1
00:00:02,202 --> 00:00:04,568
In the last episode of
Walking with Monsters,

2
00:00:04,771 --> 00:00:08,036
our earliest fish ancestors
escaped their armoured enemies,

3
00:00:08,241 --> 00:00:09,936
the Arthropods.

4
00:00:10,543 --> 00:00:14,877
They evolved legs and lungs
and took their first steps onto land.

5
00:00:18,051 --> 00:00:20,884
But not far enough
from the perils of the water.

6
00:00:22,055 --> 00:00:26,219
Now our amphibian ancestors
have made another huge leap forward.

7
00:00:27,660 --> 00:00:30,561
They've evolved into the first reptiles.

8
00:00:33,266 --> 00:00:35,860
But they will face other giants.

9
00:00:36,069 --> 00:00:39,061
Monsters who consider this their turf.

10
00:00:40,740 --> 00:00:43,937
The war for the world
has moved on to dry land.

11
00:00:44,411 --> 00:00:47,005
The Arthropods are back.

12
00:01:23,016 --> 00:01:25,541
Three hundred million years ago

13
00:01:25,785 --> 00:01:30,279
much of the Earth
was covered in vast swamp forests.

14
00:01:33,493 --> 00:01:36,462
Here, nothing is as it seems.

15
00:01:37,697 --> 00:01:42,862
The fifty metre giants towering above
this water world may look like trees,

16
00:01:43,069 --> 00:01:46,368
but they're actually
distant relatives of ferns.

17
00:01:50,844 --> 00:01:53,108
Even the air is alien.

18
00:01:53,780 --> 00:01:55,839
Over a third is oxygen.

19
00:01:56,049 --> 00:01:59,109
Much higher than at any time in history.

20
00:01:59,319 --> 00:02:03,221
This oxygen rich atmosphere
has fuelled the growth of new,

21
00:02:03,423 --> 00:02:06,654
super sized Arthropod predators.

22
00:02:15,435 --> 00:02:19,235
This Mesothelae spider
is the size of a human head.

23
00:02:19,506 --> 00:02:22,304
She'd be hunting cats
if she were alive today.

24
00:02:25,778 --> 00:02:27,575
She's an ambush predator.

25
00:02:27,780 --> 00:02:30,806
Operating from her
underground headquarters.

26
00:02:34,554 --> 00:02:35,748
Safe in her borrow,

27
00:02:35,955 --> 00:02:39,914
she rests her feet
on carefully constructed trip lines.

28
00:02:41,728 --> 00:02:45,528
These allow her to pick up vibrations
from the outside world.

29
00:02:59,279 --> 00:02:59,938
Reptile,

30
00:03:00,146 --> 00:03:03,547
Petrolacosaurus is hunting
on the forest floor.

31
00:03:05,818 --> 00:03:07,877
Unlike our amphibian ancestors,

32
00:03:08,087 --> 00:03:12,547
he has tough scaly skin
which traps moisture inside his body.

33
00:03:12,759 --> 00:03:14,989
Vital for all land dwellers.

34
00:03:15,929 --> 00:03:17,954
Because he doesn't dry out in the sun,

35
00:03:18,164 --> 00:03:20,598
he can venture away from water.

36
00:03:21,768 --> 00:03:24,794
But that means
encountering new predators.

37
00:03:49,929 --> 00:03:52,591
The reptile outruns the spider.

38
00:03:55,134 --> 00:03:57,159
He's evolved a complex heart,

39
00:03:57,370 --> 00:03:59,270
much more efficient than his enemy's.

40
00:03:59,472 --> 00:04:01,599
In fact the template for our own.

41
00:04:01,808 --> 00:04:06,609
It's a powerful pump that pushes blood
and oxygen around his body to his muscles,

42
00:04:06,813 --> 00:04:10,374
so he can run at high speed
without stopping for a rest.

43
00:04:13,920 --> 00:04:16,912
This time though
he's trapped inside a log.

44
00:04:29,736 --> 00:04:32,933
At first the spider's armour
stops her squeezing in.

45
00:04:34,774 --> 00:04:37,504
But she's not going to give up so easily.

46
00:04:53,593 --> 00:04:54,651
Back in her lair,

47
00:04:54,861 --> 00:04:58,353
Mesothelae will inject her victim
with digestive juices

48
00:04:58,564 --> 00:05:00,998
to dissolve him from inside.

49
00:05:07,607 --> 00:05:10,770
There are other dangers in the swamp
apart from predators.

50
00:05:10,977 --> 00:05:13,377
The water levels can change rapidly.

51
00:05:15,048 --> 00:05:16,447
They've risen.

52
00:05:21,387 --> 00:05:25,551
The spider drags her dinner home,
but something's wrong.

53
00:05:32,865 --> 00:05:34,355
Her headquarters are flooding.

54
00:05:34,567 --> 00:05:36,398
She'll have to evacuate.

55
00:05:38,471 --> 00:05:42,202
She can't dig, so she'll have to
find another hole she can adapt.

56
00:05:44,010 --> 00:05:48,208
And once outside,
she's vulnerable to larger predators.

57
00:05:55,621 --> 00:05:58,283
Meganeurid is a monster dragon fly,

58
00:05:58,491 --> 00:06:01,153
queen of the carboniferous skies.

59
00:06:04,097 --> 00:06:05,894
With a wing span of almost a metre,

60
00:06:06,099 --> 00:06:09,728
she's the size of an eagle
with an appetite to match.

61
00:06:16,542 --> 00:06:18,737
High above her carboniferous kingdom,

62
00:06:18,945 --> 00:06:21,175
normally she's invincible.

63
00:06:21,748 --> 00:06:23,739
But trouble's brewing.

64
00:06:24,984 --> 00:06:27,976
The flood below
is due to an approaching storm.

65
00:06:28,821 --> 00:06:30,846
The super oxygenated atmosphere,

66
00:06:31,057 --> 00:06:33,150
which has helped
fuel the growth of the insects,

67
00:06:33,359 --> 00:06:36,294
the Arthropods, is highly volatile.

68
00:06:36,662 --> 00:06:39,358
A lightning strike
could trigger an explosion.

69
00:06:41,401 --> 00:06:43,733
The clock is ticking for the swamp.

70
00:06:48,808 --> 00:06:52,005
The rising water levels
suit one group of hunters.

71
00:06:53,012 --> 00:06:54,240
Amphibians.

72
00:06:54,447 --> 00:06:57,848
They've continued thriving
over the last sixty million years.

73
00:06:58,751 --> 00:07:02,278
Their thin skin still restrict them
to the water's edge,

74
00:07:02,588 --> 00:07:07,048
but they're now powerful predators
with a devastating pair of jaws,

75
00:07:07,260 --> 00:07:10,491
ready to ambush anything
that wanders within reach.

76
00:07:17,303 --> 00:07:20,602
The homeless spider
tries her luck further inland.

77
00:07:21,641 --> 00:07:24,303
But other Mesothelae
fill the forest floor

78
00:07:24,510 --> 00:07:26,808
and they don't like to share.

79
00:07:32,418 --> 00:07:34,409
Neither does Arthropleura.

80
00:07:34,620 --> 00:07:37,145
He's a distant relative
of modern millipedes,

81
00:07:37,356 --> 00:07:39,221
but as long as a car.

82
00:07:41,294 --> 00:07:44,593
He can rear up,
tall enough to look you right in the eye.

83
00:07:46,098 --> 00:07:47,531
Although he's vegetarian,

84
00:07:47,733 --> 00:07:51,191
his strong jaws
could still deliver a nasty bite.

85
00:08:00,947 --> 00:08:02,278
With rising waters,

86
00:08:02,482 --> 00:08:06,578
Arthropleura's foraging leads him
into dangerous territory.

87
00:08:33,513 --> 00:08:35,378
In this clash of the titans,

88
00:08:35,581 --> 00:08:38,311
the Arthropod's armour
is his best defence.

89
00:08:45,892 --> 00:08:47,985
Unless it gets split.

90
00:08:57,837 --> 00:09:01,500
Impaled, his soft innards provide a feast.

91
00:09:05,778 --> 00:09:09,908
The lightning storm is building,
moving ever closer.

92
00:09:11,984 --> 00:09:15,476
Just in time,
the spider finds another hole.

93
00:09:18,291 --> 00:09:20,259
A Petrolacosaurus is evicted,

94
00:09:20,459 --> 00:09:23,087
but reptiles don't need
burrows to avoid danger,

95
00:09:23,296 --> 00:09:25,992
they have speed
and stamina on their side.

96
00:09:29,201 --> 00:09:33,160
Meanwhile, the spider starts
to turn the hole into a hunter's lair.

97
00:09:45,518 --> 00:09:46,883
Night falls.

98
00:09:48,287 --> 00:09:52,087
And Mesothelae settles
into her new silk-lined home

99
00:09:53,693 --> 00:09:56,127
She tests the new trip lines.

100
00:09:56,395 --> 00:09:59,296
They're already picking up
vibrations from outside.

101
00:10:00,933 --> 00:10:02,901
The storm is very close now.

102
00:10:06,205 --> 00:10:09,072
Lightning strikes ignite
the oxygen rich air.

103
00:10:12,378 --> 00:10:16,337
The giant dragonflies are forced down
from the canopy to seek shelter below.

104
00:10:19,118 --> 00:10:22,178
An unexpected windfall
for the water predators.

105
00:10:36,736 --> 00:10:37,600
Amid the chaos,

106
00:10:37,803 --> 00:10:41,637
Mesothelae seems safe
in her bunker underground.

107
00:10:58,090 --> 00:11:00,524
A huge fire, ignited by lightning,

108
00:11:00,726 --> 00:11:03,422
has devastated Mesothelae's neighbourhood.

109
00:11:09,101 --> 00:11:11,899
There are no signs of life above ground.

110
00:11:18,944 --> 00:11:23,176
However, a Petrolacosaurus managed
to outrun the flames.

111
00:11:25,151 --> 00:11:28,120
But now he heads
right into the spider's lair.

112
00:11:42,968 --> 00:11:46,768
Mesothelae's hole was at
the centre of the lightning strike.

113
00:11:52,344 --> 00:11:55,541
The reptile gets a spider barbecue.

114
00:11:58,818 --> 00:12:01,981
The era of the giant bugs
is coming to an end.

115
00:12:02,354 --> 00:12:05,881
The climate is drying
and the atmosphere is losing oxygen.

116
00:12:06,325 --> 00:12:10,284
The monster insects
and spiders can't survive the change.

117
00:12:13,099 --> 00:12:15,761
But with their efficient hearts
and waterproof skin,

118
00:12:15,968 --> 00:12:20,268
our versatile ancestors flourish
in the new dry climate.

119
00:12:22,141 --> 00:12:24,575
Evolution takes over.

120
00:12:27,113 --> 00:12:28,603
Lacking restrictive armour

121
00:12:28,814 --> 00:12:31,908
means the reptiles
can start to make it big.

122
00:12:36,222 --> 00:12:39,817
Their muscles and bones
broaden and extend.

123
00:12:42,228 --> 00:12:47,131
Their bodies mushroom into
huge new shapes and forms.

124
00:12:48,701 --> 00:12:51,966
Our distant ancestors
have come a long way.

125
00:12:52,404 --> 00:12:54,804
They've now conquered the land.

126
00:13:04,784 --> 00:13:08,652
The world's first
giant reptiles have arrived.

127
00:13:09,088 --> 00:13:11,113
But they're not related to dinosaurs.

128
00:13:11,323 --> 00:13:15,282
Their descendents will be
of a very different kind.

129
00:13:25,171 --> 00:13:28,732
Reptiles have now
spread all across the globe.

130
00:13:34,914 --> 00:13:38,111
Edaphosaurus bask
in the early morning sun.

131
00:13:39,785 --> 00:13:42,583
They're three metres long,
as big as hippos,

132
00:13:42,788 --> 00:13:45,518
and, like them, they're vegetarians.

133
00:13:52,364 --> 00:13:57,063
Life in their new Permian home
is a constant battle with the elements.

134
00:13:58,904 --> 00:14:02,101
The climate swings
between seasonal extremes.

135
00:14:02,308 --> 00:14:06,039
From burning summers,
to freezing winters.

136
00:14:09,815 --> 00:14:11,840
A new species of plant has evolved,

137
00:14:12,051 --> 00:14:15,487
able to withstand this cold,
dry atmosphere.

138
00:14:16,422 --> 00:14:18,219
Primitive conifers.

139
00:14:22,127 --> 00:14:23,253
In this harsh world,

140
00:14:23,462 --> 00:14:26,693
creatures need ways
to regulate their body temperature.

141
00:14:27,066 --> 00:14:30,194
Edaphosaurus are sluggish
autumn morning chill,

142
00:14:30,402 --> 00:14:32,336
but they'll soon warm up.

143
00:14:33,138 --> 00:14:35,936
Thanks to the huge sail on their backs.

144
00:14:39,278 --> 00:14:44,739
Their backbone has tall spines connected by
a thin membrane of blood filled skin.

145
00:14:46,252 --> 00:14:51,485
This large surface area can lose heat fast,
if the Edaphosaurus need to cool down.

146
00:14:54,560 --> 00:14:55,584
While to heat up,

147
00:14:55,794 --> 00:14:58,490
they simply turn
their sails towards the sun,

148
00:14:58,697 --> 00:15:00,665
like a solar panel.

149
00:15:07,172 --> 00:15:11,006
Amazingly, these strange sailbacks
are related to us.

150
00:15:11,210 --> 00:15:15,874
They're part of a very special group
of creatures called mammal like reptiles.

151
00:15:16,081 --> 00:15:20,518
It's down to them that we have control
over our body temperature today.

152
00:15:27,459 --> 00:15:30,257
But Edphosaurus aren't
the only sailbacks,

153
00:15:30,462 --> 00:15:33,989
and now their biggest enemy
is one of their own kind.

154
00:15:45,911 --> 00:15:49,642
This is Dimetrodon, a vicious carnivore.

155
00:15:49,848 --> 00:15:52,282
The biggest reptile on Earth.

156
00:15:56,255 --> 00:15:58,883
She'd normally attack adult Edaphosaurus,

157
00:15:59,091 --> 00:16:01,321
but today she wants to avoid injury.

158
00:16:01,527 --> 00:16:05,054
She's pregnant and almost ready
to lay her eggs.

159
00:16:08,400 --> 00:16:11,426
She finds a smaller, softer target.

160
00:16:34,693 --> 00:16:36,354
This was only a mock charge,

161
00:16:36,562 --> 00:16:40,623
a tactic to disperse the group
and expose the vulnerable young.

162
00:16:42,101 --> 00:16:45,195
The panicking Edaphosaurus
flush their sails with blood,

163
00:16:45,404 --> 00:16:48,032
flashing an eye spot
to distract the predator's attention

164
00:16:48,240 --> 00:16:50,071
from their vulnerable head.

165
00:16:51,610 --> 00:16:54,408
But Dimetrodon can see
through their disguise.

166
00:17:15,200 --> 00:17:17,498
She locks on to her victim.

167
00:17:40,092 --> 00:17:42,492
As well as her sheer size and power,

168
00:17:42,694 --> 00:17:45,492
Dimetrodon has a killer edge.

169
00:17:47,166 --> 00:17:51,432
As a mammal like reptile,
she's evolved specialised teeth.

170
00:17:51,970 --> 00:17:54,666
Incisors shear off chunks of flesh.

171
00:17:55,074 --> 00:17:57,565
Serrated canines cut and slice.

172
00:17:58,010 --> 00:18:01,241
We humans have inherited
these same meat eating teeth.

173
00:18:02,614 --> 00:18:05,583
We have a smaller version
in our mouths today.

174
00:18:08,887 --> 00:18:11,981
The young Edaphosaurus
didn't stand a chance.

175
00:18:14,026 --> 00:18:16,688
This is a crucial kill
for the Dimetrodon.

176
00:18:16,895 --> 00:18:17,623
Before she lays

177
00:18:17,830 --> 00:18:21,231
she needs to eat enough
to last her for the next seven months.

178
00:18:21,967 --> 00:18:24,060
To boost her babies chances of survival,

179
00:18:24,269 --> 00:18:27,329
she's evolved a basic form of parental care.

180
00:18:27,773 --> 00:18:29,331
Guarding her eggs.

181
00:18:30,175 --> 00:18:33,269
But the smell of blood
has attracted more Dimetrodon.

182
00:18:34,213 --> 00:18:36,545
Highly aggressive males.

183
00:18:50,362 --> 00:18:53,763
The female knows better
than to defend her kill.

184
00:18:56,235 --> 00:18:57,964
By the time the group has finished

185
00:18:58,170 --> 00:19:00,229
there'll be nothing left but bones.

186
00:19:04,276 --> 00:19:07,973
While lions today consume
seventy per cent of a carcass,

187
00:19:08,180 --> 00:19:10,546
Dimetrodon eat ninety.

188
00:19:13,385 --> 00:19:17,515
But they'll only eat intestines
after shaking out the waste inside.

189
00:19:18,524 --> 00:19:21,925
Dung is one thing
a Dimetrodon can't stomach.

190
00:19:38,043 --> 00:19:41,740
The female has built
a nesting mound of earth and wood.

191
00:19:51,590 --> 00:19:54,320
Inside, she digs a deep burrow.

192
00:20:02,901 --> 00:20:05,028
And starts to lay her eggs.

193
00:20:17,482 --> 00:20:22,010
She covers her brood carefully,
ready to begin her guard duty.

194
00:20:24,456 --> 00:20:27,186
Egg thieves lurk in the shadows.

195
00:20:29,761 --> 00:20:32,286
Like this carnivorous amphibian.

196
00:20:32,798 --> 00:20:35,596
But he's too small
to make a full frontal attack.

197
00:20:35,801 --> 00:20:39,362
He'll have to bide his time
until the female turns her back.

198
00:20:42,241 --> 00:20:45,802
The mother must also
constantly monitor the nest's temperature.

199
00:20:48,614 --> 00:20:52,345
Temperature control is vital
for reptiles even before they hatch.

200
00:20:54,052 --> 00:20:57,419
The mother piles on more earth
if the babies are too cold.

201
00:20:58,857 --> 00:21:03,794
And will remove a layer if they're too warm,
otherwise the babies will die.

202
00:21:10,168 --> 00:21:12,659
It's going to be a long seven months.

203
00:21:26,618 --> 00:21:28,916
As autumn turns to bitterly cold winter,

204
00:21:30,555 --> 00:21:32,648
the landscape is transformed.

205
00:21:35,560 --> 00:21:38,222
Still the female keeps her vigil,

206
00:21:39,031 --> 00:21:42,364
getting weaker all the time
from lack of food.

207
00:21:52,411 --> 00:21:56,211
Until finally winter melts into spring.

208
00:22:04,956 --> 00:22:06,355
With the warmer weather,

209
00:22:06,558 --> 00:22:09,618
the Edaphosaurus laze
beneath the conifers,

210
00:22:09,828 --> 00:22:13,264
shading their sails from the sun
to avoid overheating.

211
00:22:19,471 --> 00:22:21,962
But there's much activity
at the nesting mound.

212
00:22:22,974 --> 00:22:25,306
And it's not the mother who's digging.

213
00:22:27,779 --> 00:22:30,873
Another female is desperate to lay her eggs.

214
00:22:35,554 --> 00:22:36,987
If she takes over the mound,

215
00:22:37,189 --> 00:22:40,955
she'll dig out and kill
the incubating young already inside.

216
00:22:47,232 --> 00:22:49,097
The resident mother may be weak,

217
00:22:49,301 --> 00:22:51,861
but she won't give up
her nest without a fight.

218
00:23:11,456 --> 00:23:14,448
It's a battle neither can afford to lose.

219
00:23:41,820 --> 00:23:45,847
Next morning, just one female
remains at the nesting mound.

220
00:23:52,264 --> 00:23:56,667
It's the resident mother.
She's managed to wrestle off her rival.

221
00:23:58,537 --> 00:24:00,562
But not without a sacrifice.

222
00:24:01,506 --> 00:24:05,909
She won't be able to defend her eggs
or herself for much longer.

223
00:24:08,747 --> 00:24:12,979
And the thieving amphibian
is poised to seize his chance.

224
00:24:22,627 --> 00:24:26,825
As summer arrives,
the Edaphosaurus are thriving in the heat.

225
00:24:31,837 --> 00:24:35,898
The young have grown
and test out their newfound strength.

226
00:24:45,317 --> 00:24:48,684
But the mother Dimetrodon
has reached the end of hers.

227
00:24:50,956 --> 00:24:55,052
So weak, she's helpless as
another intruder attacks her nest.

228
00:25:00,165 --> 00:25:02,258
Luckily this large male has got his teeth

229
00:25:02,467 --> 00:25:07,495
into something more substantial
than her young. The amphibian.

230
00:25:12,811 --> 00:25:16,144
The precious eggs are safe
and ready to hatch.

231
00:25:18,250 --> 00:25:20,218
The mother can hear them squeaking.

232
00:25:20,418 --> 00:25:22,249
She's achieved her goal.

233
00:25:24,289 --> 00:25:27,122
But at this moment
her maternal bond is severed.

234
00:25:27,459 --> 00:25:31,088
Unlike her mammal descendents,
she won't nurture her young.

235
00:25:31,663 --> 00:25:35,793
Her instinct now is to save herself,
by finding food.

236
00:25:59,224 --> 00:26:01,055
Without their mother's protection,

237
00:26:01,259 --> 00:26:04,057
the babies will have to
be ready to go it alone.

238
00:26:06,698 --> 00:26:10,099
They take their first steps into a perilous world

239
00:26:10,535 --> 00:26:13,834
and must make a mad dash
for the safety of the trees.

240
00:26:20,712 --> 00:26:23,840
A danger in a familiar form awaits them.

241
00:26:26,117 --> 00:26:29,086
Adult Dimetrodon are cannibals.

242
00:26:48,740 --> 00:26:50,765
Not all babies are helpless.

243
00:26:50,976 --> 00:26:54,537
Some already instinctively know
how to defend themselves.

244
00:26:57,515 --> 00:27:02,316
They roll in dung.
Something the adults can't stand.

245
00:27:03,421 --> 00:27:06,754
Repelling their pursuers
long enough to get a head start.

246
00:27:28,346 --> 00:27:31,975
One adult is driven on
by hunger and desperation.

247
00:27:32,617 --> 00:27:37,145
The mother.
She'll weed out weaker babies straight away,

248
00:27:37,355 --> 00:27:41,758
which helps the strong ones
and her species as a whole survive.

249
00:27:42,861 --> 00:27:46,763
And now the reptiles evolve
to tighten their grip on land.

250
00:27:51,970 --> 00:27:54,131
Their legs straighten and lengthen,

251
00:27:54,406 --> 00:27:57,034
holding them more upright
and giving them speed.

252
00:27:59,377 --> 00:28:04,508
Their backbones and muscles get stronger
and they even start to look like mammals.

253
00:28:08,186 --> 00:28:13,021
To house a larger brain
their skull bones expand into an enormous head.

254
00:28:13,591 --> 00:28:17,083
And out of their draw thrust huge, sharp teeth.

255
00:28:19,364 --> 00:28:22,800
A new age of specialist reptiles had dawned.

256
00:28:31,376 --> 00:28:33,344
Next time on Walking with Monsters,

257
00:28:33,545 --> 00:28:37,208
we enter the world of
the first terrifying sabre tooth,

258
00:28:37,415 --> 00:28:40,316
but find it always size that counts.

259
00:28:42,253 --> 00:28:45,814
And we meet one of the most
successful reptiles of all time

260
00:28:46,024 --> 00:28:48,288
who face a perilous journey.

261
00:28:50,361 --> 00:28:53,296
Back to the dangers of the water.