1 00:01:02,687 --> 00:01:07,636 This is one of the coldest places on Earth - the high Arctic. 2 00:01:07,807 --> 00:01:12,562 The temperature drops to 50 degrees below freezing. 3 00:01:12,727 --> 00:01:18,085 Without this specialist clothing, the cold would kill me in minutes. 4 00:01:18,247 --> 00:01:22,001 Yet there are animals that live here all the time. 5 00:01:22,167 --> 00:01:26,763 One of the most remarkable is hunting over there... 6 00:01:30,447 --> 00:01:33,007 an Arctic fox. 7 00:01:33,167 --> 00:01:36,876 The only reason it and I don't freeze solid 8 00:01:37,047 --> 00:01:40,926 is that we are mammals and have the mammal's ability 9 00:01:41,087 --> 00:01:44,557 to use food to heat our bodies. We are warm-blooded. 10 00:01:44,727 --> 00:01:48,845 The reason it is more at home up here than I am 11 00:01:49,007 --> 00:01:54,525 is that it has more of that other mammalian characteristic, hair, than I have. 12 00:01:54,687 --> 00:01:58,043 Its body is insulated with fur. 13 00:01:58,287 --> 00:02:01,677 Warm-bloodedness is one of the key factors 14 00:02:01,847 --> 00:02:04,520 that enabled mammals to conquer the earth 15 00:02:04,687 --> 00:02:09,681 and to develop the most complex bodies in the animal kingdom. 16 00:02:16,967 --> 00:02:19,083 In this series, we will travel the world 17 00:02:19,247 --> 00:02:24,162 to discover how varied and astonishing mammals are. 18 00:02:27,727 --> 00:02:31,720 We go to Africa, where mammals are at their most spectacular. 19 00:02:31,887 --> 00:02:36,119 The plains are thronged with specialist grass-eaters. 20 00:02:37,847 --> 00:02:42,398 There are other mammals here too, with different tastes. 21 00:02:47,847 --> 00:02:52,284 Some hunting mammals have become the fastest creatures on Earth. 22 00:02:53,407 --> 00:02:57,685 Those they hunt have had to respond or die. 23 00:03:03,047 --> 00:03:07,040 Some mammals have become fearsomely strong and aggressive. 24 00:03:12,687 --> 00:03:14,882 They fight for mates. 25 00:03:21,647 --> 00:03:24,161 They fight for food. 26 00:03:27,047 --> 00:03:30,483 Some even have to fight for a place to live. 27 00:03:30,967 --> 00:03:36,917 Wherever you go, you find a bewildering variety of mammals. 28 00:03:39,967 --> 00:03:42,925 Some are miniatures, a few inches long. 29 00:03:44,407 --> 00:03:47,126 Others are massive. 30 00:03:52,687 --> 00:03:56,965 The biggest of those on land are dwarfed by those in the sea. 31 00:03:57,127 --> 00:04:01,405 I can see its tail, just under my boat here. 32 00:04:01,567 --> 00:04:04,286 It's coming up! 33 00:04:04,447 --> 00:04:08,440 There! The blue whale! 34 00:04:08,607 --> 00:04:14,204 It's the biggest creature that exists, or has ever existed, on the planet. 35 00:04:22,887 --> 00:04:27,756 Mammals are as at home in the water as they are on land. 36 00:04:28,487 --> 00:04:31,877 Some lounge around on the surface. 37 00:04:33,807 --> 00:04:36,640 Others prefer to do so on the beach. 38 00:04:38,847 --> 00:04:41,964 We will go underground to track them. 39 00:04:42,687 --> 00:04:46,316 And up into the tops of the tallest trees. 40 00:05:09,487 --> 00:05:15,164 Mammals have even taken to the air and challenged the birds. 41 00:05:16,767 --> 00:05:20,316 They can congregate in astronomical numbers. 42 00:05:21,167 --> 00:05:23,806 They thrive almost everywhere. 43 00:05:24,447 --> 00:05:26,677 Precisely how they do so depends, 44 00:05:26,847 --> 00:05:30,635 as in so much in life, on what they eat. 45 00:05:32,527 --> 00:05:35,963 Between them, they tackle everything that's edible. 46 00:05:45,247 --> 00:05:48,876 Some are very particular about their food. 47 00:05:49,047 --> 00:05:54,167 Others will take the best of what is around at the time. 48 00:05:54,567 --> 00:05:59,118 Top of the menu right now is...salmon. 49 00:06:03,607 --> 00:06:07,680 We will look at the lives of our closest relatives. 50 00:06:07,847 --> 00:06:09,883 (HE CHORTLES) 51 00:06:14,047 --> 00:06:17,198 And they will lead us to ourselves - 52 00:06:18,447 --> 00:06:24,716 perhaps the most successful variation of the mammal's winning design. 53 00:06:35,727 --> 00:06:40,323 To glimpse the beginnings of the mammalian dynasty, 54 00:06:40,487 --> 00:06:43,001 we must travel to Australia. 55 00:06:45,567 --> 00:06:49,037 (CLICK OF RECEIVER) 56 00:06:52,767 --> 00:06:57,682 I'm looking for one of the most ancient of all mammals. 57 00:06:57,847 --> 00:07:02,716 So ancient, it shares at least one characteristic with reptiles. 58 00:07:03,647 --> 00:07:07,959 It's a very elusive creature, but here in South Australia, 59 00:07:08,127 --> 00:07:12,439 there's a population that's been fitted with radio transmitters 60 00:07:12,607 --> 00:07:15,326 and I can track them with this aerial. 61 00:07:15,487 --> 00:07:18,604 I've got a very strong signal. 62 00:07:28,807 --> 00:07:33,005 At first glance you might think this is a sort of hedgehog... 63 00:07:36,167 --> 00:07:38,158 or a porcupine. 64 00:07:38,327 --> 00:07:42,605 But it's weirdly different from a hedgehog, porcupine 65 00:07:42,767 --> 00:07:45,281 or any other kind of mammal. 66 00:07:49,807 --> 00:07:52,526 (WHISPERS) It's an echidna. 67 00:07:52,687 --> 00:07:57,966 You can tell it's a mammal because it's got hair. 68 00:07:58,047 --> 00:08:00,800 Only mammals have hair. 69 00:08:00,967 --> 00:08:05,995 Some of its hairs have been enlarged and strengthened 70 00:08:06,167 --> 00:08:12,117 and have turned into big spines, giving it an effective armour. 71 00:08:13,927 --> 00:08:17,556 This hair keeps the echidna warm, 72 00:08:17,727 --> 00:08:23,882 ensuring it doesn't lose valuable body heat to the cold air. 73 00:08:34,527 --> 00:08:39,442 The fuel with which it and all mammals generates that heat is food. 74 00:08:39,607 --> 00:08:43,964 On a cold winter's day like this, it has to spend its time 75 00:08:44,127 --> 00:08:48,166 searching for its next meal to make sure it's fully stoked up. 76 00:08:48,327 --> 00:08:52,081 Although echidnas have good eyesight and excellent hearing, 77 00:08:52,247 --> 00:08:55,444 it's their sense of smell which guides them to food. 78 00:08:56,287 --> 00:08:58,721 They sniff out insects and grubs, 79 00:08:58,887 --> 00:09:02,038 then get at them by ripping open the nests and tunnels 80 00:09:02,207 --> 00:09:04,926 with their immensely strong claws. 81 00:09:09,647 --> 00:09:13,196 That beak-like snout pokes into holes, 82 00:09:13,367 --> 00:09:16,245 then out comes a long sticky tongue, 83 00:09:16,407 --> 00:09:20,764 that flicks into crevices to lick up whatever's worth eating. 84 00:09:27,807 --> 00:09:31,402 Echidnas are particularly fond of ants and termites, 85 00:09:31,567 --> 00:09:34,400 and will even climb trees to find them. 86 00:09:46,767 --> 00:09:51,443 This particular female has an unusually healthy appetite 87 00:09:51,607 --> 00:09:53,598 because she's about to breed. 88 00:09:53,767 --> 00:09:59,285 And the way she does so is why the echidna is such a weird mammal. 89 00:10:04,727 --> 00:10:09,926 The echidna doesn't give birth to live babies, she lays an egg. 90 00:10:10,087 --> 00:10:14,638 It's hidden in her fur in a shallow depression on her underside. 91 00:10:14,807 --> 00:10:17,082 It's no bigger than a marble. 92 00:10:17,807 --> 00:10:21,561 Inside it, a young echidna is developing. 93 00:10:25,087 --> 00:10:29,046 After hatching, she carries it around on her underside 94 00:10:29,207 --> 00:10:33,359 for about 50 days, until it develops spines. 95 00:10:33,527 --> 00:10:39,682 She then deposits it in a burrow, where it stays and grows for nearly seven months. 96 00:10:39,847 --> 00:10:42,919 But how does she feed it during this long time? 97 00:10:46,407 --> 00:10:51,356 For the answer, we must find the only other egg-laying mammal. 98 00:10:51,527 --> 00:10:53,165 It too lives in Australia. 99 00:11:14,367 --> 00:11:16,961 Surfacing beside me here 100 00:11:17,127 --> 00:11:20,563 is one of the most extraordinary animals in the world. 101 00:11:27,207 --> 00:11:31,086 It's so bizarre that when specimens of it 102 00:11:31,247 --> 00:11:33,966 were first sent from here to Europe, 103 00:11:34,127 --> 00:11:37,437 people thought it must be a fake. 104 00:11:37,607 --> 00:11:44,240 But it's not. It's real, it's alive, it's a platypus. 105 00:11:48,887 --> 00:11:52,562 That bill looks as though it should belong to a duck. 106 00:11:52,727 --> 00:11:56,561 But it's not hard like a bird's beak, it's rubbery. 107 00:12:02,687 --> 00:12:07,044 Like the echidna, the platypus feeds on small invertebrates, 108 00:12:07,207 --> 00:12:10,040 but it looks for them under water. 109 00:12:13,567 --> 00:12:16,127 Once it has collected a mouthful, 110 00:12:16,287 --> 00:12:19,120 it takes them to the surface and grinds them to a pulp. 111 00:12:19,287 --> 00:12:24,156 It has no teeth. Horny plates in the bill do the job. 112 00:12:27,407 --> 00:12:29,602 How does it find that food? 113 00:12:30,727 --> 00:12:36,723 Underwater, it closes its eyelids tight so it can't see anything. 114 00:12:38,967 --> 00:12:43,358 It has a remote sensing device, its bill. 115 00:12:43,527 --> 00:12:46,724 As it sweeps it from side to side like a metal detector, 116 00:12:46,887 --> 00:12:51,244 sensors in it pick up infinitesimally tiny currents 117 00:12:51,407 --> 00:12:54,444 given off by all living things. 118 00:13:02,207 --> 00:13:06,200 There were few mammals on Earth 100 million years ago 119 00:13:06,367 --> 00:13:08,198 when the first platypus appeared. 120 00:13:08,367 --> 00:13:12,201 But there was another kind of animal hunting in the rivers... 121 00:13:16,647 --> 00:13:18,797 ..birds. 122 00:13:18,967 --> 00:13:22,118 As the platypus grubs around on the river bed, 123 00:13:22,287 --> 00:13:25,438 it attracts fish, which the cormorant snaps up. 124 00:13:31,047 --> 00:13:35,086 Water birds are among the most ancient bird families, 125 00:13:35,247 --> 00:13:39,126 so this could be a scene from just after the death of the dinosaurs, 126 00:13:39,287 --> 00:13:42,404 when a new kind of animal appeared on Earth - 127 00:13:42,567 --> 00:13:46,276 one with warm blood and fur. 128 00:14:08,167 --> 00:14:10,727 The platypus has had enough. 129 00:14:10,887 --> 00:14:13,082 She returns to her breeding burrow, 130 00:14:13,247 --> 00:14:17,240 where, at the end of a tunnel that may be 20 yards long, 131 00:14:17,407 --> 00:14:21,764 safe in a leaf-lined nesting chamber, she's laid an egg. 132 00:14:24,847 --> 00:14:29,398 Exactly what goes on inside a nest, no one really knew. 133 00:14:29,567 --> 00:14:34,243 No one had succeeded in breeding platypus in captivity 134 00:14:34,407 --> 00:14:37,444 until very recently, and certainly no one at all 135 00:14:37,607 --> 00:14:43,284 had seen inside an occupied platypus's nest, until now. 136 00:14:43,447 --> 00:14:47,565 We have bored, very carefully, a hole into the nest 137 00:14:47,727 --> 00:14:51,481 that lies below here and inserted this tube. 138 00:14:51,647 --> 00:14:55,799 This is an optical probe with a little light on the end, 139 00:14:55,967 --> 00:15:00,961 and I can manipulate it like this so that I can scan it. 140 00:15:02,647 --> 00:15:07,243 If I then insert that inside this tube, 141 00:15:07,407 --> 00:15:11,798 I'll be able to see something no one has ever seen before. 142 00:15:14,487 --> 00:15:20,357 That's her in close-up. There's her eye, her ear. 143 00:15:21,727 --> 00:15:23,957 It looks as though she's seen us. 144 00:15:25,127 --> 00:15:27,687 (HE CHUCKLES) 145 00:15:29,327 --> 00:15:32,046 She's...she's nibbling it. 146 00:15:35,447 --> 00:15:37,677 No, not worth eating. 147 00:15:38,927 --> 00:15:42,283 She doesn't seem particularly disturbed by it. 148 00:15:43,927 --> 00:15:46,521 But has her egg hatched? 149 00:15:48,407 --> 00:15:52,559 I think that quivering may have something to do with feeding. 150 00:15:54,527 --> 00:15:58,566 I'll move the camera to see if I can see what's going on. 151 00:15:59,367 --> 00:16:03,042 Yes, there it is...it's milk. 152 00:16:03,407 --> 00:16:06,126 Milk is the perfect food. 153 00:16:06,287 --> 00:16:10,326 It provides the growing youngster with everything it wants. 154 00:16:10,487 --> 00:16:13,763 Only mammals produce milk. 155 00:16:13,927 --> 00:16:17,363 In most mammals, it comes from the nipple, 156 00:16:17,527 --> 00:16:22,885 but in this very primitive mammal, it simply oozes through the skin. 157 00:16:28,847 --> 00:16:33,045 She's leaving. Off she goes. 158 00:16:34,167 --> 00:16:36,681 The end of her furry tail. 159 00:16:39,247 --> 00:16:41,841 What's that among the leaves? 160 00:16:42,487 --> 00:16:46,560 There it is, that's her baby! 161 00:16:49,967 --> 00:16:51,923 I'll try and zoom in on it. 162 00:16:53,407 --> 00:16:58,197 Now you can see it - a tiny grub-like creature, naked and blind. 163 00:16:58,367 --> 00:17:01,404 On the end of its bill you can see a tiny spike. 164 00:17:01,567 --> 00:17:05,003 It's an egg tooth, used to cut through its shell, 165 00:17:05,167 --> 00:17:08,079 in the same way as reptiles and birds do. 166 00:17:11,007 --> 00:17:12,838 Only a few days old. 167 00:17:16,687 --> 00:17:18,678 The platypus and the echidna 168 00:17:18,847 --> 00:17:22,044 are the only mammals alive today that lay eggs, 169 00:17:22,207 --> 00:17:26,405 links with the egg-laying reptiles from which mammals are descended. 170 00:17:26,567 --> 00:17:30,116 Both are so well-adapted to their particular ways of life 171 00:17:30,287 --> 00:17:34,644 that they are still successful and widespread in Australia. 172 00:17:34,807 --> 00:17:36,525 Quite an achievement, 173 00:17:36,687 --> 00:17:39,599 for they've been around for 100 million years, 174 00:17:39,767 --> 00:17:42,645 as the fossil evidence makes clear. 175 00:17:42,807 --> 00:17:46,277 Most of that evidence is just tiny fragments, 176 00:17:46,447 --> 00:17:52,283 but here in Riversleigh in northern Australia, it's a very different story. 177 00:17:55,927 --> 00:17:57,724 Fifty million years ago, 178 00:17:57,887 --> 00:18:00,845 Australia was a much wetter country than it is today, 179 00:18:01,007 --> 00:18:03,885 and just here was then a swampy area. 180 00:18:04,047 --> 00:18:07,357 The bones of animals that died in or around those swamps 181 00:18:07,527 --> 00:18:10,758 became buried in limey mud at the bottom of the pools 182 00:18:10,927 --> 00:18:13,316 and are now preserved in limestone. 183 00:18:17,407 --> 00:18:20,365 This rock is full of bone. 184 00:18:20,527 --> 00:18:25,396 Here's the rectangular bony plate from the back of a crocodile. 185 00:18:25,567 --> 00:18:28,923 The rest looks like bird bone. 186 00:18:29,087 --> 00:18:32,841 The limestone in which they're embedded is so hard 187 00:18:33,007 --> 00:18:35,123 that the only way to get them out 188 00:18:35,287 --> 00:18:38,802 is to put the whole block in a bath of acid for a few weeks. 189 00:18:38,967 --> 00:18:41,720 The limestone then dissolves away, 190 00:18:41,887 --> 00:18:48,156 and what is left is sometimes extraordinary bones, beautifully preserved. 191 00:18:48,327 --> 00:18:52,161 This is the skull of an extinct platypus, 192 00:18:52,327 --> 00:18:54,397 about 15 million years old. 193 00:18:54,567 --> 00:18:59,004 It's been called Obdurodon, which means ''enduring tooth'', 194 00:18:59,167 --> 00:19:04,366 because, unlike today's platypus, which has no teeth, 195 00:19:04,527 --> 00:19:06,802 this one still has them. 196 00:19:06,967 --> 00:19:11,324 There are the empty molar sockets. There, two little pre-molars. 197 00:19:11,487 --> 00:19:15,526 What was this place like 15 million years ago, 198 00:19:15,687 --> 00:19:18,360 when Obdurodon was alive? 199 00:19:37,367 --> 00:19:40,723 The night sky would have been full of the calls of animals 200 00:19:40,887 --> 00:19:43,845 in the surrounding lush tropical forests. 201 00:19:44,567 --> 00:19:50,039 Obdurodon, like the platypus, would swim in the pools. 202 00:19:50,207 --> 00:19:54,598 In the trees around, there were mammals of a different kind - 203 00:19:54,767 --> 00:19:56,598 marsupials. 204 00:19:59,327 --> 00:20:03,115 There were different kinds of possums, similar to those alive today. 205 00:20:05,167 --> 00:20:09,046 On the ground, there were less familiar creatures, 206 00:20:09,207 --> 00:20:11,880 like this large marsupial leaf-eater. 207 00:20:12,047 --> 00:20:14,277 Nothing like it is alive today. 208 00:20:19,527 --> 00:20:22,883 There were great numbers of small mouse-sized animals 209 00:20:23,047 --> 00:20:25,880 which, judging from their teeth, ate insects... 210 00:20:26,767 --> 00:20:29,998 and others with a taste for flesh. 211 00:20:35,407 --> 00:20:40,879 Preying on all these small animals, a marsupial lion. 212 00:20:41,047 --> 00:20:42,560 (GROWLS) 213 00:20:42,727 --> 00:20:47,084 It was big enough to make a meal of an unwary Obdurodon. 214 00:20:55,167 --> 00:20:59,683 As the millions of years passed, Australia began to dry out. 215 00:21:00,967 --> 00:21:05,358 The rainforests retreated and were replaced by grassy plains. 216 00:21:05,527 --> 00:21:09,964 As the landscape changed, so did the marsupial mammals. 217 00:21:10,767 --> 00:21:14,840 They thrived and diversified into many different species 218 00:21:15,007 --> 00:21:17,043 and are still abundant today. 219 00:21:17,207 --> 00:21:21,598 They differ from the platypus and echidna in reproduction. 220 00:21:21,767 --> 00:21:23,723 Instead of laying eggs, 221 00:21:23,887 --> 00:21:26,765 they produce young without protective shells, 222 00:21:26,927 --> 00:21:30,237 and this grey kangaroo is about to do so. 223 00:21:32,087 --> 00:21:34,806 Out comes, not a shelled egg, 224 00:21:34,967 --> 00:21:38,846 but a tiny, under-developed little worm. 225 00:21:59,167 --> 00:22:02,045 It weighs less than a lump of sugar. 226 00:22:02,207 --> 00:22:05,199 It has no back legs but it has forelegs, 227 00:22:05,367 --> 00:22:08,837 just strong enough to pull it through its mother's fur. 228 00:22:09,007 --> 00:22:12,443 It has started on an extraordinary journey. 229 00:22:13,207 --> 00:22:17,519 To survive, it must get to a pouch higher on its mother's belly. 230 00:22:20,007 --> 00:22:23,920 Instinctively, this tiny living particle climbs upwards, 231 00:22:24,087 --> 00:22:28,444 against the pull of gravity, towards the smell of the pouch. 232 00:22:31,367 --> 00:22:33,483 After about three minutes, 233 00:22:33,647 --> 00:22:38,004 it reaches the lip of the pouch and clambers to safety inside. 234 00:22:41,767 --> 00:22:45,965 There it clamps its tiny mouth on its mother's nipple 235 00:22:46,127 --> 00:22:50,086 and takes its first meal, of milk. 236 00:22:51,407 --> 00:22:55,958 As it grows, the ingredients of the milk from the nipple change 237 00:22:56,127 --> 00:22:59,119 to ensure the infant gets exactly the nutrients it needs 238 00:22:59,287 --> 00:23:02,404 for each stage of its development. 239 00:23:05,287 --> 00:23:09,200 By the time it's nine months old, it's getting cramped. 240 00:23:09,367 --> 00:23:12,006 It's time to enter the outside world. 241 00:23:12,167 --> 00:23:15,204 It's almost like a second birth. 242 00:23:22,007 --> 00:23:27,240 He's a little unsteady at first, but Mum offers a helping hand. 243 00:23:34,167 --> 00:23:36,965 Now he's known as a ''joey''. 244 00:23:55,167 --> 00:23:57,635 It's all a bit much for one day 245 00:23:57,807 --> 00:24:01,083 and he heads back to the security of Mother's pouch. 246 00:24:01,247 --> 00:24:04,922 It will be another year before he's fully independent. 247 00:24:10,207 --> 00:24:12,926 (BIRDS CALLING) 248 00:24:14,487 --> 00:24:18,799 Other marsupials have taken to the trees - koalas. 249 00:24:22,087 --> 00:24:24,920 They too have pouches. 250 00:24:30,007 --> 00:24:34,762 It's the Latin word ''marsupium'' - meaning ''pouch or purse'' - 251 00:24:34,927 --> 00:24:38,078 that gives the whole group its name. 252 00:24:38,927 --> 00:24:41,157 When a koala joey emerges, 253 00:24:41,327 --> 00:24:46,526 it clings tight to mother for several days before going solo. 254 00:24:57,647 --> 00:25:02,801 Koalas feed exclusively on the leaves of gum trees, eucalyptus. 255 00:25:02,967 --> 00:25:05,162 They are hardly an ideal food. 256 00:25:05,327 --> 00:25:09,445 They're tough, indigestible and full of unpleasant chemicals. 257 00:25:09,607 --> 00:25:13,361 By sticking close to Mother, they learn how to pick the best trees 258 00:25:13,527 --> 00:25:15,358 with the most palatable leaves. 259 00:25:15,527 --> 00:25:17,916 Even these contain little nourishment, 260 00:25:18,087 --> 00:25:20,760 so they have to eat a lot of them, 261 00:25:20,927 --> 00:25:23,919 and spend almost all their waking hours doing so. 262 00:25:25,807 --> 00:25:30,403 When not feeding, they conserve their energies and sleep. 263 00:25:44,367 --> 00:25:49,361 Only koalas can live on a diet of these particular gum leaves. 264 00:25:49,527 --> 00:25:52,599 Australia seems full of difficult diets in awkward places, 265 00:25:52,767 --> 00:25:56,555 but there are marsupials that can deal with almost every one. 266 00:26:01,407 --> 00:26:06,879 This vast continent stretches from the temperate and sometimes chilly south 267 00:26:07,047 --> 00:26:09,607 right up into the tropics. 268 00:26:12,407 --> 00:26:15,763 In the centre, there are dry sun-baked deserts, 269 00:26:15,927 --> 00:26:19,636 where it's only too easy to die from thirst. 270 00:26:24,607 --> 00:26:29,761 There are great mountain ranges, which in winter are crested with snow. 271 00:26:29,927 --> 00:26:34,478 But the mammalian characteristics of warm blood and insulating fur 272 00:26:34,647 --> 00:26:37,844 enables the marsupials to cope with almost anything. 273 00:26:39,527 --> 00:26:43,600 The wombat's fur is so thick it can remain active 274 00:26:43,767 --> 00:26:48,158 throughout the winter, even in the coldest parts of Australia. 275 00:26:49,967 --> 00:26:52,276 It feeds on grass and other plants, 276 00:26:52,447 --> 00:26:56,235 and the strong front limbs with which it digs itself burrows 277 00:26:56,407 --> 00:26:59,717 are equally good at clearing snow to find food. 278 00:27:07,807 --> 00:27:10,162 Its pouch opens backwards, 279 00:27:10,327 --> 00:27:16,004 so the youngster doesn't get a faceful of snow as Mum digs for food. 280 00:27:21,967 --> 00:27:26,597 Numbats live in woodland, but it can get cold at night 281 00:27:26,767 --> 00:27:31,045 and this family are warming themselves in the early morning sun. 282 00:27:37,647 --> 00:27:42,721 Fur must be in prime condition if it's to function as an insulator, 283 00:27:42,887 --> 00:27:45,959 so grooming is essential. 284 00:27:52,567 --> 00:27:57,083 These dry eucalyptus forests look unpromising as a source of food, 285 00:27:57,247 --> 00:27:59,715 but there are plenty of termites. 286 00:28:00,327 --> 00:28:04,366 Numbats have just the right equipment to collect them. 287 00:28:12,847 --> 00:28:14,803 That spectacular tongue 288 00:28:14,967 --> 00:28:18,960 has to be kept well-anointed with sticky saliva, 289 00:28:19,127 --> 00:28:23,279 and numbats spend some time making quite sure that it is. 290 00:28:31,847 --> 00:28:37,922 With gear like that, a numbat can collect 20,000 termites a day. 291 00:28:41,687 --> 00:28:44,042 This creature's ancestors 292 00:28:44,207 --> 00:28:47,358 might also have used their tongues to collect insects, 293 00:28:47,527 --> 00:28:50,678 but the mammal tongue is an adaptable instrument 294 00:28:50,847 --> 00:28:55,796 and the honey possum uses it to gather pollen and nectar. 295 00:28:56,687 --> 00:28:59,804 It's one of the most specialised feeders of all mammals. 296 00:28:59,967 --> 00:29:02,276 Its tongue has a brush on its tip 297 00:29:02,447 --> 00:29:07,123 which soaks up nectar from even the deepest flowers. 298 00:29:11,127 --> 00:29:15,757 These fields of boulders are home to a less fussy marsupial, 299 00:29:15,927 --> 00:29:19,283 which will collect whatever food happens to be around. 300 00:29:19,447 --> 00:29:21,915 At the moment, there's an unusual delicacy - 301 00:29:22,087 --> 00:29:25,284 these moths, sheltering from the summer sun. 302 00:29:25,447 --> 00:29:30,521 The mountain pygmy possum may be small, but it has a huge appetite. 303 00:29:32,647 --> 00:29:37,846 Moths provide a fast-food snack, high in energy-rich fat, 304 00:29:38,007 --> 00:29:41,443 and it will eat as much as it can while it can get it, 305 00:29:41,607 --> 00:29:46,556 and put on a little fat to see it through leaner times. 306 00:29:48,007 --> 00:29:51,636 Only the indigestible wings are discarded. 307 00:29:53,727 --> 00:29:58,164 At other times of the year, it lives on berries and seeds, 308 00:29:58,327 --> 00:30:01,524 picking them off with its nimble fingers. 309 00:30:06,807 --> 00:30:10,880 The striped possum has a particular taste for grubs. 310 00:30:17,967 --> 00:30:20,925 It lives in the few fragments of rainforest 311 00:30:21,087 --> 00:30:24,159 that survive in north-eastern Australia. 312 00:30:32,167 --> 00:30:34,727 It's got what's necessary to collect them - 313 00:30:34,887 --> 00:30:39,244 an excellent sense of smell, strong teeth to chew the bark 314 00:30:39,407 --> 00:30:41,967 and a long, sticky tongue. 315 00:30:51,727 --> 00:30:56,039 Perhaps the most challenging of all Australian environments 316 00:30:56,207 --> 00:30:59,563 is the arid hot desert at the continent's heart. 317 00:31:02,687 --> 00:31:08,444 Here there is little to eat or drink and few places to hide. 318 00:31:08,607 --> 00:31:11,758 But marsupials have colonised this country too. 319 00:31:21,447 --> 00:31:25,645 Everybody would recognise those as kangaroos. 320 00:31:25,807 --> 00:31:29,436 But the kangaroos belong to a very big family. 321 00:31:29,607 --> 00:31:32,838 There are kangaroos, wallaroos and wallabies, 322 00:31:33,007 --> 00:31:35,840 big ones and small ones. 323 00:31:36,007 --> 00:31:40,080 These are red kangaroos, the biggest of the family, 324 00:31:40,247 --> 00:31:43,956 and they're particularly at home in this dry country. 325 00:31:51,607 --> 00:31:54,804 This can be one of the hottest places on Earth, 326 00:31:54,967 --> 00:31:58,118 so red kangaroos don't have to worry about keeping warm. 327 00:31:58,287 --> 00:32:01,245 Their problem is over-heating. 328 00:32:02,047 --> 00:32:06,723 All mammals sweat to lose heat, but water is in short supply here, 329 00:32:06,887 --> 00:32:10,084 and red kangaroos only do so when they're on the move. 330 00:32:10,807 --> 00:32:13,765 Instead, during the hottest part of the day, 331 00:32:13,927 --> 00:32:17,397 they make use of whatever shade they can find. 332 00:32:18,327 --> 00:32:22,525 Wiping saliva on their forearms helps to lose unwanted heat. 333 00:32:22,687 --> 00:32:25,997 There's a rich supply of blood vessels near the skin surface, 334 00:32:26,167 --> 00:32:29,716 and as the saliva evaporates, the blood cools. 335 00:32:44,727 --> 00:32:48,606 They only feed in the morning and evening when it's cooler. 336 00:32:48,767 --> 00:32:51,076 When they do, it's hard not to notice 337 00:32:51,247 --> 00:32:54,603 the extraordinary way by which they get about. 338 00:32:55,087 --> 00:32:58,159 The tail acts rather like a fifth leg, 339 00:32:58,327 --> 00:33:03,447 propping it up as it swings forwards its huge hind limbs. 340 00:33:10,007 --> 00:33:12,726 It looks ungainly when they're moving slowly, 341 00:33:12,887 --> 00:33:14,878 but when a kangaroo senses danger, 342 00:33:15,047 --> 00:33:19,438 the advantage of these unusual proportions becomes obvious. 343 00:33:29,607 --> 00:33:34,601 Hopping at full speed, a kangaroo can outpace a racehorse. 344 00:33:35,447 --> 00:33:38,041 They're the only large mammals in the world 345 00:33:38,207 --> 00:33:40,926 that have developed this way of getting about, 346 00:33:41,087 --> 00:33:43,999 but it's a very efficient way of doing so. 347 00:33:46,367 --> 00:33:50,565 Tendons in the back legs act like giant springs, 348 00:33:50,727 --> 00:33:52,957 storing energy as it lands, 349 00:33:53,127 --> 00:33:56,676 then releasing it to propel the animal forward again. 350 00:33:56,927 --> 00:33:59,566 By recycling energy like this, 351 00:33:59,727 --> 00:34:02,287 kangaroos can quickly cover vast distances 352 00:34:02,447 --> 00:34:05,678 to escape predators or to search for food and water. 353 00:34:05,847 --> 00:34:09,044 It's not just out on the flat that hopping works well. 354 00:34:09,207 --> 00:34:12,802 Some marsupials even hop around on cliffs. 355 00:34:18,407 --> 00:34:22,446 The rock wallaby's key to success lies in its feet. 356 00:34:29,367 --> 00:34:32,325 The soles have thick corrugated skin, 357 00:34:32,487 --> 00:34:35,638 pads which give them a grip on every kind of surface, 358 00:34:35,807 --> 00:34:40,722 and a wallaby can bounce about this difficult terrain with extraordinary confidence. 359 00:34:52,247 --> 00:34:54,363 There's little to drink here, 360 00:34:54,527 --> 00:34:57,678 and though adults get the fluid they need from their diet, 361 00:34:57,847 --> 00:35:00,919 growing youngsters may find that difficult. 362 00:35:02,527 --> 00:35:06,440 This youngster is after an extra drink from its mother. 363 00:35:06,607 --> 00:35:09,360 They are able to bring up fluid from the stomach 364 00:35:09,527 --> 00:35:11,995 to ensure their young don't go thirsty. 365 00:35:12,167 --> 00:35:15,762 It's a special adaptation to this arid environment. 366 00:35:38,767 --> 00:35:43,841 Grey kangaroos live out on the relatively well-watered grassy plains. 367 00:35:44,007 --> 00:35:48,478 They're among the most sociable of all Australian marsupials. 368 00:35:49,407 --> 00:35:54,435 But living in groups can lead to problems in getting on together. 369 00:36:01,927 --> 00:36:05,715 Last season's joeys are fast approaching independence, 370 00:36:05,887 --> 00:36:09,516 so the mothers will soon be ready to mate again. 371 00:36:22,887 --> 00:36:25,321 Males use their sense of smell 372 00:36:25,487 --> 00:36:28,445 to find out if a female is sexually available, 373 00:36:28,607 --> 00:36:31,565 and will court her for several days. 374 00:36:39,087 --> 00:36:41,681 Having found a promising one, 375 00:36:41,847 --> 00:36:44,566 the male stays close to her side 376 00:36:44,727 --> 00:36:48,925 to try and ensure that he, and no other male, mates with her. 377 00:36:54,087 --> 00:36:57,159 The most dominant male is likely to be the one 378 00:36:57,327 --> 00:36:59,602 to father most of the next generation, 379 00:36:59,767 --> 00:37:02,725 and that is something worth fighting for. 380 00:37:19,927 --> 00:37:22,885 (SNORTS AND BRAYS) 381 00:38:15,447 --> 00:38:19,326 Joeys also fight, but it's just play-boxing, 382 00:38:19,487 --> 00:38:23,116 a way of learning skills that will be important later. 383 00:38:24,087 --> 00:38:27,159 It's not always a fair fight. 384 00:38:30,767 --> 00:38:36,319 Fortunately, this little one still has Mother to see off the neighbourhood bully. 385 00:38:45,727 --> 00:38:49,515 Marsupials first appeared about 100 million years ago, 386 00:38:49,687 --> 00:38:52,679 towards the end of the age of the dinosaurs. 387 00:38:52,847 --> 00:38:56,476 Then Australia was part of a great super-continent. 388 00:38:56,647 --> 00:38:59,400 As the millions of years rolled by, 389 00:38:59,567 --> 00:39:01,956 that continent began to split apart. 390 00:39:02,127 --> 00:39:05,722 One fragment drifted south. That was Antarctica. 391 00:39:05,887 --> 00:39:08,959 As it got closer to the South Pole, so it got colder, 392 00:39:09,127 --> 00:39:13,439 became covered in snow and ice, and its animal inhabitants died out. 393 00:39:13,607 --> 00:39:15,802 A second part was Australia. 394 00:39:15,967 --> 00:39:21,439 It drifted north and got warmer and marsupials flourished. 395 00:39:21,607 --> 00:39:26,123 There was a third part. It too drifted north. 396 00:39:26,287 --> 00:39:29,916 It too had marsupials, and they're still there. 397 00:39:30,087 --> 00:39:32,885 That was South America. 398 00:39:37,167 --> 00:39:40,603 It may have been in this region of the super-continent 399 00:39:40,767 --> 00:39:43,361 that the marsupial mammals first appeared. 400 00:39:43,527 --> 00:39:47,315 Many died out, but there are still a lot of survivors. 401 00:39:50,047 --> 00:39:52,925 This is one of the most elusive of them. 402 00:39:53,087 --> 00:39:57,444 Living in the Amazon forest streams, it operates only at night, 403 00:39:57,607 --> 00:40:00,519 moving in the pitch blackness by feeling its way 404 00:40:00,687 --> 00:40:03,679 with its front paws and luxuriant whiskers. 405 00:40:03,847 --> 00:40:06,964 It's the yapok, or water opossum. 406 00:40:11,767 --> 00:40:15,043 These pictures, taken with infra-red cameras, 407 00:40:15,207 --> 00:40:19,439 may be the first time it's been filmed in its natural environment. 408 00:40:20,887 --> 00:40:24,516 It's hunting for fish and crustaceans. 409 00:40:24,687 --> 00:40:29,238 Its fur is so thick that its skin doesn't get wet. 410 00:40:29,407 --> 00:40:33,241 It has webbed feet to propel it through the water. 411 00:40:42,087 --> 00:40:46,080 It's too dark for even the sharpest eyes to see very much. 412 00:40:46,247 --> 00:40:52,163 The yapok relies on its acute sense of smell and hearing to locate its food. 413 00:40:52,847 --> 00:40:55,156 It swims with its arms apart, 414 00:40:55,327 --> 00:40:59,718 groping for its prey with its highly sensitive fingers. 415 00:41:10,207 --> 00:41:12,004 It usually takes its catch 416 00:41:12,167 --> 00:41:16,638 to the shelter of nearby vegetation to devour it. 417 00:41:19,807 --> 00:41:22,401 It doesn't only feed in the shallows. 418 00:41:22,567 --> 00:41:24,558 The yapok has a large territory, 419 00:41:24,727 --> 00:41:27,685 and there are many deeper pools in which to swim. 420 00:41:38,847 --> 00:41:43,557 Under water, it swims with its eyes shut, like the platypus, 421 00:41:43,727 --> 00:41:46,241 and hunts entirely by feel. 422 00:41:47,327 --> 00:41:51,002 The female yapok can also shut her pouch, 423 00:41:51,167 --> 00:41:53,761 and does so with such muscular strength 424 00:41:53,927 --> 00:41:57,078 that water doesn't get in and drown her babies, 425 00:41:57,247 --> 00:42:01,877 though they must be close to suffocation after a few minutes of fishing. 426 00:42:07,767 --> 00:42:12,636 After a good night's hunting, the yapok retreats as day breaks. 427 00:42:23,887 --> 00:42:27,641 The yapok is the only aquatic marsupial in the world. 428 00:42:27,807 --> 00:42:30,924 Most marsupials in Central and South America 429 00:42:31,087 --> 00:42:34,204 live high in the canopy of the rainforest. 430 00:42:34,367 --> 00:42:37,996 Just how many there are up there, no one suspected 431 00:42:38,167 --> 00:42:42,285 until scientists started using cranes, like this one. 432 00:42:47,207 --> 00:42:51,758 Such apparatus gives easy access to this high canopy. 433 00:42:51,927 --> 00:42:57,206 We can now get an accurate idea of how rich wildlife is up here. 434 00:42:58,327 --> 00:43:02,320 We might think of Australia as the land of the marsupials, 435 00:43:02,487 --> 00:43:04,762 but this canopy of the rainforest 436 00:43:04,927 --> 00:43:08,602 may have more of them than any other kind of mammal. 437 00:43:12,487 --> 00:43:17,117 Most are strictly nocturnal and, though they are abundant, 438 00:43:17,287 --> 00:43:22,042 they, like everything else in the forest, can be difficult to spot. 439 00:43:24,847 --> 00:43:27,042 Many are similar to this woolly opossum - 440 00:43:27,207 --> 00:43:29,641 tree dwellers with few specialisations 441 00:43:29,807 --> 00:43:34,323 and a broad diet which can include flowers, fruit and insects. 442 00:43:44,087 --> 00:43:46,840 These marsupial mammals, of course, 443 00:43:47,007 --> 00:43:50,886 reproduce in the same way as their Australian relatives. 444 00:43:51,047 --> 00:43:53,038 They give birth to tiny babies 445 00:43:53,207 --> 00:43:56,005 at a very early stage in their development. 446 00:43:56,167 --> 00:44:00,604 The pouch is seldom as well-formed as that of a kangaroo or koala, 447 00:44:00,767 --> 00:44:03,235 but their young survive very well, 448 00:44:03,407 --> 00:44:06,558 clinging unprotected to their mother's underside. 449 00:44:16,127 --> 00:44:19,005 Marsupial mammals dominate Australia 450 00:44:19,167 --> 00:44:22,159 and flourish in the forests of Central and South America. 451 00:44:22,327 --> 00:44:26,798 Alongside them lives a radically different kind of mammal, 452 00:44:26,967 --> 00:44:29,606 a kind to which we ourselves belong. 453 00:44:29,767 --> 00:44:35,160 And it's only that kind that you find everywhere else in the world. 454 00:44:37,487 --> 00:44:41,275 The plains of Africa have an abundance of mammals, 455 00:44:41,447 --> 00:44:43,677 but not one is a marsupial. 456 00:44:43,847 --> 00:44:47,362 They all reproduce in a fundamentally different way. 457 00:44:47,527 --> 00:44:51,122 This wildebeest has nourished her baby within her 458 00:44:51,287 --> 00:44:56,077 by means of a remarkable organ growing on the wall of her womb, a placenta - 459 00:44:56,247 --> 00:44:59,239 a circular pad, rich in blood vessels, 460 00:44:59,407 --> 00:45:03,719 connected to her baby by a cable, the umbilical cord, 461 00:45:03,887 --> 00:45:07,880 through which she has fed her growing youngster. 462 00:45:08,567 --> 00:45:12,560 The baby's blood vessels run through the cords of the placenta, 463 00:45:12,727 --> 00:45:17,005 passing so close to its mother's, they absorb nutrients from her blood 464 00:45:17,167 --> 00:45:20,318 and carry it back to the unborn infant. 465 00:45:21,247 --> 00:45:24,364 But all this is about to change. 466 00:45:31,687 --> 00:45:35,362 Giving birth to such a large, highly-developed baby 467 00:45:35,527 --> 00:45:37,802 places great strains on the mother. 468 00:45:41,087 --> 00:45:44,079 It's pretty traumatic for the baby too. 469 00:45:48,087 --> 00:45:51,762 But there is a great advantage in being born this way. 470 00:45:51,927 --> 00:45:55,806 There are plenty of animals around for whom a new-born calf 471 00:45:55,967 --> 00:45:58,356 would make a welcome meal. 472 00:46:00,247 --> 00:46:04,445 But this mammal baby, reared with the help of a placenta, 473 00:46:04,607 --> 00:46:08,964 is able to get to its feet within minutes of its birth. 474 00:46:17,447 --> 00:46:22,919 While it's finding its balance, its mother is there to defend it. 475 00:46:24,247 --> 00:46:27,080 (MOTHER BRAYS AND BELLOWS) 476 00:46:38,407 --> 00:46:43,276 Now the baby can be fed in the same way as all mammal babies, 477 00:46:43,447 --> 00:46:45,961 with its mother's milk. 478 00:46:58,847 --> 00:47:03,796 Placental babies may still have months, even years to go 479 00:47:03,967 --> 00:47:06,162 before they are fully independent, 480 00:47:06,367 --> 00:47:10,246 but the early months, protected in their mother's body, 481 00:47:10,407 --> 00:47:14,685 have given these babies an invaluable start in life. 482 00:47:18,887 --> 00:47:23,324 Whether mammals lay eggs or give birth to live young, 483 00:47:23,487 --> 00:47:27,719 whether their babies develop in a womb or in a pouch, 484 00:47:27,887 --> 00:47:31,323 they've managed to live almost everywhere. 485 00:47:35,887 --> 00:47:38,242 (BIRDS SQUAWK) 486 00:47:57,567 --> 00:48:02,322 The warm-blooded, furry, milk-producing mammalian body, 487 00:48:02,487 --> 00:48:05,684 in all its multitudinous variations, 488 00:48:05,847 --> 00:48:09,522 really is a winning design.