{1149}{1297}For 40 million years the plains of|South America have been ruled by
{1277}{1361}an awesome group of predators
{1434}{1521}The aptly named terror birds.
{1797}{1884}But recently all this has changed.
{1933}{2064}A new breed of killer has arrived|one fierce enough to terrorise the
{2048}{2100}terror birds.
{2385}{2492}Smilodon, the f abled sabre tooth.
{2561}{2669}The most powerful big cat of all time.
{2996}{3100}There is no such thing as|a sabre tooth tiger.
{3088}{3189}The correct name for these beasts is|sabre tooth cats and there have
{3177}{3235}been many different species.
{3229}{3365}The largest, at over 300kgs,|is this one, Smilodon,
{3348}{3395}which means ''knife tooth''.
{3391}{3476}Originally from North America|they came to South America two
{3466}{3508}million years ago.
{3505}{3589}The balance of life here changed as|they took over the role
{3581}{3629}of top predators.
{3635}{3752}They live in tightly knit clans and|this is the story of three dramatic
{3737}{3859}months in the life of one particular|group led by a seven year old male
{3843}{3900}called Half Tooth.
{3929}{4002}Right from the beginning|Half Tooth has problems.
{3994}{4078}Recently a pair of|rival males have appeared.
{4179}{4257}And they want Half Tooth's crown.
{4565}{4658}Half Tooth's territory spans several|hundred square kilometres of
{4647}{4761}grassland on one of the strangest|continents on earth.
{4751}{4830}Since splitting from Antarctica|30 million years ago,
{4820}{4918}South America has been isolated from|the rest of the world and,
{4905}{4986}as a result, its animals are unique.
{4984}{5056}Oddities thrive here,|like Deodicurus,
{5049}{5176}a spiky-tailed relative of|the armadillo the size of a car.
{5196}{5277}Even the large herds of|herbivores are exotic.
{5267}{5374}These Macrauchenia are unrelated|to any modern mammal.
{5390}{5466}And then of course there are|the native predators,
{5457}{5531}the flightless terror birds.
{5536}{5653}These are three metres tall and|called Phorusrhacos.
{5659}{5759}But the isolation of these animals|came to an end when the movement
{5747}{5868}of the South American continent caused|it to collide with North America.
{5870}{5978}Across a land bridge came new groups|of mammals to colonise
{5965}{6011}this exotic world.
{6008}{6096}Life here would never be the same again.
{6161}{6222}Cats were among those colonists.
{6217}{6344}No cat had ever set foot in South|America before but now sabre
{6327}{6405}tooths ruled the grasslands.
{6433}{6522}Half Tooth took over this clan|three years ago,
{6512}{6584}breaking one sabre in the process.
{6583}{6660}The group is now made up of|four adult females and
{6651}{6705}their offspring.
{6718}{6799}All the youngsters are Half Tooth's.
{6870}{7014}During his reign, Half Tooth has seen|of many challenges from rival males.
{7052}{7139}But none as serious as this one.
{7132}{7245}Two rival males have wandered deep|into Half Tooth's territory.
{7235}{7320}As usual he is quick to respond.
{7349}{7461}But these are brothers and|they are working together.
{7509}{7608}Even by Smilodon standards|Half Tooth is a very large
{7595}{7726}male but he has never before f aced|two opponents at once.
{7709}{7793}The odds this time are|stacked against him.
{7988}{8076}The females read the signals and|start to retreat.
{8066}{8169}Their only concern is to|protect their offspring.
{8273}{8370}These fights can be brutal and|Half Tooth has the most to
{8359}{8496}lose - not only control of the clan|but possibly his life.
{9058}{9182}No match for the brothers,|Half Tooth is quick to back down.
{9230}{9339}He has at least escaped serious injury|but his problems are just
{9324}{9483}beginning. Life for a lone male is|a grim battle for survival.
{9664}{9780}Half Tooth hasn't had to feed himself|for three years because it was
{9765}{9850}the females in the clan|that did the hunting.
{9840}{9956}Outcast from the rich grasslands|now controlled by the brothers
{9941}{10052}he heads into the scrub forest|on the edges of his old territory
{10038}{10114}where he must learn|to scrape out a living.
{10146}{10248}With many of the creatures here|he stands no chance.
{10243}{10329}Doedicurus, for instance,|are not only well armoured,
{10319}{10367}they are huge.
{10367}{10447}These are ancient relatives of|the armadillo yet they weigh
{10438}{10518}almost 300 times as much.
{10648}{10765}Their spiked tail clubs alone|can weigh 40 kilos, as much as
{10751}{10797}a cannonball.
{10800}{10887}Although fearsome defensive weapons|the males mostly use their
{10877}{10923}tails on each other,
{10920}{11023}to batter rivals into submission|during hormone fuelled
{11010}{11060}jousts for a mate.
{11086}{11196}The loser ends up with more than|just his pride dented.
{11385}{11561}ln the clan, tensions are running high.|The females will not accept the
{11536}{11619}brothers while they still have young.
{11767}{11873}Defeating Half Tooth was only|part of the battle.
{11978}{12080}lf the brothers are to gain authority|over the clan they'll have to
{12068}{12117}kill the cubs.
{12267}{12354}Meanwhile, Half Tooth has pushed deeper|into the scrub forest
{12344}{12394}in search of food.
{12390}{12481}lf anything his task is g|etting more difficult.
{12479}{12633}The dense undergrowth harbours|another colossus, a sloth.
{12611}{12681}But this is no ordinary sloth.
{12716}{12839}This is Megatherium,|a giant ground sloth.
{12851}{12998}lt has huge claws, is six metres from|nose to tail and weighs more than
{12978}{13021}an elephant.
{13018}{13095}A very different beast from|its distant relatives,
{13087}{13148}the gentle tree sloths.
{13184}{13240}Half Tooth moves cautiously.
{13289}{13382}The sloth also boasts|impressive defences.
{13415}{13520}Small bones beneath his skin|act like chain mail.
{13506}{13601}Adults are virtually indestructible.
{13635}{13737}Half Tooth wisely gives|them a wide berth.
{14009}{14123}Weeks pass and the wet season|is in full swing.
{14189}{14281}The females have done their best|but only two of Half Tooth's
{14270}{14390}cubs survive and the brothers|are a constant danger.
{14459}{14563}They spend much of their time|patrolling their new territory,
{14551}{14683}spraying the boundaries with scent|as a warning to other males.
{14857}{14946}They will not attack the cubs while|the mother is present but
{14935}{15011}she must abandon them to go hunting.
{15008}{15112}This is when they are most at risk|and so this mother protects them
{15099}{15175}by hiding them in the dense undergrowth.
{15310}{15413}While the females are absent,|the brothers are spotted dangerously
{15401}{15472}close to the hiding place.
{15541}{15632}The cubs' lives hang by a thread.
{15647}{15747}Now their only hope is|to remain motionless.
{16281}{16393}Out on the plains there are large|herds of Macrauchenia.
{16378}{16514}Unique to South America, this species is|the last of their kind.
{16532}{16627}They are prime targets for Smilodon.
{16948}{17106}Macrauchenia are f ast, wary animals|and getting close enough to kill
{17083}{17143}one takes endless patience.
{17164}{17297}The females hunt together as a pack|inching forward to set the trap.
{17289}{17379}They have been closing in on this herd|for two hours now.
{17380}{17477}Gradually they f an out with the lead|female moving wide,
{17466}{17541}trying to encircle their pray.
{17563}{17689}Smilodon are powerful killers and|able to accelerate explosively
{17672}{17746}but they are not built for long chases
{17745}{17842}Unless they get close,|they don't stand a chance.
{18323}{18455}One f alse move and they will|have to start all over again.
{18921}{19028}The lead female drives the herd|towards the other females.
{19922}{20028}Having chosen their target,|the cats close in.
{20322}{20412}Macrauchenia have outstanding|manoeuvrability.
{20405}{20520}The victim jinks,|completely wrong-footing her pursuer.
{20547}{20632}But that's why Smilodon hunt in groups.
{20621}{20689}A second cat brings her down.
{21087}{21189}Surprisingly, as the cats fight to|restrain their prey,
{21177}{21305}they do not use their inf amous teeth|in case they break them.
{21388}{21492}First they work together to pin down|the struggling animal under
{21480}{21535}the weight of their bodies.
{21646}{21795}Only when the prey is totally subdued|are the f amous sabres drawn.
{21897}{22000}They are extraordinarily precise and|accurate tools for killing.
{21988}{22077}Their teeth simultaneously sever|the blood supply and strangle
{22068}{22111}the windpipe.
{22108}{22174}One bite and the prey is dead.
{22173}{22246}But these are the original|double-edged swords.
{22238}{22382}The lethal 20cm sabres are|actually quite fragile.
{22370}{22465}They cannot bite into bone and|so Smilodon can only eat
{22454}{22516}the fleshier parts of a carcass.
{22510}{22554}This is very wasteful.
{22551}{22678}Something that hasn't gone unnoticed by|other carnivores on the grasslands.
{22882}{22970}The terror birds are|supreme opportunists.
{22961}{23041}They may have been replaced as|top predators but they have
{23032}{23149}quickly found new ways of surviving,|thanks to the cats.
{23509}{23601}Eventually the Smilodon have eaten|as much as their sabres
{23590}{23622}will allow them.
{23621}{23713}They live the kill for|the birds to pick over.
{23755}{23861}South America is not the only place|terror birds are doing well.
{23847}{23929}Once the land bridge opened to|North America they were
{23921}{24008}one of the few creatures|to spread north successfully.
{23998}{24082}While these terror birds eat Smilodon's|leftovers,
{24073}{24171}their cousins are running riot|in Texas and Florida.
{24256}{24368}They only died out just before|modern humans appeared.
{24510}{24614}After the hunt, the mother returns|to where she hid the cubs
{24601}{24690}as she has done several|times over the last weeks.
{24766}{24904}She calls to them but|her calls go unanswered.
{25255}{25369}Half Tooth is soon spotted nearby|roaming on the fringes of
{25355}{25428}a territory|that used to be his own.
{25521}{25625}But where he once sprayed,|he can clearly smell the scent
{25613}{25662}of the brothers.
{25739}{25830}That is not the only signal|they have left.
{26099}{26188}With the death of his cubs|his last tie with the group
{26177}{26225}has been severed.
{26222}{26302}The take-over is complete.
{26663}{26777}Sighting of Half Tooth have started|to become rare and it is clear
{26763}{26877}from his physical condition|he is not thriving in the scrub forest.
{26887}{26991}lt is dawn and Half Tooth is exploiting|his sensitive vision to hunt
{26979}{27023}in the low light.
{27090}{27203}Male Macrauchenia live separately from|the herds and often wander into
{27189}{27251}the scrub forest to browse,
{27246}{27330}using their long noses to|strip fresh leaves.
{27518}{27604}Half Tooth waits and allows|the Macrauchenia to wander
{27594}{27655}ever closer.
{27649}{27725}There must be no mistakes this time.
{27920}{28022}But a giant ground sloth is about|to ruin everything.
{28010}{28108}As he crashes through the undergrowth,|Half Tooth's quarry starts
{28096}{28142}moving away.
{28176}{28232}lt's now or never
{28547}{28627}Half Tooth is too weak to follow.
{28629}{28760}The longer he goes without a kill|the smaller his chance
{28742}{28779}of making one.
{29006}{29101}lncreasingly desperate,|he is seen still patrolling
{29089}{29150}the same area later that morning.
{29355}{29485}He spots a Macrauchenia mother and|young close to the forest edge.
{29470}{29554}They have wandered away from|the main herd.
{29550}{29609}Maybe this time.
{30022}{30111}With a lightening strike of|its massive beak and claws,
{30101}{30203}a terror bird comes|from nowhere to kill the youngster.
{30380}{30541}But all is not lost for Half Tooth.|He seizes his chance.
{30892}{30978}Scavenging is now his best hope.
{30978}{31135}But after finishing this skill Half|Tooth disappeared from this scrub forest
{31362}{31495}Not f ar away, the brothers have|completely usurped Half Tooth.
{31484}{31607}With the last of the cubs dead|the clan has now accepted them
{31718}{31809}The remaining adolescents are tolerated|by the brothers because
{31797}{31914}they are female and will soon|be old enough to mate.
{31943}{32079}And with no cubs to suckle,|the older females come into heat again.
{32061}{32172}Killing Half Tooth's cubs was not|just a pointless act of violence.
{32159}{32264}With the cubs out of the way the clan|can now concentrate on raising
{32251}{32391}the brothers' offspring and passing|their genes onto the next generation.
{32588}{32683}All in all, the clan is|returning to normal.
{32692}{32796}The young females practice|their hunting skills.
{32866}{32955}Although the Deodicurus|they have picked on has little time
{32945}{32985}for their games.
{33311}{33409}The rainy season has come and gone|and Half Tooth has not been
{33398}{33450}seen for weeks.
{33446}{33533}His old clan, however|is very much in evidence.
{33526}{33626}They have been making a kill every|few days and today they're once
{33614}{33680}again feeding well.
{33752}{33858}As usual, the terror birds|are not f ar away.
{33856}{33998}But on this occasion there is|another scavenger, a Megatherium.
{33982}{34044}They might be herbivores but they will|occasionally go for carrion to
{34038}{34141}supplement their diet.
{34133}{34230}And when they do,|nothing gets in their way.
{34602}{34659}One of the brothers has been killed.
{34655}{34767}The rest of the Smilodon quickly|abandon the kill to the giant.
{34883}{34983}ln the blink of an eye the Megatherium|has changed everything for
{34972}{35011}the clan.
{35032}{35114}Now there's only one brother left.
{35320}{35431}Within days Half Tooth|suddenly reappears.
{35420}{35518}He must have been closely monitoring|his old territory.
{35515}{35631}And so sensitive is the sense of|smell in cats that he can tell
{35616}{35728}the identity and even the health|of a male who has left his scent.
{35717}{35818}ln this case the marks are easy to|interpret - where there were once
{35806}{35912}two males, now there is only one.
{36124}{36244}Within the clan, things are going|badly for the remaining male.
{36246}{36354}He was not the dominant of the|two brothers and the females appear
{36340}{36411}to have become unsettled again.
{36604}{36712}But it is not the females that|the lone brother is worried about.
{36703}{36839}lt is only a matter of time before|other males come looking for trouble.
{37129}{37259}He continues to patrol his territory|but a challenge will come sooner
{37241}{37309}than the brother expects.
{37408}{37507}Half Tooth is back|Encouraged by the signals,
{37496}{37625}he is wasting no time in|trying to reclaim the clan.
{37673}{37758}A fresh scent trail leads him on.
{38307}{38369}Three months after losing|to the brothers,
{38363}{38488}Half Tooth is once again about|to fight for this territory.
{38698}{38773}The odds this time have evened up.
{39566}{39689}The fight is brief and brutal|but Half Tooth triumphs.
{39892}{40037}The brother is defeated|and f atally injured.
{40150}{40277}Unlike Half Tooth|this cat will get no second chance.
{40422}{40542}The short, violent reign of|the brothers is over.
{40983}{41125}A year later finds Half Tooth surrounded|by new arrivals of his own.
{41119}{41209}He is king of the grasslands again.
{41312}{41426}Smilodon were very successful predators|and survived up until as
{41410}{41498}recently as 10,000 years ago.
{41521}{41620}But eventually the world around|them changed too much.
{41606}{41726}The climate became cooler and drier|the larger prey they specialised
{41711}{41766}in killing disappeared.
{41769}{41879}The sabre tooth world came to an end.
{42053}{42119}ln our final episode things|will get much
{42113}{42275}much colder as we visit our ancestors|in an ice age 30,000 years ago.
{42280}{42387}lt was the toughest of times and|gave rise to one of the most
{42374}{42556}awesome mammals of all|- the mammoths.