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Documentary, PaleoWorld PaeoWord S01E08 - Attack Of The Killer Kangaroos
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AnimalsTranscript
00:03Koalas, kangaroos, curious creatures who carry their young in pouches.
00:09Scientists once thought such animals were dropouts in the evolutionary race
00:14and could only survive in the isolation of Australia.
00:18But recent discoveries tell a different story.
00:22Bloodthirsty, saber-toothed marsupials made a stand on every continent of the world.
00:29Millions of years ago came the attack of the killer kangaroos.
01:11Australia has been called the world's great evolutionary laboratory.
01:21Isolated from the rest of the continents for millions of years,
01:25its native animals have been, biologically speaking, free to travel the road less taken.
01:31These extraordinary creatures are the living symbols of Australia.
01:36Teddy bear-like koalas, bounding big-eared kangaroos, slow, docile wombats, and cartoon-inspiring Tasmanian devils.
01:54Australia's marsupials have always struck outsiders as quaint, cuddly, and sometimes comical.
02:09But the fossil record in Australia is introducing paleontologists to an array of marsupials more diverse and unique
02:18than anyone would have imagined.
02:23Australia is a tough land for the paleontologists.
02:26It lacks the kind of geological forces that wrench up mountains and tear gashes into ancient fossil-laden sediments.
02:34For most of this century, the fossil record before 50 million years ago was a virtual blank.
02:41Discovered in 1983, the fossil site known as Riversley in western Queensland would change all that.
02:48This unglamorous sheep station would soon produce enough fossils to quadruple Australia's entire paleontological record.
02:56For a decade, paleontologist Michael Archer and his colleagues have been reaping a rich scientific harvest from Riversley.
03:04After digging up the limestone sediments, they hauled them back to the lab at the University of New South Wales.
03:12A good soaking in acid often rewards the paleontologists with a chaotic jumble of ancient jaws, teeth, and other bones
03:22of long-gone marsupials.
03:25Archer has discovered that many living marsupials have rather fearsome skeletons in the closet.
03:31Here's an assortment of the sorts of things they were finding in Riversley about 20 million years ago.
03:36It includes all sorts of strange herbivores, carnivores.
03:40One of the ones that just blew our mind right in the beginning was a thing that ought to be
03:45a representative of one of the gentlest, you know, cutest sort of groups, a kangaroo.
03:50This thing, this offence to the senses, was a flesh-eating kangaroo.
03:56Armed with rapier teeth and voracious appetites, the bloodthirsty kangaroos that stalked the plains of Australia millions of years ago
04:05are just part of the remarkable evolutionary tale of the marsupials.
04:12Today, there are three classes of mammals in the world.
04:17Placental mammals, marsupials, and monotremes.
04:25They differ primarily in how they reproduce.
04:29Monotremes lay eggs.
04:31Only two types of these strange mammals survive.
04:35The spiny anteater and the duck-willed platypus.
04:41They're found in the wild only in Australia and New Guinea.
04:47Placental mammals like us, and like this pregnant hyena, carry a developing fetus in the womb.
04:58Eleven days after conception, a baby opossum enters the world, hairless, underdeveloped, and functionally blind.
05:10Within minutes, it will crawl up to its mother's pouch, perhaps the most perilous journey of its life.
05:21There, it will spend the next nine to ten months feeding and growing into a fully developed infant.
05:33Remarkable though this birthing process is, biologists have always assumed that the placental way of reproducing is the superior one.
05:41The argument has been that because placental babies spend a long time in the womb, they are born better developed.
05:52Regardless of the zoological debate, the distribution of mammals in the world today is quite lopsided.
06:00Placental mammals dominate everywhere but Australia and New Zealand, all of the continents, and the seas as well.
06:11Australia and New Zealand, on the other hand, belong to the marsupials.
06:22Aside from a handful of newcomers, Australia has a remarkable lack of placental mammals.
06:32But it wasn't always so.
06:36Marsupial fossils have been found on just about every continent in the world.
06:42Why did the marsupials thrive in Australia and die out just about everywhere else?
06:50Scientists have long held that on the continents where marsupials competed head to head with placentals, the placentals won out.
06:58On the island continent, where there were no placentals, the marsupials were granted a reprise.
07:05In fact, the usual idea, it goes back to Matthew, a chap in the United States, is that marsupials came
07:11here because they were forced out of the northern lands as inferior mammals
07:15and forced into the corners of the world that the placentals didn't want.
07:19The notion that marsupials are somehow inferior is deeply rooted in traditional biology.
07:26Zoology texts commonly refer to them as primitive.
07:29Even their technical names reveal a bit of placental condescension, according to zoologist Bruce Brewer.
07:36The marsupials are members of the metatheria, which means animals that are almost good beasts.
07:42And then we, the placental mammals, since we made up this terminology, are the eutheria, or the good beast.
07:49The biologists have had this preconception that because we are placental mammals, that is, we don't have our young in
07:56a pouch or anything,
07:57that must be the superior type of mammal, and that anything else is somehow an inferior approximation to this placental
08:02condition.
08:03If so, how did marsupials manage to reach the safe haven of Australia and survive?
08:10According to traditional dogma, they were saved by continental drift during the Eocene, 50 million years ago.
08:18They were lucky refugees from an ancient time when all the continents were connected.
08:24They assumed that that was because when Australia broke away from Gondwana about 45 million years ago,
08:31only marsupials had managed to get here.
08:33But new fossil discoveries from Riversley are rewriting the natural history of the mammals.
08:38A startling find hints that the marsupials may not have fled from their placental cousins, but instead conquered Australia.
08:52No one knows exactly where or when the evolutionary rivalry between the marsupial mammals and the placental mammals began,
08:59but it stretches back at least 100 million years.
09:04The earliest marsupial fossils discovered point to the northern hemisphere,
09:09not Australia as the cradle of marsupial evolution.
09:15This stretch of badlands in central Utah is Robber's Roost,
09:20where the infamous Butch Cassidy often hid from the law.
09:31paleontologists have long hunted other renegades here, the great dinosaurs.
09:41But University of Oklahoma paleontologist Richard Cefeli has come here in search of much smaller game,
09:49some no bigger than the head of a pin.
09:57Do you think it rained crocodiles here or something?
10:04It's a needle in a haystack business and back-breaking work.
10:10Cefeli and his team haul gunny sacks full of sediment back to camp,
10:16where their work looks more like prospecting for gold than digging up fossils.
10:24They must first soak the hard rock deposits in water,
10:27sifting out the tiny fossils and drying them in the hot desert sun.
10:33The casual observer might think they were sluicing for the glint of precious metals or gems.
10:39But their painstaking work does produce gems of a sort.
10:43It was here, in 1992, that Cefeli found the world's oldest known marsupial.
10:52Here in my left hand is the lower jaw of this thing we're calling cocopelia.
10:58It's a marsupial or proto-marsupial.
11:00Maybe a mouse-sized animal.
11:03Probably would have looked like a Virginia opossum shrunk way down to mouse size.
11:07This animal is about a hundred million years old, so it was living during the age of dinosaurs
11:14and living in the footsteps of giants, literally.
11:18There were a lot of pretty fierce predators around at that tunnel,
11:22so not a good place to be if you're a furry little creature.
11:27For another 35 million years, the world would remain a dangerous place for the little mammals living underfoot of the
11:34dinosaur.
11:35But then the dinosaurs died out.
11:38Mammals had free reign of the planet, and they took it.
11:42The starting gun sounded for the race between the pouched mammals and the unpouched mammals.
11:48Their fates would be dictated by their distinctive strategies for reproducing,
11:54and the deck seemed stacked against the marsupials.
11:58Marsupials are primitive in that they are forced to give birth very soon after conception,
12:05within a matter of a couple weeks, say.
12:09This is because the young is not genetically identical with the mom,
12:13and so as it develops, the mom's immune system recognizes it as an alien and has to get rid of
12:19it.
12:20So birth takes place very quickly.
12:23Placentals have invented this fancy system of embryonic membranes
12:29that pretty much insulates junior from mom and allows prolonged intrauterine development.
12:38And that's critical to the success of placental mammals.
12:43Most importantly, the brain can grow larger in a womb than in a pouch,
12:49giving placentals an edge in intelligence and allowing them to create more sophisticated social systems.
12:57Placentals were able to specialize physiologically as well,
13:01which allowed them to diversify and fill varied ecological niches.
13:07Marsupials never were able to specialize into things that placentals did in terms of having really strongly modified forelimbs,
13:17flippers for instance, or flying-type wings like bats have.
13:22If you're going to modify those forelimbs, you have to start very early in development.
13:26Marsupials can't do that because they're forced to have these forelimbs developed in a certain way,
13:31so they can climb and get into the pouch.
13:36Despite what may seem like handicaps, the marsupials clearly had the upper hand in the southern parts of the world.
13:44Marsupials really took off on the continents of Australia and South America,
13:49and we find all these tremendous examples of convergent evolution.
13:53That is, marsupials doing the same things that placentals were doing on other continents.
13:59For example, in South America, there was a marsupial saber-tooth,
14:04look for all the world, like a placental saber-tooth.
14:07And this is a large lion-sized animal with canine teeth,
14:12the fangs that could have been six or seven inches long.
14:15Clearly a major predator there.
14:19There were gigantic grizzly bear-sized boar hyenoids that probably were partly carnivorous to omnivorous,
14:27basically eat whatever they wanted to.
14:33The marsupial killers stayed top dog in South America for some 60 million years.
14:39But by two million years ago, the big predatory marsupials of South America had all but disappeared,
14:47outcompeted by the likes of the new placental saber-toothed cats and great bears.
14:53These newcomers traveled to South America across a newly formed land bridge now connecting the continents.
15:00For many decades, biologists saw a clear implication in this succession.
15:05The superior placentals had driven the inferior marsupials to extinction.
15:11It was justifiable fratricide in the best Darwinian tradition.
15:17But now, a new, more ominous creature was about to appear on the scene
15:23and overturned decades of scientific belief.
15:30At Riversley, the fossils are revealing a marsupial past that belies their gentle image.
15:38Michael Archer has pieced together a portrait of a vicious predator reborn from Australia's past.
15:47Standing about five feet tall and burlier than today's kangaroos,
15:52these sharp-toothed killers probably snacked on their more docile relatives.
15:57The modern kangaroo is not the only living marsupial with a skeleton in the closet.
16:03The sluggish vegetarian wombat has its own bloodthirsty ancient cousin.
16:11Among the other sorts of spectacular types of fleshy animals that developed in Australia, marsupials,
16:17were these marsupial lions, aptly named pouched animals that were, at their larger size,
16:24the size of a fully grown adult lion.
16:26Incredible things.
16:27And studies of the teeth of these animals have demonstrated that they are more specialized as carnivores
16:33than any other mammal has ever been anywhere at any time in the world.
16:37They had, much like the carnivorous kangaroos did,
16:41they probably used their very powerful lower incisors as stabbing devices.
16:45Again, these are monstrous stilettos for tearing, perhaps ripping open the prey.
16:52They had a whole range of smorgasbord of things to eat at this time.
16:55This was in the end of the Pleistocene.
16:56They were giant kangaroos, three meters or about nine feet tall.
17:00They were giant wombats the size of a small horse.
17:03There was a whole range of things, hippopotamus-sized marsupials, all of them yummy.
17:10These marsupial lions roamed the Australian plains until just 30,000 years ago.
17:19By then, the aboriginal people had already arrived,
17:22and almost certainly had some unfortunate encounters with the big pouched lions.
17:32And I'm certain that would have been one of the most unpleasant sights any human being ever saw
17:37as they went into the great hunting ground was to see one of these things coming up on them.
17:42To see an animal with bolt-cutting teeth the size of these things
17:47that could cut a leg off a kangaroo without even sort of batting an eye.
17:52The teeth when they come together are just like the kind of giant bolt cutters
17:56that you might find in any hardware store today.
17:59So it would have made camping in those days an extremely interesting experience.
18:04But the discovery that has rocked the scientific community
18:09is this tiny fossil tooth of a placental mammal
18:13which Archer found in 55-million-year-old Australian sediment.
18:19In that clay we found, sure, what we expected, marsupials galore, all sorts of interesting things,
18:25but lo and behold, a placental mammal.
18:29Most scientists assume marsupials arrived in Australia before placental mammals.
18:35When the island continent split off, the marsupials were left alone to evolve without competition.
18:42In effect, they won Australia by default.
18:45But the tooth would change Archer's mind.
18:48The only parsimonious conclusion had to be it was a placental mammal that was here with the marsupials in Australia
18:56at the same time.
18:57They started in the racing blocks at the same time.
19:00When the gun went off, those placentals fell on their face.
19:03The marsupials basically picked them up with a great smile on their face and kicked them off the edge of
19:07the continent.
19:14Archer sent casts of the tooth to experts around the world, comparing the number and position of the cusps.
19:21Most of them came to the same stunned conclusion.
19:25It looked more like a placental molar than a marsupial one.
19:30When Archer and Goodhelp published the results, scientists were quick to understand the enormous implications.
19:40Marsupials didn't win by default.
19:42They had the advantage.
19:46The important thing about that tooth, if it is a placental, is that it shows placentals were present in Australia
19:51early on,
19:53and that they didn't out-compete marsupials.
19:56In fact, quite the contrary, that marsupials took over in the presence of placentals.
20:01So that contradicts sort of a long-standing scenario.
20:07Clearly, Archer's discovery of a placental tooth at Riversley is compelling.
20:13But many scientists are not yet willing to rewrite the natural history of Australia
20:18on the strength of something so small and so singular.
20:23Australian paleontologist Tim Flannery is not so easily convinced.
20:28The idea that there's been primitive placental animals in Australia really is based on one tooth.
20:34It's only about two millimetres long, but even worse, it's based on the position of one cusp on one tooth,
20:39which is only a relative thing, you know, very, very small differences.
20:42There's a lot of difficulty in identifying a single isolated tooth.
20:47Like I said, I think a defensible argument has been made that it is placental.
20:52It does compare very closely also to some marsupial groups, and so I think the jury's still out on that
20:59one.
21:01Whether marsupials outcompeted placentals or won by default is still open to debate.
21:07But one thing is certain.
21:10Marsupials were designed for Australia's unique environment.
21:15Well, Australia's always been the most different of all of the continents.
21:18It's been isolated for a very long time from all of the others.
21:21And it's also had very strange conditions here.
21:24For instance, Australian soils are terribly infertile, what we've got of them.
21:27A lot of the countries just rock.
21:29And we've also got this really strange climatic pattern, which is called the Southern Oscillation.
21:33And that means that rainfall in Australia isn't regular.
21:36As some of our early poets said, it's a land of drought and flooding rain.
21:39There's not much in between. There's not really an average year.
21:41And those conditions make life really hard for animals like mammals.
21:45So it's always been odd, an odd continent.
21:47And maybe that explains in part why the marsupials have done so well here.
21:52Marsupials don't use as much energy as placentals, just because when they're sitting around doing nothing,
21:55their metabolic rate is a lot lower than placental mammals.
21:58So that gives them a bit of an advantage.
22:02The rough climate of Australia becomes advantageous to marsupials because of their unique reproductive system.
22:12For marsupials, the young is in the pouch. There's very little investment.
22:15If times are bad, if there's a drought, something like that, you can eject the young and cut your losses,
22:22essentially, and live to reproduce again.
22:27Perhaps Riversley will yield up more secrets of the marsupial saga in Australia.
22:32But for now, the scientific community is looking at marsupials with new respect.
22:42In many ways, it would seem that such an indication for marsupials is a hollow victory.
22:48The age of the great carnivorous marsupials is over.
22:53The marsupial lions were gone by 30,000 years ago.
22:57The marsupial wolf, also called the Tasmanian tiger, was in serious decline by the modern age.
23:05European settlers saw it as a pest and hastened its demise with a single-minded determination.
23:15In 1936, the last known Tasmanian wolf died in captivity.
23:24Today, the small but fierce Tasmanian devil is on the endangered list.
23:32But an unlikely champion of the marsupial cause has made a stand in the northern hemisphere.
23:40The unassuming opossum has increased its range from South America all the way up to Canada.
23:51And even the common kangaroo is making unexpected inroads into the north.
23:55Released into some of the dwindling wilds of England and Germany,
24:00kangaroos seem to be thriving.
24:03It is Australia, land down under, with its rugged inhospitable terrain,
24:09that will always be the domain of the marsupials
24:12and the ancient home of the killer kangaroos.
24:16Oursuos.
24:20Oursuos!
24:41Oursuos
24:42G plays
24:45Osuos
25:13Transcription by CastingWords
25:17CastingWords
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