originally evolved in terrestrial animals
00:44:11and so their structure is optimal for hearing in air
00:44:17and in water sound behaves really differently
00:44:21so for example if you go into a pool
00:44:24or under a lake you can hear sound but it's a little muffled
00:44:28but the one thing you can't do is you can't figure out where the sound is coming from around you
00:44:32and that's because the way mammals do this is they use the difference in time
00:44:37between when a sound hits your right ear and your left ear
00:44:41to figure out what direction the sound is coming from
00:44:44so if a sound is off to my right
00:44:46it hits my right ear first
00:44:47then my left ear and so my brain says the sound is over to my right
00:44:51but in water the tissue of your face and skull is about the same density as water
00:44:58so the sound rather than going around my skull to my left ear goes right through it
00:45:04so it gets to my left ear at almost the same time as my right ear
00:45:08and I can't tell where the sound is coming from
00:45:11so the added density to whale ears is reestablishing their ability to hear directionally underwater
00:45:18Philip's fossil had that same distinctive ear and it was 49 million years old
00:45:25that could only mean one thing
00:45:28here at last was one of the very first whales
00:45:32Philip named it Pachycetus
00:45:37once we knew it was a whale we knew it was the oldest whale anyone had ever found
00:45:43Pachycetus pushed the origins of whales back 15 million years
00:45:48to the time when the Indian subcontinent was slowly crashing into Asia
00:45:55where Pachycetus was found was once an ocean shoreline
00:46:00its ears made it clear Pachycetus spent time underwater
00:46:07but other fragments of skeleton also clearly showed it walked on four legs
00:46:13how did this strange beast give rise to the giants we know today
00:46:28at the Museum of Natural History in Paris one of the birth places of paleontology
00:46:34they have been assembling the skeletons of prehistoric animals for over 200 years
00:46:46they now have one of the few complete reconstructions of the extraordinary whale ancestor Pachycetus
00:46:57you see it's a quadrupedal animal with the higher forelimbs and hind limbs
00:47:01it means that this animal was definitely partly terrestrial
00:47:06and obviously it's quite a strange animal very small
00:47:09doesn't whale looking at all
00:47:12it more looks like a dog with a long snout
00:47:17Pachycetus is one of the strangest surprises of evolution
00:47:22a whale ancestor that looks like a small wolf with webbed feet for swimming
00:47:29the key thing about it is it has elongated finger and toe bones
00:47:35so clearly it's already semi-aquatic
00:47:45Pachycetus was a creature of the shoreline
00:47:49hunting for fish and perhaps other small animals in the shallows
00:47:55and we think that it was using its longer snout
00:47:58to probe for aquatic prey in the water
00:48:01and so it was feeding in the water
00:48:03while almost certainly going out on land to breed and have their young
00:48:09once they adapted to life in the shallows
00:48:12it took 10 million years for the descendants of Pachycetus to become fully aquatic
00:48:20why did it take so long?
00:48:23because to live underwater they had to change
00:48:29it is one of the most remarkable stories of total physical transformation in the annals of evolution
00:48:41after Pachycetus
00:48:43whales take about 10 to 12 million years to evolve into fully aquatic forms
00:48:48and during that time their hind limbs tend to get smaller
00:48:53their skulls tend to get longer
00:48:55and the nares which is the hole in the skull
00:48:58where the nose is moves up the skull
00:49:02in addition their forelimbs tend to turn into flippers
00:49:06and they get more vertebrae in their back which makes their bodies longer
00:49:13but there was still one great transformation to take place in whales
00:49:19baleen feeding
00:49:22so near the base of the whale family tree there's this major split into the two groups that we have
00:49:27today
00:49:28we have toothed whales and then we have baleen whales that actually lose their teeth entirely
00:49:33and they grow what are called baleen plates that are made of keratin
00:49:36so they're actually more like hair or fingernails
00:49:40and these whales use it to filter their food
00:49:42so they'll take big gulps of water
00:49:45and they'll actually filter their prey little tiny microscopic organisms
00:49:49out of that water using the baleen plates
00:49:55the split into toothed whales like orcas and dolphins
00:49:59and baleen whales like blue whales and humpbacks
00:50:03happened about 30 million years ago
00:50:09the toothed whales remained like their ancient ancestors
00:50:14predators living mostly in coastal waters
00:50:20there they could feed on fish
00:50:22or like some of the orcas, seals and baby sea lions
00:50:38the baleen feeders underwent a much greater transformation
00:50:45with a radically new way of filter feeding
00:50:49they moved into the deep oceans and became huge
00:50:57why?
00:51:00for a long time
00:51:01the massive size of some baleen whales was a puzzle
00:51:09but it turns out that in the ocean
00:51:11great size is an advantage
00:51:17if you look at the energy budget of these animals
00:51:20they use fewer calories per unit body mass when you get bigger
00:51:26and so they're more efficient when they're huge
00:51:30they're also more efficient when they move, when they swim
00:51:33at large body size
00:51:35so there's advantages to being large in the ocean
00:51:41the huge size of baleen whales is also linked to one of the last great planetary transformations
00:51:50Argentina and South America become completely separate from Antarctica
00:51:54and that changes the currents in the ocean system
00:51:57and it seems to really have a profound impact on what whales are doing
00:52:03the cold current that began to circle Antarctica
00:52:06led to a vast upsurge in the krill population that baleen whales feed on
00:52:13with large amounts of food and the efficient baleen filter feeding system
00:52:19there was simply nothing to stop baleen whales from becoming huge
00:52:29along with baleen
00:52:31whales have developed sophisticated fishing behaviors to trap their prey
00:52:38humpbacks rely on the help of gulls
00:52:44and what's happening is
00:52:46the diving birds are forcing the herring together
00:52:50that form a huge ball
00:52:52that gives the gulls at the surface a chance to propel themselves down
00:52:56and try to grab a herring
00:52:57and then somehow the humpbacks know that there's a concentration of feed there
00:53:04they come with their huge mouths, gulp it down
00:53:07get rid of the salt water through their baleen and swallow
00:53:11Jackie has been working with the humpback whale population off northern Vancouver Island for almost 20 years
00:53:21Jackie's work has led her to marvel at the delicate web of relationships linking humpbacks to every aspect of the
00:53:29marine ecosystem
00:53:32it's perfection, it's been going on longer than we can understand
00:53:38knowing whales keeps me in a state of humility and mystery
00:53:46which I think is how a human life is well lived
00:53:49it makes me feel connected
00:53:52it makes me feel appropriately small in the presence of giants
00:54:04over millions of years whales grew huge as they explored the seas
00:54:11but another mammal grew huge as it explored the earth
00:54:16evolving its own remarkable tools for life on land
00:54:31for millennia, these stately creatures have patrolled the African savannahs
00:54:37transforming the land as they go
00:54:40transforming the land as they go
00:55:07on these trails probably for hundreds of years
00:55:09they create paths that they then use for generations
00:55:24elephants are such extraordinary animals
00:55:26the more we learn about them
00:55:28the more we realize that
00:55:30we actually are only just scratching the surface
00:55:34every new discoveries emerge that elephants can understand things that we
00:55:38couldn't have dreamed possible
00:55:41and I think we'll never uncover their secrets
00:55:48Scientists have shown that elephants communicate through calls, touch, and even low-frequency vibrations
00:55:56which can travel underground for miles
00:56:01but there's still a lot that they don't fully understand
00:56:06it would be amazing if we could actually uncover what it is that they know
00:56:11I really think that we are blundering about right now
00:56:14because we don't even have the tools to measure how they communicate
00:56:19and Paula is certain that along with their ability to talk to each other
00:56:24they experience many of the same emotions we feel
00:56:28grief, anger, and empathy
00:56:33she senses a mysterious inner life
00:56:38when you sit with them for hours
00:56:39this like wealth of sensations just keep coming and coming and coming
00:56:44and it just seems to be endless
00:56:46I feel like I can really sense what is going on with those elephants
00:56:50and the longer I spend with elephants
00:56:52the more I feel in tune with them
00:56:57As much as she admires them
00:57:00Paula is keenly aware that elephants today are in trouble
00:57:06There used to be dozens of species of elephants
00:57:11and now there are just three
00:57:13and if we're not careful we will lose them as well
00:57:16and that will be the end of the lineage of elephants
00:57:20Could the ancient lineage of elephants really be coming to an end?
00:57:27How did these magnificent animals go from myriad species to just three today?
00:57:35And how did the ancient histories of humans and elephants become so intertwined?
00:57:48As with every lineage, it's a story that begins in deep time
00:57:54a story told by fossils
00:57:57most of them found in the birthplace of elephants
00:58:03Africa
00:58:06The deep origins of elephants lie in the Turkana Basin in northern Kenya
00:58:12In a place called Buluk, scientists are finding fossils that point to a magnificent age of elephants
00:58:24This is from the right side of the jaw
00:58:28Fossils are the messengers of the past
00:58:31I believe that
00:58:33I think that we as paleontologists are trying to be the interpreters of the messengers from the past
00:58:40They give you the opportunity to see the kind of incredible journey that elephants had to make to become elephants
00:58:48It took 60 million years to make an elephant
00:58:54Today, Buluk is one of the hottest, driest places on earth
00:58:59But 17 million years ago, it was a lush forest with rivers and wetlands
00:59:06It's a very wet climate
00:59:08It's a very equable climate, very warm climate
00:59:12It's a great place to be a browser
00:59:14It's a great place to go out and look for vegetation
00:59:17Great place to go get a salad
00:59:20Africa and the early Miocene
00:59:23How can scientists reconstruct those vanished environments?
00:59:27It turns out ancient landscapes leave traces just like ancient animals do
00:59:35We often find fossil wood and fossil seeds
00:59:40So that's telling us something about the environment
00:59:42And the red sediments around us are ancient soils
00:59:47They're actually ancient floodplain deposits
00:59:50So the animals would have been living out on these floodplains in these forested areas
00:59:56We're trying to reconstruct the whole environment that these animals were living in
01:00:01If you go in and just pick up the bones
01:00:03It's like taking the chocolate chips out of the cookies
01:00:07So we work with geologists and climate scientists
01:00:11And isotope specialists
01:00:12And all kinds of people, geochemists
01:00:16The painstaking work of Ellen and her colleagues
01:00:20Is allowing them to reconstruct the whole vanished world of ancient Baluk
01:00:27So if you were to be transported back to the early Miocene of Baluk 17 million years ago
01:00:34It would have been a mature meandering river system
01:00:38And a woodland
01:00:39And there would have been a whole host of different kinds of elephants
01:00:43So you would have had the dinotheres
01:00:45They're very, very primitive
01:00:47They're about a third or a half the size of a modern elephant
01:00:51And they would have been kind of snuffling along the riverbanks
01:00:54Because they seem to really like a closed canopy forest and a wet environment
01:00:59But at the same time, you have the amabilodonts, the shovel tuskers
01:01:04The lower incisors are these big long shovel-like tusks
01:01:08So they would have used them to scoop up their dinner
01:01:12As scientists excavate, they are astonished by the diversity of strange beasts they are discovering
01:01:26Ancient Baluk was a sort of Jurassic park of elephants
01:01:33Imagine I'm taking you on a safari
01:01:35But a safari back in time
01:01:37You'll be confronted with these magical creatures
01:01:40A slice of Africa that is now gone
01:01:43Or you'd be confronted here with amazing herds of elephants
01:01:50It would be mind-blowing to confront this scene
01:01:55I think the Miocene 16 million years ago at Baluk
01:02:01That would have been the center of the empire of the age of the elephants
01:02:10The ancient elephants here bear witness to a glorious flowering of the elephant lineage about 17 million years ago
01:02:20But what were their origins?
01:02:22And how did they come by their magnificent tusks and trunks?
01:02:28For decades, the earliest origins of the elephant lineage were a mystery
01:02:37But then, in the 1990s, a French paleontologist and his team were excavating in an abandoned phosphate mine in Morocco
01:02:47In layers dating to 56 million years ago, he came across fossil remains of a mysterious animal about the size
01:02:56of a small dog
01:02:57He called it Phosphatherium
01:03:02Later, he came across fragments of the jaws and teeth of an older, even smaller creature
01:03:08This one was no bigger than a rabbit
01:03:11As he puzzled over both fossils, he noticed something very strange
01:03:17Their teeth seemed to be miniature replicas of an elephant's teeth
01:03:22The more he looked, the more certain he became
01:03:26They must be ancestral elephants
01:03:29The oldest ever discovered
01:03:33It was an astonishing conclusion
01:03:36The oldest elephant ancestor was the size of a rabbit
01:03:45It's really amazing
01:03:47The fossils we found reveal the origins of Proboscidian evolution
01:03:52Which used to be totally unknown
01:03:55I give a lot of credit to my colleague Emmanuel Ghebrant
01:03:58Because it's like a detective story
01:04:00It's a real puzzler to figure out what they are
01:04:03And he found these things
01:04:04And he started looking at their teeth
01:04:06And he realized they had some subtle features on their molars
01:04:09The arrangement of the cusps on their molars
01:04:12That said, I am a Proboscidian
01:04:14Finally, scientists could see the very beginnings of the elephant evolutionary tree
01:04:25The key trait is the slow development of incisors at the front of the skull
01:04:32They are already starting to become enlarged in phosphotherium
01:04:37Those incisors just keep growing through all the stages of elephant evolution
01:04:43Right up to mammoths and modern elephants
01:04:48As incisors became tusks, they took on the functions they have in elephants today
01:04:56They're used for acquiring food, for knocking down plants so you can reach food
01:05:02They're used for social display
01:05:05Tusks are the defining features of elephants
01:05:08And it's like their behavior is tied up in having these tusks
01:05:13And as tusks grew, they propelled the evolution of the trunks that would become the hallmark of all later elephants
01:05:21So I think once you start to get tusks, then trunks follow that
01:05:25It is important because they have to have something to get past the tusks in order to reach the food
01:05:34in their environment
01:05:36As trunks grew, they slowly became the amazingly sensitive organ of touch and smell they are in modern elephants
01:05:48Trunks are made up of something like 72,000 tiny muscle fibers
01:05:53So they're highly complex and they can move them around the way that you can move your hand around playing
01:05:58the piano
01:05:59Elephants have tremendous control over their trunk
01:06:02It's not just flopping around and sucking up water
01:06:04They can really be very gentle
01:06:06They can pick a penny up off the ground with their trunk
01:06:10Those trunks get a big workout
01:06:17Tusks, trunks and great size were obviously successful elephant adaptations to their forest environment
01:06:26But they didn't just help elephants respond to their environment
01:06:30They gave them the capacity to change it too
01:06:35So I think of all the species that we know of, apart from humans
01:06:40The only other mammals that we know have the capacity to be able to alter the natural ecosystems
01:06:47They live in, in a short time, in a very big way, would be the elephants
01:06:56Proposidians are big animals and you can imagine any big animal going through a landscape
01:07:00Is knocking down trees, moving vegetation out of the way, creating paths
01:07:07For that, Bill believes we humans owe them a debt of gratitude
01:07:12He thinks elephants helped create the perfect conditions
01:07:17For a certain group of apes, millions of years later, to come down out of the trees
01:07:24And begin to explore the savannahs
01:07:28Those were our ancestors, the Australopithecines
01:07:32The famous early human Lucy was discovered not far from Baluk
01:07:38Bill is convinced that she and our other early human ancestors
01:07:44Flourished in a landscape that had been unintentionally prepared for them by elephants
01:07:50This idea of elephants opening things up and creating the conditions of success for early hominins
01:07:56This might not be an exaggeration to say that we might not be here without elephants
01:08:05And just like our ancestors, elephants did not stay put
01:08:10After millions of years in Africa, they started to leave
01:08:18Probosidians leave Africa multiple times
01:08:21Different groups leave at different times
01:08:24The first major foray out of Africa is around 18 million years
01:08:28And they make it all the way to Japan within a period of about a million years after getting out
01:08:33of Africa
01:08:45Until recently, all we knew of those ancient elephant species that left Africa
01:08:50was from a few fossil bones
01:08:54But then, a dramatically different kind of discovery brought them to life
01:09:04In the deserts of Abu Dhabi, scientists discovered not bones, but footprints
01:09:11They were made by ancient elephants
01:09:14A vivid record of their great migration out of Africa
01:09:19It's phenomenal because when you're actually on the landscape
01:09:22It seems like the elephants just passed there yesterday
01:09:25But we know geologically speaking that's impossible
01:09:27These are very, very old sediments
01:09:31So it was almost an afterthought to image the tracks from the air
01:09:37And then we went back to the hotel that night
01:09:39And we started to put the imagery together
01:09:43As we realized what we had, we basically, our jaws dropped
01:09:52What they saw was the footprints of an entire herd of ancient elephants on the move
01:09:59A snapshot in time of elephant behavior 7 million years ago
01:10:08Back then, this desert was a lush savannah
01:10:14The muddy ground after a rainfall captured their footprints perfectly
01:10:20All made by one of the strangest of elephant relatives
01:10:31It's probably ten minutes in the lives of these individuals, this herd that walked across the landscape
01:10:38And those ten minutes are forever preserved in these rocks for us to see
01:10:44And in that ten-minute snapshot
01:10:46Faisal can see all the dynamics of the herd
01:10:50The adults and calves
01:10:52A single bull male
01:10:54And a number of females
01:10:59Yeah, so we have, it's a minimum of 13 individuals actually
01:11:04You're walking along
01:11:05And here was a large individual
01:11:07There was probably the matriarch
01:11:11They slow down, they speed up a little
01:11:14There was a smaller guy
01:11:15He's on the edge, so
01:11:16We're clearly not too worried about any predators coming along on this landscape
01:11:22And then perhaps just the day before or the day after
01:11:26We've had the large bull
01:11:29Who also crossed this landscape
01:11:32Not long after Faisal and his team made their discovery
01:11:36They took Bill Sanders to see it
01:11:41I had no idea what awaited me
01:11:44And then I saw them
01:11:46All the footprints of an entire herd
01:11:48Going on for about 260 meters
01:11:52And you can see baby footprints
01:11:55Juvenile footprints, female footprints
01:11:59And then one great track of a big bull male
01:12:02That must have come along later and crossed that track
01:12:06And sort of checking out the herd
01:12:08We rarely get that opportunity
01:12:11I work on elephants
01:12:12I love elephants
01:12:14And I'm seeing their behavior crystallize in time
01:12:16All the way back to the very beginnings of elephants
01:12:19And I just started crying
01:12:22And my colleagues all sort of applauded
01:12:25And they realized I was not crying out of sadness
01:12:28I was crying because I was ecstatic
01:12:34Like skilled trackers, the scientists could read the ancient footprints
01:12:39And reconstruct a remarkably detailed picture of that day 7 million years ago
01:12:47We could estimate the actual size of these individuals based on stride lengths of modern elephants
01:12:53Where their weights are known and their stride lengths are known
01:12:55And their estimated weights go from a few hundred kilos for the small one
01:13:01Up to 5,000 kilos or so for the largest in the group
01:13:04And possibly 6,000 or so for the solitary individual that was walking at that site
01:13:09That makes them as big as any bull elephant today
01:13:15From fossils found nearby, we know that they were magnificent animals
01:13:20Four tusked beasts called Stegatetrabelodons
01:13:33And here you are, you're on this landscape and you can imagine them having just been here
01:13:37Like it was yesterday
01:13:40Over generations, their ancestors made the journey from Africa
01:13:45Thousands of miles away
01:13:49They're extinct, they're long gone
01:13:52And they haven't just left us their bones and teeth
01:13:55This is an imprint of their society
01:14:02The discoveries in Abu Dhabi show
01:14:04That by 7 million years ago
01:14:07The social behavior of elephants had already evolved
01:14:12Their close family bonds have been a key to the success of elephants for generations
01:14:20Even though Stegatetrabelodons disappeared a few million years ago
01:14:24Their descendants and other elephant species soon populated much of the globe
01:14:34Some, like the mammoths, adapted to the cold of Siberia and North America
01:14:40Others, like the Gomphithyrs, headed for the warmer climes of Southern Asia and Central America
01:14:49It had taken 60 million years
01:14:52But the elephant lineage had become one of the most successful on the planet
01:14:59Just 50,000 years ago, elephant species were on all continents except Australia, Antarctica and South America
01:15:11So what happened to them all?
01:15:16A long debate among my colleagues in my field has been
01:15:20What are the agencies for the extinction of the elephants that we see?
01:15:24For example, mammoths and mastodons
01:15:28One hypothesis is climate change
01:15:32At the end of the last ice age, 10,000 years ago
01:15:36The world warmed
01:15:40The cold adapted elephants of Siberia and North America
01:15:44Just couldn't deal with it
01:15:48In the northern hemisphere, in northern latitudes
01:15:51You have all this glaciation
01:15:53And these changes are happening very, very rapidly
01:15:57But for millions of years, the mammoths and mastodons managed to weather similar climate changes
01:16:05What was different about the warming at the end of the last ice age?
01:16:12Bill believes it was our own ancestors who tipped the balance
01:16:18So we see the great sites in Eurasia where indigenous peoples like 10,000 years ago
01:16:24And 50,000 years ago and 60,000 years ago were slaughtering these elephants in great numbers
01:16:30There is a tremendous predation pressure
01:16:33And imagine if you've got predation pressure hitting you on one side
01:16:37And now you've got this climate change
01:16:40And what it does to the landscape, what it does to the plants and the available resources
01:16:50By 4,000 years ago, the world was left with just the African, Asian and forest elephants we know today
01:16:59And now these are under threat as well
01:17:05This time, it has nothing to do with the end of an ice age
01:17:10Just us
01:17:16In 1800, there were an estimated 25 million elephants
01:17:23Today, there are less than a million
01:17:26And the number is falling fast
01:17:28Thanks to habitat loss
01:17:30And the relentless slaughter of elephants for ivory
01:17:40Poaching now is very mechanized, it's industrial
01:17:45In some places, we're losing 1,000 elephants in a month
01:17:49It's being done with not just weapons, but with aircraft
01:17:53Trains and trucks and ships
01:17:56To move the ivory out of Africa very quickly
01:18:01The tusks that helped elephants survive for millions of years have become a liability
01:18:07It's a new kind of evolutionary pressure
01:18:11Human-generated
01:18:13And in Africa, it's causing elephants to change almost overnight
01:18:20Over the millennia, elephants have evolved to have these huge tusks
01:18:24Because the most successful elephants are the ones that had the biggest tusks
01:18:28But over the last few hundred years, as human beings have been killing elephants for those tusks
01:18:34There are some populations of elephants who have very small tusks
01:18:36Because poachers are selectively removing elephants with big tusks
01:18:41And so the only females that get to breed are the ones that have very small tusks
01:18:45And so you increasingly see tusklessness in some of these elephant populations
01:18:50It would be such a tragedy if these magnificent animals lost the one thing that makes them, you know, so
01:19:00unique, their tasks
01:19:04Even as they adapt, elephants are at risk
01:19:09Like so many other creatures, they now face a new era of extinction
01:19:19Everywhere, the natural world is being transformed
01:19:34Our own lineage has become the planet's dominant evolutionary force
01:19:40Shaping the web of life that exists all around us
01:19:45This one recently arrived species is now the worldwide presence to which all others must adapt
01:19:54Our impact is so huge that our era has been given its own name
01:20:00The Anthropocene
01:20:02The Age of Humans
01:20:08It has seen the extinction rate among natural species soar to hundreds of times what it was before our arrival
01:20:19As scientists race to chart the planetary changes, they can look back at lessons from deep time
01:20:30They're observing many of the things that happened in earlier extinctions
01:20:36Rising CO2 levels leading to acidification of the oceans and rapid climate change
01:20:44Habitat destruction
01:20:50Many believe we are witnessing our planet's sixth mass extinction
01:20:57But the first one caused by a single species
01:21:01Like others, it will reset the evolutionary clock
01:21:05We just don't know how
01:21:10Today, when we live in a world where human populations are gradually changing the face of the globe
01:21:17By turning natural environments into artificial environments
01:21:21By pollution and many other ways of interfering with natural systems
01:21:26We are very much confronted with the question of evolution and extinction
01:21:30You can't have evolution without extinction
01:21:33But extinction really complicates our efforts to get the big picture
01:21:39We now know that mass extinctions are an engine of evolution
01:21:43Clearing out environments, making room for new species to evolve
01:21:48But in the past, they have usually taken millions of years
01:21:55This one is happening fast, in a matter of generations
01:22:02Viewed through the lens of deep time, that is a nanosecond
01:22:07Too fast for many living things to adapt
01:22:14But maybe not too fast for us to make a difference
01:22:21Crocs have lived on Earth for almost 230 million years
01:22:26They've survived cataclysmic extinction events
01:22:32But today, five of the 14 crocodile species are critically endangered
01:22:40Most of the living crocodilians were on the verge of extinction by the 1970s
01:22:46We were on the verge of losing all of them when we put in place protection
01:22:54Protections have helped
01:22:57In Australia, both fresh and saltwater crocs have rebounded
01:23:02Thanks to strong steps like restrictions on hunting
01:23:08But what about the other great survivors of deep history?
01:23:1410,000 species of birds still cover the globe
01:23:19Some have adapted to cities where they live beside us in seeming harmony
01:23:25But that's not the whole story
01:23:30We are hugely impacting bird evolution
01:23:34This is in habitat loss, consumption or killing
01:23:39Poisons, the use of toxins in our environment
01:23:45With 40% of bird species in decline
01:23:48There's reason to worry
01:23:50But also, reason to hope
01:23:55We managed to turn things around for iconic species like the bald eagle and California condor
01:24:03And innovative programs show that more is possible
01:24:08In 1974, only four Mauritius kestrels were left in the wild
01:24:15Today, there are a hundred times as many
01:24:18Thanks to predator control and captive breeding
01:24:27Ocean creatures need protection too
01:24:30It took 50 million years for whales to become
01:24:34The wondrous giants of the deep we know today
01:24:41But in just two centuries, industrial whaling brought many of them to the brink of extinction
01:24:49In the 20th century alone, almost 3 million whales were slaughtered
01:24:57It's unthinkable now that we exploited whales to the extent of, in the case of humpbacks, driving down their population
01:25:06to 10% of what they were globally
01:25:08They were almost pushed over the edge
01:25:11We only stopped whaling on northern Vancouver Island in 1967
01:25:17Humpbacks we stopped in 1965
01:25:20So, we thought of them so very differently
01:25:23We saw them as a resource
01:25:27But with humpbacks we have a second chance
01:25:32While some whales are critically endangered
01:25:36Whaling bands have made a difference
01:25:40Humpbacks have rebounded
01:25:43And blue whale populations, which fell to just 1500, seem to be slowly increasing
01:25:54One of the many things that the whales do
01:25:57One of the many things that the whales do
01:25:58Is they remind us how connected we are
01:26:01And of our capacity for change
01:26:07Around the planet, others are heeding that reminder
01:26:11Committing themselves to protect endangered animals and places
01:26:19In Kenya, Paula Kahumbu admires one of the last true giants left on earth
01:26:25A tusker named Tolstoy
01:26:32I feel very humbled to be able to meet Tolstoy
01:26:37He is a giant of giants
01:26:40He is not just a big tusker, he is a super tusker
01:26:43There are very, very few elephants
01:26:45Of that size with tusks of that length left in the world
01:26:50You know, when you are with Tolstoy
01:26:53One of the biggest rushes you get is that I am alive
01:26:56You just feel this sense of life
01:26:58It gives you goosebumps just to know that this elephant is aware of your presence
01:27:03And you are tiny and he is huge
01:27:04It is beautiful, it is just the most incredible experience
01:27:10To know that Tolstoy is the product of an evolutionary journey that has been going on for eons
01:27:16Only makes him more precious
01:27:20And Tolstoy is not alone
01:27:27Crocodiles and birds, whales and elephants are just four life forms among millions
01:27:34The tree of life is vast
01:27:37Encompassing everything that has ever lived
01:27:44What will its branches look like after the age of humans?
01:27:49The answer is up to us
01:27:52The moon is always about to me
01:27:53The moon is very beautiful
01:27:53The moon is already by the earth
01:27:53The moon is only by the moon is only the sun
01:27:53The moon is a huge way of the earth
01:27:56The moon is the west
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