1
00:00:01,068 --> 00:00:03,269
Viewers like you make
this program possible.

2
00:00:03,270 --> 00:00:05,339
Support your local PBS station.

3
00:00:14,382 --> 00:00:16,049
NARRATOR:
Mammals.

4
00:00:16,050 --> 00:00:18,585
They live in almost every corner
of the planet.

5
00:00:18,586 --> 00:00:20,754
Thousands of different species.

6
00:00:20,755 --> 00:00:22,689
(squeaking)

7
00:00:22,690 --> 00:00:23,990
From tiny desert creatures

8
00:00:23,991 --> 00:00:26,092
to giant ocean beasts

9
00:00:26,093 --> 00:00:27,694
to us.

10
00:00:27,695 --> 00:00:30,231
But when did our shared history
begin?

11
00:00:31,899 --> 00:00:33,166
(impact echoes)

12
00:00:33,167 --> 00:00:35,268
You might think
the start of the mammal story

13
00:00:35,269 --> 00:00:37,404
was the extinction
of the dinosaurs

14
00:00:37,405 --> 00:00:39,072
some 66 million years ago...

15
00:00:39,073 --> 00:00:40,640
(squeaking)

16
00:00:40,641 --> 00:00:45,278
{\an8}...but the story actually begins
much, much earlier...

17
00:00:45,279 --> 00:00:46,713
We have the very earliest
ancestors of mammals.

18
00:00:46,714 --> 00:00:49,682
Those animals
are four times as old

19
00:00:49,683 --> 00:00:50,918
as the oldest T. rex.

20
00:00:52,920 --> 00:00:55,789
NARRATOR:
...in a time when mysterious
animals ruled.

21
00:00:55,790 --> 00:00:57,657
They looked very different
from anything alive today.

22
00:00:57,658 --> 00:01:00,460
NARRATOR:
In some ways,

23
00:01:00,461 --> 00:01:01,861
they looked like reptiles.

24
00:01:01,862 --> 00:01:03,897
But it's from here
that mammals took shape...

25
00:01:03,898 --> 00:01:05,098
They were our ancestors.

26
00:01:05,099 --> 00:01:08,101
NARRATOR:
...surviving a tumultuous period

27
00:01:08,102 --> 00:01:09,836
in Earth's history.

28
00:01:09,837 --> 00:01:11,271
MIKE DAY:
It became apparent

29
00:01:11,272 --> 00:01:12,472
that there were
two extinction events.

30
00:01:12,473 --> 00:01:14,207
Our ancestors made it through

31
00:01:14,208 --> 00:01:15,875
for very specific reasons.

32
00:01:15,876 --> 00:01:18,011
We had very specific adaptations
as a group,

33
00:01:18,012 --> 00:01:21,414
and that allowed us to make it
past these extinction events.

34
00:01:21,415 --> 00:01:24,050
{\an8}NARRATOR:
What was the secret
to our ancestors' survival

35
00:01:24,051 --> 00:01:25,952
in the face
of deadly catastrophes?
(thunder claps)

36
00:01:25,953 --> 00:01:27,454
♪ ♪

37
00:01:27,455 --> 00:01:29,956
"Mammal Origins."

38
00:01:29,957 --> 00:01:33,026
Right now, on "NOVA."

39
00:01:33,027 --> 00:01:37,064
♪ ♪

40
00:01:49,176 --> 00:01:50,176
(growling softly)

41
00:01:50,177 --> 00:01:51,511
NARRATOR:
Mammals are

42
00:01:51,512 --> 00:01:53,746
spectacularly diverse.

43
00:01:53,747 --> 00:01:55,348
They not only survive,

44
00:01:55,349 --> 00:02:00,019
but thrive
in all kinds of environments.

45
00:02:00,020 --> 00:02:01,821
Mammals have basically
taken over the world.

46
00:02:01,822 --> 00:02:04,057
{\an8}There's mammals
all over the land.

47
00:02:04,058 --> 00:02:06,192
{\an8}There's mammals that fly
in the air.

48
00:02:06,193 --> 00:02:07,594
{\an8}There's mammals
that swim in the oceans.

49
00:02:07,595 --> 00:02:10,196
(squeaking)

50
00:02:10,197 --> 00:02:12,098
NARRATOR:
They range in size

51
00:02:12,099 --> 00:02:14,634
from tiny elephant shrews

52
00:02:14,635 --> 00:02:17,036
to gargantuan 200-ton whales.

53
00:02:17,037 --> 00:02:20,840
Yet all mammal species--
more than 6,000 of them--

54
00:02:20,841 --> 00:02:23,877
share many
of the same basic traits.

55
00:02:23,878 --> 00:02:25,578
{\an8}(cubs fussing)

56
00:02:25,579 --> 00:02:28,214
{\an8}They have hair or fur

57
00:02:28,215 --> 00:02:30,251
{\an8}and four chambers
in their hearts.

58
00:02:31,619 --> 00:02:34,187
{\an8}Mammals produce milk
for their young.

59
00:02:34,188 --> 00:02:37,190
{\an8}And they are all warm-blooded,

60
00:02:37,191 --> 00:02:41,060
{\an8}a trait that has long puzzled
scientists.

61
00:02:41,061 --> 00:02:42,862
The creatures
that mammals evolved from

62
00:02:42,863 --> 00:02:44,664
were cold-blooded,

63
00:02:44,665 --> 00:02:46,566
and so it's a really key thing

64
00:02:46,567 --> 00:02:47,667
in the history of mammals,

65
00:02:47,668 --> 00:02:49,702
figuring out
how and when and why

66
00:02:49,703 --> 00:02:53,072
our ancestors
changed their metabolism

67
00:02:53,073 --> 00:02:55,208
and started warming up
their bodies.

68
00:02:55,209 --> 00:02:56,976
{\an8}♪ ♪

69
00:02:56,977 --> 00:02:59,279
{\an8}NARRATOR:
So, where does
the mammal story begin?

70
00:02:59,280 --> 00:03:01,581
Where do we come from?

71
00:03:01,582 --> 00:03:03,884
♪ ♪

72
00:03:09,156 --> 00:03:13,326
{\an8}Rewind the clock
270 million years,

73
00:03:13,327 --> 00:03:17,463
{\an8}to a time
even before the dinosaurs.

74
00:03:17,464 --> 00:03:21,034
{\an8}Back then, our planet was home
not only

75
00:03:21,035 --> 00:03:24,203
{\an8}to the ancestors of the
dinosaurs and other reptiles,

76
00:03:24,204 --> 00:03:28,775
{\an8}but to another group,
also now long gone.

77
00:03:28,776 --> 00:03:32,612
Among them, creatures that would
one day give rise to mammals:

78
00:03:32,613 --> 00:03:35,248
the therapsids.

79
00:03:35,249 --> 00:03:38,718
Paleontologists have
known about them for decades,

80
00:03:38,719 --> 00:03:40,887
but in 2023,

81
00:03:40,888 --> 00:03:44,390
some of the oldest known remains
of these enigmatic animals

82
00:03:44,391 --> 00:03:45,692
were discovered in South Africa.

83
00:03:45,693 --> 00:03:50,930
♪ ♪

84
00:03:50,931 --> 00:03:53,266
{\an8}(translated): This skull
is 266 million years old,

85
00:03:53,267 --> 00:03:55,101
{\an8}which is really interesting,

86
00:03:55,102 --> 00:03:57,170
because it's one of
the oldest fossils we have.

87
00:03:57,171 --> 00:03:59,373
The snout is here,
in this direction.

88
00:04:00,708 --> 00:04:04,744
NARRATOR:
You can also clearly see
its teeth.

89
00:04:04,745 --> 00:04:07,914
This creature would have
been the size of a large dog,

90
00:04:07,915 --> 00:04:10,583
but with sprawling limbs
like a reptile

91
00:04:10,584 --> 00:04:13,486
and a cold-blooded metabolism.

92
00:04:13,487 --> 00:04:15,655
So what is it
that has scientists convinced

93
00:04:15,656 --> 00:04:17,457
it's not a reptile?

94
00:04:17,458 --> 00:04:19,559
(Benoît speaking French)

95
00:04:19,560 --> 00:04:21,127
(translated):
Here is the eye.

96
00:04:21,128 --> 00:04:23,162
And here, behind the eye,

97
00:04:23,163 --> 00:04:25,064
there's a pit called
the temporal fossa,

98
00:04:25,065 --> 00:04:26,199
which is an attachment point

99
00:04:26,200 --> 00:04:29,435
for the muscle
that closes the jaw.

100
00:04:29,436 --> 00:04:32,673
It's a defining characteristic
of therapsids.

101
00:04:33,874 --> 00:04:36,409
NARRATOR:
Dinosaurs, crocodiles,
and many reptiles

102
00:04:36,410 --> 00:04:39,979
have two of these pits,
called temporal fossae,

103
00:04:39,980 --> 00:04:41,615
on each side of their skulls.

104
00:04:42,583 --> 00:04:46,020
But therapsids have
just one pit behind each eye.

105
00:04:47,287 --> 00:04:48,554
It's the place
where the jaw muscles

106
00:04:48,555 --> 00:04:50,957
that control biting and chewing
are anchored.

107
00:04:50,958 --> 00:04:52,759
(growling)

108
00:04:52,760 --> 00:04:55,328
And the only other group
that has one pit behind each eye

109
00:04:55,329 --> 00:04:59,799
is our group: mammals.

110
00:04:59,800 --> 00:05:02,969
This anatomical similarity
was one of the first clues

111
00:05:02,970 --> 00:05:04,637
that led scientists to suspect

112
00:05:04,638 --> 00:05:06,873
that mammals and therapsids

113
00:05:06,874 --> 00:05:08,709
are part
of the same evolutionary line.

114
00:05:10,244 --> 00:05:12,712
But that's not
the only evidence.

115
00:05:12,713 --> 00:05:15,181
BENOÎT (translated):
You can see another
characteristic

116
00:05:15,182 --> 00:05:17,450
that distinguishes therapsids
from other animals,

117
00:05:17,451 --> 00:05:19,318
and that's their teeth.

118
00:05:19,319 --> 00:05:21,421
NARRATOR:
Therapsids have
specialized teeth,

119
00:05:21,422 --> 00:05:23,289
incisors for nipping

120
00:05:23,290 --> 00:05:25,191
and back teeth
known as "cheek teeth."

121
00:05:25,192 --> 00:05:27,026
The two groups of teeth

122
00:05:27,027 --> 00:05:29,162
are separated
by rather impressive canines.

123
00:05:29,163 --> 00:05:30,396
(ringing)

124
00:05:30,397 --> 00:05:32,965
Just like mammals today,

125
00:05:32,966 --> 00:05:35,268
including us humans.

126
00:05:35,269 --> 00:05:38,037
These shared features
helped convince scientists

127
00:05:38,038 --> 00:05:40,441
that therapsids
gave rise to mammals.

128
00:05:41,608 --> 00:05:43,276
BENOÎT (translated):
However,

129
00:05:43,277 --> 00:05:45,578
if you came across
any of them here today,

130
00:05:45,579 --> 00:05:46,679
you wouldn't realize

131
00:05:46,680 --> 00:05:48,047
that they were
the ancestors of mammals,

132
00:05:48,048 --> 00:05:50,183
because they looked a lot
like reptiles.

133
00:05:50,184 --> 00:05:52,085
Some were as big as rhinoceroses

134
00:05:52,086 --> 00:05:53,853
and others as small as mice.

135
00:05:53,854 --> 00:05:56,255
Some were carnivores,
others herbivores.

136
00:05:56,256 --> 00:05:58,792
There wasn't just one type
of therapsid, but lots.

137
00:06:01,462 --> 00:06:04,964
NARRATOR:
In fact, six main groups of
therapsids roamed ancient Earth,

138
00:06:04,965 --> 00:06:09,368
and each group included
many different species,

139
00:06:09,369 --> 00:06:13,106
including the 2023 fossil,

140
00:06:13,107 --> 00:06:15,875
which may be from a group
called the biarmosuchians,

141
00:06:15,876 --> 00:06:20,246
the most ancient and primitive
therapsids found so far.

142
00:06:20,247 --> 00:06:23,316
Many of the other groups
have more specialized traits,

143
00:06:23,317 --> 00:06:25,051
like dinocephalians,

144
00:06:25,052 --> 00:06:26,853
recognizable by their heads--

145
00:06:26,854 --> 00:06:28,689
thick skulls with bumps.

146
00:06:30,758 --> 00:06:32,125
And dicynodonts,

147
00:06:32,126 --> 00:06:34,828
which are distinguished
by a horny beak and tusks.

148
00:06:37,397 --> 00:06:41,434
Gorgonopsians are characterized
by their oversized canines,

149
00:06:41,435 --> 00:06:44,438
some even larger
than the teeth of a T. Rex.

150
00:06:47,474 --> 00:06:50,343
Therocephalians
had smaller jaws and teeth,

151
00:06:50,344 --> 00:06:52,579
but were more upright and agile.

152
00:06:54,548 --> 00:06:57,150
Finally, the cynodonts,

153
00:06:57,151 --> 00:06:59,453
many of which were small,
burrowing creatures.

154
00:07:00,788 --> 00:07:03,022
Altogether,
there were perhaps hundreds,

155
00:07:03,023 --> 00:07:04,924
if not thousands
of therapsid species

156
00:07:04,925 --> 00:07:06,893
among these
groups.

157
00:07:06,894 --> 00:07:08,661
They were
hugely varied

158
00:07:08,662 --> 00:07:10,129
in their
appearance and size,

159
00:07:10,130 --> 00:07:12,899
much like mammals
are today.

160
00:07:12,900 --> 00:07:14,500
One group
would lead

161
00:07:14,501 --> 00:07:15,902
to the emergence
of mammals on Earth

162
00:07:15,903 --> 00:07:19,005
225 million
years ago,

163
00:07:19,006 --> 00:07:22,475
{\an8}eventually evolving
and then likely passing down

164
00:07:22,476 --> 00:07:25,344
{\an8}the most iconic mammal features:

165
00:07:25,345 --> 00:07:27,380
{\an8}hair,

166
00:07:27,381 --> 00:07:30,383
{\an8}warm blood,

167
00:07:30,384 --> 00:07:34,320
{\an8}and lactation.

168
00:07:34,321 --> 00:07:37,957
{\an8}But which group was it?

169
00:07:37,958 --> 00:07:41,794
{\an8}♪ ♪

170
00:07:41,795 --> 00:07:46,465
Therapsid fossils have
been found on every continent,

171
00:07:46,466 --> 00:07:50,437
but one part of South Africa
is especially rich in clues.

172
00:07:52,673 --> 00:07:54,073
(Benoît speaking French)

173
00:07:54,074 --> 00:07:56,142
(translated):
The Karoo is one of the most

174
00:07:56,143 --> 00:07:57,877
important fossil sites
in the world.

175
00:07:57,878 --> 00:08:00,613
90% of fossils
found in these rocks

176
00:08:00,614 --> 00:08:04,083
are therapsids,
the ancestors of mammals.

177
00:08:04,084 --> 00:08:06,452
BRUCE RUBIDGE:
Many thousands of fossils

178
00:08:06,453 --> 00:08:08,788
have been discovered
in the Karoo,

179
00:08:08,789 --> 00:08:14,027
{\an8}and every field trip delivers
more fossils and new species.

180
00:08:16,330 --> 00:08:17,597
{\an8}NARRATOR:
This has been the case

181
00:08:17,598 --> 00:08:20,166
{\an8}since the first therapsid fossil
was found here

182
00:08:20,167 --> 00:08:21,935
in the 1830s.

183
00:08:24,004 --> 00:08:26,739
In the 1900s, during apartheid,

184
00:08:26,740 --> 00:08:30,844
access to dig sites was mostly
limited to white scientists.

185
00:08:32,179 --> 00:08:33,279
But today,

186
00:08:33,280 --> 00:08:35,181
the government
has opened up access

187
00:08:35,182 --> 00:08:36,783
and is supporting new projects.

188
00:08:37,918 --> 00:08:41,021
Now discoveries are on the rise.

189
00:08:43,624 --> 00:08:46,960
But why have so many therapsid
fossils been found here?

190
00:08:48,095 --> 00:08:49,161
What was this place like

191
00:08:49,162 --> 00:08:51,097
hundreds of millions
of years ago

192
00:08:51,098 --> 00:08:54,567
that allowed therapsids
not only to thrive,

193
00:08:54,568 --> 00:08:58,004
but to be preserved as stone?

194
00:08:58,005 --> 00:09:00,439
RUBIDGE:
Well, over here,
you can see these rocks

195
00:09:00,440 --> 00:09:02,441
and these ball structures,

196
00:09:02,442 --> 00:09:05,278
they form underwater.

197
00:09:05,279 --> 00:09:06,746
And accompanying
with these things,

198
00:09:06,747 --> 00:09:08,748
we find fossilized fishes

199
00:09:08,749 --> 00:09:11,183
and also fossilized wood,

200
00:09:11,184 --> 00:09:12,952
which didn't grow here,

201
00:09:12,953 --> 00:09:14,654
but it was transported in
by the rivers.

202
00:09:14,655 --> 00:09:18,325
We also find
lots of ripple marks.

203
00:09:19,626 --> 00:09:22,495
NARRATOR:
Fossil evidence suggests
a watery past.

204
00:09:22,496 --> 00:09:24,030
But to fully understand

205
00:09:24,031 --> 00:09:26,332
what the Karoo of the
therapsids' time looked like,

206
00:09:26,333 --> 00:09:29,702
we need to go back
300 million years,

207
00:09:29,703 --> 00:09:32,672
to a time when all
of today's continents

208
00:09:32,673 --> 00:09:35,041
existed as one landmass:

209
00:09:35,042 --> 00:09:37,476
Pangaea.

210
00:09:37,477 --> 00:09:39,445
What was to become South Africa

211
00:09:39,446 --> 00:09:41,914
was much closer
to the South Pole

212
00:09:41,915 --> 00:09:43,983
and under an ice cap.

213
00:09:43,984 --> 00:09:46,686
By 265 million years ago,

214
00:09:46,687 --> 00:09:49,021
the Earth was warming up.

215
00:09:49,022 --> 00:09:51,757
The ice that covered the Karoo
had melted,

216
00:09:51,758 --> 00:09:54,360
forming an inland sea.

217
00:09:54,361 --> 00:09:56,329
Over the next few million years,

218
00:09:56,330 --> 00:09:59,332
the Karoo Sea
filled with sediments.

219
00:09:59,333 --> 00:10:02,936
It nourished lush vegetation
that grew in the new wetlands.

220
00:10:04,504 --> 00:10:06,038
This was the environment

221
00:10:06,039 --> 00:10:09,142
where therapsids were first
preserved in the Karoo.

222
00:10:11,311 --> 00:10:12,845
The remains of the animals
that we are finding there,

223
00:10:12,846 --> 00:10:14,246
the fossils,

224
00:10:14,247 --> 00:10:17,317
were once living on the banks
of these rivers.

225
00:10:19,186 --> 00:10:22,555
NARRATOR:
But what was life like
for these ancient therapsids?

226
00:10:22,556 --> 00:10:26,225
Were any mammal-like traits
beginning to appear?

227
00:10:26,226 --> 00:10:28,194
♪ ♪

228
00:10:28,195 --> 00:10:30,196
One of the most exciting
discoveries

229
00:10:30,197 --> 00:10:32,365
was made in the mid-1980s

230
00:10:32,366 --> 00:10:36,236
by South African fossil
collector John Nyaphuli.

231
00:10:37,204 --> 00:10:40,272
John was my preparator

232
00:10:40,273 --> 00:10:43,275
at the National Museum in
Bloemfontein, where I worked.

233
00:10:43,276 --> 00:10:46,312
{\an8}He and I spent many, many years

234
00:10:46,313 --> 00:10:47,780
{\an8}out living in a tent,

235
00:10:47,781 --> 00:10:49,315
{\an8}collecting fossils.

236
00:10:49,316 --> 00:10:51,484
{\an8}It's not easy to find fossil.

237
00:10:51,485 --> 00:10:53,085
{\an8}But your eyes must be trained.

238
00:10:53,086 --> 00:10:55,855
{\an8}You can't find fossil anywhere.

239
00:10:55,856 --> 00:10:58,090
{\an8}You must go to the right areas,

240
00:10:58,091 --> 00:11:01,127
{\an8}because geology
must first tell you

241
00:11:01,128 --> 00:11:03,596
{\an8}that there was,
there's good place to trace.

242
00:11:03,597 --> 00:11:06,233
{\an8}And you must love the thing,
and then you can find them.

243
00:11:07,868 --> 00:11:11,237
{\an8}RUBIDGE:
In 1984, he said to me,

244
00:11:11,238 --> 00:11:13,239
{\an8}"I found some big bone
in the rock."

245
00:11:13,240 --> 00:11:16,742
{\an8}So I went to look at it,
and it was big bone.

246
00:11:16,743 --> 00:11:18,111
{\an8}It was sort of this size.

247
00:11:19,146 --> 00:11:21,514
{\an8}John started opening it up,

248
00:11:21,515 --> 00:11:23,682
{\an8}and we found that
by the middle of the day,

249
00:11:23,683 --> 00:11:25,918
we had a complete skull
of an animal.

250
00:11:25,919 --> 00:11:27,319
There were some teeth
sticking out.

251
00:11:27,320 --> 00:11:30,523
It went on into the ground,
and for several months,

252
00:11:30,524 --> 00:11:32,425
we started excavating it.

253
00:11:32,426 --> 00:11:35,995
(camera clicking)

254
00:11:35,996 --> 00:11:40,166
It took 23 years to expose
that skeleton fully.

255
00:11:40,167 --> 00:11:42,635
But it was a completely
new species of animal,

256
00:11:42,636 --> 00:11:44,403
it had never been found,

257
00:11:44,404 --> 00:11:46,907
and it was a very
primitive dinocephalian.

258
00:11:48,442 --> 00:11:51,744
This is the most complete
dinocephalian skeleton

259
00:11:51,745 --> 00:11:53,914
that's yet been found
in the world.

260
00:11:56,583 --> 00:12:00,619
NARRATOR:
Dinocephalians were a group
of early therapsids.

261
00:12:00,620 --> 00:12:04,423
This remarkable specimen
was more than nine feet long.

262
00:12:04,424 --> 00:12:06,392
The name "dinocephalian"

263
00:12:06,393 --> 00:12:10,029
comes from the Greek
for "terrible heads,"

264
00:12:10,030 --> 00:12:12,698
because they had
especially thick skulls--

265
00:12:12,699 --> 00:12:17,203
in some areas, more than
four inches of solid bone.

266
00:12:17,204 --> 00:12:21,240
But what was all that extra
skull thickness used for?

267
00:12:21,241 --> 00:12:25,044
♪ ♪

268
00:12:25,045 --> 00:12:28,013
In the French Alps,
scientists are looking for clues

269
00:12:28,014 --> 00:12:31,284
with a powerful X-ray source
called a synchrotron.

270
00:12:32,686 --> 00:12:36,322
Here, in a ring larger
than seven soccer fields,

271
00:12:36,323 --> 00:12:39,459
electrons circulate
at almost the speed of light.

272
00:12:42,929 --> 00:12:44,830
VINCENT FERNANDEZ (translated):
The synchrotron radiation
is so intense

273
00:12:44,831 --> 00:12:48,467
that it produces 10,000 billion
times more intense X-rays

274
00:12:48,468 --> 00:12:50,936
than a hospital
or laboratory scanner.

275
00:12:50,937 --> 00:12:53,339
With this very intense signal,
we're able to see

276
00:12:53,340 --> 00:12:54,874
through the thickness of the
fossil

277
00:12:54,875 --> 00:12:56,976
and produce beautiful images.

278
00:12:56,977 --> 00:13:00,179
♪ ♪

279
00:13:00,180 --> 00:13:02,715
NARRATOR:
Paleontologist Vincent Fernandez

280
00:13:02,716 --> 00:13:04,984
is scanning another
dinocephalian skull

281
00:13:04,985 --> 00:13:06,486
found in the Karoo.

282
00:13:08,421 --> 00:13:10,756
His colleague, paleontologist
Julien Benoît,

283
00:13:10,757 --> 00:13:13,592
is doing the analysis.

284
00:13:13,593 --> 00:13:16,128
BENOÎT:
Here you can see,
that's the brain cavity.

285
00:13:16,129 --> 00:13:20,132
And it's very small compared
to the large size of the skull,

286
00:13:20,133 --> 00:13:23,335
and in particular, you have
that thickness of bone.

287
00:13:23,336 --> 00:13:25,070
{\an8}This is all bone.
Wow.

288
00:13:25,071 --> 00:13:26,539
This is not rock.

289
00:13:26,540 --> 00:13:28,675
NARRATOR:
Why is the bone so thick here?

290
00:13:30,343 --> 00:13:32,912
Back at the University
of the Witwatersrand,

291
00:13:32,913 --> 00:13:35,514
Julien uses
the synchrotron scans

292
00:13:35,515 --> 00:13:37,983
to reconstruct a 3-D model

293
00:13:37,984 --> 00:13:40,253
of the organs that were
once inside the skull.

294
00:13:42,055 --> 00:13:44,256
(translated):
You can see the brain in green.

295
00:13:44,257 --> 00:13:45,824
What's really interesting
about this scan

296
00:13:45,825 --> 00:13:48,427
is that we can also
very clearly see

297
00:13:48,428 --> 00:13:50,729
this animal's inner ear.

298
00:13:50,730 --> 00:13:52,598
NARRATOR:
It's shown here in purple.

299
00:13:52,599 --> 00:13:54,667
(Benoît speaking French)

300
00:13:54,668 --> 00:13:55,968
(translated):
This organ is used for hearing,

301
00:13:55,969 --> 00:13:58,337
but also for balance,

302
00:13:58,338 --> 00:14:01,941
{\an8}particularly these
three semicircular canals.

303
00:14:01,942 --> 00:14:04,443
{\an8}One here, a second here,

304
00:14:04,444 --> 00:14:05,611
{\an8}and the third.

305
00:14:05,612 --> 00:14:09,081
{\an8}Let me move the image--
it's here.

306
00:14:09,082 --> 00:14:12,418
NARRATOR:
The orientation of these
ear canals in the skull

307
00:14:12,419 --> 00:14:15,054
suggests
that this dinocephalian's head

308
00:14:15,055 --> 00:14:16,722
would usually point down,

309
00:14:16,723 --> 00:14:20,359
a bit like that of a goat
or a sheep today.

310
00:14:20,360 --> 00:14:21,727
(goat bleats)

311
00:14:21,728 --> 00:14:23,529
And if mammals like these
are any guide,

312
00:14:23,530 --> 00:14:26,932
that might mean that
the dinocephalians also engaged

313
00:14:26,933 --> 00:14:29,002
in social behaviors
like ramming.

314
00:14:33,607 --> 00:14:37,576
{\an8}♪ ♪

315
00:14:37,577 --> 00:14:40,446
{\an8}As the sun rose
on ancestral Earth,

316
00:14:40,447 --> 00:14:43,315
{\an8}dinocephalians awoke.

317
00:14:43,316 --> 00:14:46,452
{\an8}(animals grunting)

318
00:14:46,453 --> 00:14:48,722
{\an8}(bellows)

319
00:14:50,223 --> 00:14:53,459
{\an8}Living in a swampy landscape
where food was abundant,

320
00:14:53,460 --> 00:14:56,195
{\an8}they thrived,

321
00:14:56,196 --> 00:14:58,097
{\an8}great herds of them
perhaps living together

322
00:14:58,098 --> 00:14:59,398
{\an8}and interacting as a group.

323
00:14:59,399 --> 00:15:01,667
{\an8}(animals grunting)

324
00:15:01,668 --> 00:15:04,103
{\an8}With behaviors similar
to some of today's mammals,

325
00:15:04,104 --> 00:15:06,538
{\an8}could these dinocephalians

326
00:15:06,539 --> 00:15:08,440
{\an8}have been the mammal ancestors?

327
00:15:08,441 --> 00:15:12,812
{\an8}♪ ♪

328
00:15:14,247 --> 00:15:16,115
{\an8}Fossils found in the Karoo
reveal

329
00:15:16,116 --> 00:15:18,484
{\an8}that 265 million years ago--

330
00:15:18,485 --> 00:15:20,552
{\an8}nearly 40 million years before

331
00:15:20,553 --> 00:15:21,987
{\an8}the appearance of mammals--

332
00:15:21,988 --> 00:15:23,589
{\an8}five therapsid groups

333
00:15:23,590 --> 00:15:25,457
{\an8}were living here.

334
00:15:25,458 --> 00:15:27,026
{\an8}And the dinocephalians

335
00:15:27,027 --> 00:15:29,595
{\an8}were likely the most dominant.

336
00:15:29,596 --> 00:15:33,198
♪ ♪

337
00:15:33,199 --> 00:15:36,902
This is the skull
of Anteosaurus,

338
00:15:36,903 --> 00:15:40,739
a particularly menacing type
of dinocephalian.

339
00:15:40,740 --> 00:15:42,574
BENOÎT:
The top of the snout is there,

340
00:15:42,575 --> 00:15:44,376
and the back of the skull
is there.

341
00:15:44,377 --> 00:15:45,611
And this was a therapsid,

342
00:15:45,612 --> 00:15:49,381
because you can see
this temporal fenestra here.

343
00:15:49,382 --> 00:15:51,216
It's very big,

344
00:15:51,217 --> 00:15:54,053
so the jaw muscle must have
been incredibly powerful.

345
00:15:54,054 --> 00:15:56,455
And it is a dinocephalian

346
00:15:56,456 --> 00:15:58,991
because of the thickness
of the bones

347
00:15:58,992 --> 00:16:01,894
that make up
the whole skull.

348
00:16:01,895 --> 00:16:03,295
NARRATOR:
But it's also very different

349
00:16:03,296 --> 00:16:06,465
from the other species
of thick-skulled dinocephalians

350
00:16:06,466 --> 00:16:07,767
Julien studies.

351
00:16:09,369 --> 00:16:12,604
{\an8}BENOÎT:
That canine here
is beautifully recurved,

352
00:16:12,605 --> 00:16:15,074
{\an8}which is really a signature
of carnivorous animals.

353
00:16:15,075 --> 00:16:18,877
NARRATOR:
These Anteosaurus
were large creatures,

354
00:16:18,878 --> 00:16:20,179
likely predators,

355
00:16:20,180 --> 00:16:24,149
some 20 feet long
when fully grown.

356
00:16:24,150 --> 00:16:25,984
But as successful
as they might have been,

357
00:16:25,985 --> 00:16:29,055
the dinocephalians weren't
the only therapsid group.

358
00:16:31,091 --> 00:16:34,360
They were just one part
of a complex ecosystem

359
00:16:34,361 --> 00:16:37,062
that included
other therapsid groups.

360
00:16:37,063 --> 00:16:39,098
(animals grunting)

361
00:16:39,099 --> 00:16:41,500
Based on fossils
found in the Karoo,

362
00:16:41,501 --> 00:16:43,502
we know that many species

363
00:16:43,503 --> 00:16:45,237
from all five groups
of therapsids

364
00:16:45,238 --> 00:16:47,206
existed alongside each other.

365
00:16:47,207 --> 00:16:50,309
♪ ♪

366
00:16:50,310 --> 00:16:51,744
Like dicynodonts.

367
00:16:51,745 --> 00:16:53,612
Equipped with unique beaks,

368
00:16:53,613 --> 00:16:57,049
these therapsids had their own
specialized feeding habits,

369
00:16:57,050 --> 00:17:01,020
able to efficiently tear
and clip plant material.

370
00:17:02,689 --> 00:17:04,790
{\an8}(growling)

371
00:17:04,791 --> 00:17:06,492
{\an8}Carnivorous therapsids,

372
00:17:06,493 --> 00:17:08,928
{\an8}such as gorgonopsians,
would have been a threat.

373
00:17:12,165 --> 00:17:14,600
(roaring)

374
00:17:14,601 --> 00:17:18,504
But the most fearsome
was still the Anteosaurus.

375
00:17:18,505 --> 00:17:22,274
This dinocephalian beast
was a true apex predator

376
00:17:22,275 --> 00:17:24,843
in the ancient
Middle Permian Karoo.

377
00:17:24,844 --> 00:17:29,182
♪ ♪

378
00:17:31,317 --> 00:17:34,753
Therapsids lived here
about 265 million

379
00:17:34,754 --> 00:17:38,157
to 125 million years ago.

380
00:17:38,158 --> 00:17:40,659
Within that time, they came up

381
00:17:40,660 --> 00:17:42,361
against more than one
global catastrophe

382
00:17:42,362 --> 00:17:45,664
that threatened to wipe out
nearly all life on Earth.

383
00:17:45,665 --> 00:17:49,168
And today, the Karoo
still bears the scars.

384
00:17:49,169 --> 00:17:53,672
♪ ♪

385
00:17:53,673 --> 00:17:55,340
For more than 15 years,

386
00:17:55,341 --> 00:17:57,943
paleontologist Mike Day
and his team have been

387
00:17:57,944 --> 00:18:01,281
accumulating evidence of
these large-scale extinctions.

388
00:18:03,483 --> 00:18:04,683
{\an8}DAY:
If you were to go
a little further south,

389
00:18:04,684 --> 00:18:06,418
{\an8}into slightly older rocks,

390
00:18:06,419 --> 00:18:08,787
{\an8}you'd find all those
typical Middle Permian faunas:

391
00:18:08,788 --> 00:18:10,722
the large dinocephalians,

392
00:18:10,723 --> 00:18:13,091
the big therocephalians,
and lots of dicynodonts.

393
00:18:13,092 --> 00:18:16,895
But by the time you get to
this sandstone behind us here,

394
00:18:16,896 --> 00:18:19,865
they've all gone extinct.

395
00:18:19,866 --> 00:18:22,534
NARRATOR:
Victims of a mass extinction
event

396
00:18:22,535 --> 00:18:24,771
called the Permian Extinction.

397
00:18:26,973 --> 00:18:29,341
Fossil evidence suggests

398
00:18:29,342 --> 00:18:30,876
that for as long
as eight million years,

399
00:18:30,877 --> 00:18:35,215
life on Earth was
under tremendous pressure.

400
00:18:38,318 --> 00:18:40,652
And as more and more fossils
have been found

401
00:18:40,653 --> 00:18:42,855
and plotted
along the rock record,

402
00:18:42,856 --> 00:18:44,356
scientists now believe

403
00:18:44,357 --> 00:18:46,859
that within
these eight million years,

404
00:18:46,860 --> 00:18:49,963
there were actually
two distinct extinction events.

405
00:18:54,100 --> 00:18:55,734
DAY:
Now, both of these
mass extinctions

406
00:18:55,735 --> 00:18:57,903
affected therapsids badly,

407
00:18:57,904 --> 00:18:59,238
but there were survivors.

408
00:18:59,239 --> 00:19:01,940
And those survivors include
the ancestors of mammals.

409
00:19:01,941 --> 00:19:05,310
NARRATOR:
But what caused the first
of these huge events,

410
00:19:05,311 --> 00:19:09,882
a global catastrophe known
as the Capitanian crisis?

411
00:19:09,883 --> 00:19:12,918
In terms of a smoking gun
here in the Karoo,

412
00:19:12,919 --> 00:19:14,486
we haven't really found
any good evidence

413
00:19:14,487 --> 00:19:16,321
for what caused
this mass extinction here.

414
00:19:16,322 --> 00:19:18,390
We do know
that in Southeast China,

415
00:19:18,391 --> 00:19:20,359
there was huge outpourings
of lava

416
00:19:20,360 --> 00:19:21,960
at about the same time,

417
00:19:21,961 --> 00:19:24,930
so it's very likely
that that had something to do

418
00:19:24,931 --> 00:19:26,865
with the Capitanian extinction
here in the Karoo.

419
00:19:26,866 --> 00:19:29,735
♪ ♪

420
00:19:29,736 --> 00:19:32,204
NARRATOR:
Around 260 million years ago,

421
00:19:32,205 --> 00:19:34,239
far away from the Karoo,

422
00:19:34,240 --> 00:19:36,074
at the other end of Pangaea,

423
00:19:36,075 --> 00:19:39,678
Earth's surface was volatile.

424
00:19:39,679 --> 00:19:43,749
In what was to become China,
immense molten lava flows

425
00:19:43,750 --> 00:19:47,419
spread across
around 100,000 square miles,

426
00:19:47,420 --> 00:19:49,087
releasing vast quantities

427
00:19:49,088 --> 00:19:51,456
of carbon dioxide, methane,
and sulfur

428
00:19:51,457 --> 00:19:52,725
into the atmosphere.

429
00:19:54,727 --> 00:19:57,963
The oceans became acidified
and depleted of oxygen,

430
00:19:57,964 --> 00:20:00,265
and the climate changed.

431
00:20:00,266 --> 00:20:01,900
This is most likely the event

432
00:20:01,901 --> 00:20:04,470
that caused
the Capitanian crisis.

433
00:20:06,839 --> 00:20:07,974
(grunting)

434
00:20:08,942 --> 00:20:11,476
It was disastrous for life,

435
00:20:11,477 --> 00:20:13,979
particularly for large animals.

436
00:20:13,980 --> 00:20:15,447
But we know that at least

437
00:20:15,448 --> 00:20:16,982
some therapsids survived.

438
00:20:16,983 --> 00:20:19,451
Otherwise, we wouldn't be here.

439
00:20:19,452 --> 00:20:21,119
But which ones?

440
00:20:21,120 --> 00:20:22,655
And how?

441
00:20:25,525 --> 00:20:26,892
During the crisis,

442
00:20:26,893 --> 00:20:29,094
environmental disturbances
like acid rain

443
00:20:29,095 --> 00:20:30,996
and a rapidly changing climate

444
00:20:30,997 --> 00:20:34,366
likely ravaged the vegetation,

445
00:20:34,367 --> 00:20:35,867
causing the extinction

446
00:20:35,868 --> 00:20:37,971
of the large plant-eating
dinocephalians.

447
00:20:40,173 --> 00:20:41,406
Their carnivorous cousins

448
00:20:41,407 --> 00:20:43,442
eventually suffered
the same fate.

449
00:20:43,443 --> 00:20:44,643
(animal moaning)

450
00:20:44,644 --> 00:20:47,779
Earth's first giants,
the dinocephalians,

451
00:20:47,780 --> 00:20:50,950
did not survive to become
our direct ancestors.

452
00:20:52,719 --> 00:20:54,486
But what about
the other four groups

453
00:20:54,487 --> 00:20:56,955
alive in the Karoo at this time,

454
00:20:56,956 --> 00:21:00,225
the gorgonopsians,
with their huge teeth,

455
00:21:00,226 --> 00:21:02,494
the upright and agile
therocephalians,

456
00:21:02,495 --> 00:21:05,530
the beaked dicynodonts,

457
00:21:05,531 --> 00:21:08,166
and the primitive
biarmosuchians?

458
00:21:08,167 --> 00:21:10,203
Did the rest of them make it?

459
00:21:11,270 --> 00:21:14,973
♪ ♪

460
00:21:14,974 --> 00:21:18,177
The Karoo fossil record
reveals the survivors.

461
00:21:20,580 --> 00:21:22,948
This is the Rubidge Collection
of Fossils.

462
00:21:22,949 --> 00:21:25,183
It was amassed largely through
the enthusiasm

463
00:21:25,184 --> 00:21:29,054
of my grandfather from
the 1930s.

464
00:21:29,055 --> 00:21:31,890
NARRATOR:
These fossils were collected
by Sidney Rubidge

465
00:21:31,891 --> 00:21:34,593
from sediment
above a volcanic ash layer

466
00:21:34,594 --> 00:21:37,362
dated to the end
of the Capitanian crisis.

467
00:21:37,363 --> 00:21:40,165
They show that in the Karoo,

468
00:21:40,166 --> 00:21:43,835
all therapsid groups other
than the dinocephalians made it,

469
00:21:43,836 --> 00:21:47,139
but only some of
the smallest species of each.

470
00:21:47,140 --> 00:21:50,043
The largest were lost.

471
00:21:51,611 --> 00:21:54,913
The question then becomes,
which of these remaining groups

472
00:21:54,914 --> 00:21:57,582
would give rise
to the mammal line?

473
00:21:57,583 --> 00:21:59,618
One of the most
interesting fossils

474
00:21:59,619 --> 00:22:01,119
in the Rubidge Collection

475
00:22:01,120 --> 00:22:02,889
is a member of
the gorgonopsian group.

476
00:22:04,724 --> 00:22:08,627
Gorgonopsians were the
apex predators of the time.

477
00:22:08,628 --> 00:22:11,196
NARRATOR:
With the dinocephalians gone,

478
00:22:11,197 --> 00:22:13,565
they became
top of the food chain,

479
00:22:13,566 --> 00:22:18,036
and the new species that evolved
were much larger in size.

480
00:22:18,037 --> 00:22:19,972
And this one is called
Rubidgea atrox.

481
00:22:21,240 --> 00:22:23,008
These large gorgonopsians

482
00:22:23,009 --> 00:22:25,077
might have been
three-and-a-half meters long.

483
00:22:25,078 --> 00:22:27,612
They probably had
a more leathery skin,

484
00:22:27,613 --> 00:22:29,314
something like a rhino
or an elephant.

485
00:22:29,315 --> 00:22:33,919
They're characterized by
having very large canine teeth

486
00:22:33,920 --> 00:22:36,923
{\an8}and large incisors
for flesh eating.

487
00:22:38,257 --> 00:22:40,959
{\an8}NARRATOR:
Only small species
of gorgonopsians

488
00:22:40,960 --> 00:22:43,729
survived the Capitanian crisis,

489
00:22:43,730 --> 00:22:45,764
but the Rubidge Collection shows

490
00:22:45,765 --> 00:22:48,600
that as the ecosystem recovered
and food returned,

491
00:22:48,601 --> 00:22:53,872
these small gorgonopsians
not only survived, but thrived.

492
00:22:53,873 --> 00:22:58,010
Over time, they evolved to be
the size of modern-day bears.

493
00:22:59,445 --> 00:23:01,580
And in the fossil record,
there is evidence

494
00:23:01,581 --> 00:23:04,349
that some new traits
might have been developing.

495
00:23:04,350 --> 00:23:07,452
♪ ♪

496
00:23:07,453 --> 00:23:11,356
A gorgonopsian fossil
originally found in the 1940s

497
00:23:11,357 --> 00:23:12,691
recently provided new clues

498
00:23:12,692 --> 00:23:14,761
to how they might have lived.

499
00:23:16,262 --> 00:23:18,597
{\an8}Inside this skull
are the remains

500
00:23:18,598 --> 00:23:20,532
{\an8}of an encounter
with another animal.

501
00:23:20,533 --> 00:23:23,835
BENOÎT (translated):
Here is a tooth stuck
in its snout,

502
00:23:23,836 --> 00:23:25,971
and this tooth
isn't just any tooth,

503
00:23:25,972 --> 00:23:28,039
{\an8}it's the tooth
of another gorgonopsian.

504
00:23:28,040 --> 00:23:29,241
{\an8}The same species.

505
00:23:29,242 --> 00:23:30,275
{\an8}And you can even see

506
00:23:30,276 --> 00:23:31,910
{\an8}that it survived the fight,

507
00:23:31,911 --> 00:23:33,279
{\an8}because the wound
around the tooth has healed.

508
00:23:35,181 --> 00:23:36,648
NARRATOR:
For Julien,

509
00:23:36,649 --> 00:23:40,118
this is a sign of how these
animals may have interacted.

510
00:23:40,119 --> 00:23:42,354
(translated):
These animals fought
among themselves,

511
00:23:42,355 --> 00:23:45,290
biting each other on the snout,

512
00:23:45,291 --> 00:23:46,725
exactly as mammals do today

513
00:23:46,726 --> 00:23:49,928
to determine dominance
within groups

514
00:23:49,929 --> 00:23:52,298
and also to find mates
and claim territories.

515
00:23:54,200 --> 00:23:55,700
NARRATOR:
Until this discovery,

516
00:23:55,701 --> 00:23:57,869
the teeth
of carnivorous therapsids

517
00:23:57,870 --> 00:24:00,072
had been considered
solely hunting weapons.

518
00:24:01,941 --> 00:24:04,976
And although not direct evidence
of mammal ancestry,

519
00:24:04,977 --> 00:24:07,045
using them
for more social interactions,

520
00:24:07,046 --> 00:24:08,847
like competition,

521
00:24:08,848 --> 00:24:10,982
is certainly
a characteristic seen

522
00:24:10,983 --> 00:24:12,984
{\an8}in many mammals alive today.

523
00:24:12,985 --> 00:24:14,186
{\an8}(badgers growling)

524
00:24:14,187 --> 00:24:15,754
But the gorgonopsians

525
00:24:15,755 --> 00:24:18,957
weren't the only ones
developing new behaviors.

526
00:24:18,958 --> 00:24:21,026
The dicynodonts were adapting

527
00:24:21,027 --> 00:24:23,162
in the post-extinction world,
as well.

528
00:24:24,897 --> 00:24:28,033
Perhaps the most varied
of the therapsids,

529
00:24:28,034 --> 00:24:29,968
they came in a wide range
of sizes,

530
00:24:29,969 --> 00:24:32,405
some as small as guinea pigs.

531
00:24:35,041 --> 00:24:38,176
The only known therapsid group
with beaks,

532
00:24:38,177 --> 00:24:40,378
some also had tusks.

533
00:24:40,379 --> 00:24:42,547
(roaring)

534
00:24:42,548 --> 00:24:46,451
What was it about the dicynodont
group that helped it survive?

535
00:24:46,452 --> 00:24:51,089
{\an8}♪ ♪

536
00:24:51,090 --> 00:24:54,460
A fossil in South Africa
might hold the answer.

537
00:24:56,095 --> 00:24:59,131
♪ ♪

538
00:25:01,200 --> 00:25:03,802
{\an8}Here we see a new behavior
in the late Permian,

539
00:25:03,803 --> 00:25:06,671
{\an8}where animals were starting
to burrow underground

540
00:25:06,672 --> 00:25:09,441
{\an8}and create these
really interesting spirals

541
00:25:09,442 --> 00:25:11,543
with a chamber underneath,
where they would live.

542
00:25:11,544 --> 00:25:14,480
We can see it here because it's
actually preserved as a cast.

543
00:25:15,948 --> 00:25:18,149
NARRATOR:
This cast is natural.

544
00:25:18,150 --> 00:25:20,785
A flood poured sediment
into a hollow burrow,

545
00:25:20,786 --> 00:25:22,854
which hardened into rock
over time.

546
00:25:22,855 --> 00:25:25,490
But what were these burrows
used for?

547
00:25:25,491 --> 00:25:27,860
How were they an advantage?

548
00:25:30,496 --> 00:25:32,764
{\an8}To see
through this mass of rock,

549
00:25:32,765 --> 00:25:34,032
{\an8}a dicynodont burrow cast

550
00:25:34,033 --> 00:25:36,067
was sent to the synchrotron.

551
00:25:36,068 --> 00:25:38,203
And hidden inside,

552
00:25:38,204 --> 00:25:39,871
fossilized remains.

553
00:25:39,872 --> 00:25:41,773
This is the burrow that was
discovered

554
00:25:41,774 --> 00:25:43,441
with the dicynodont.

555
00:25:43,442 --> 00:25:47,546
NARRATOR:
Removing the rock reveals
a spectacular find.

556
00:25:48,614 --> 00:25:51,316
FERNANDEZ:
We have the adult dicynodont.

557
00:25:51,317 --> 00:25:53,385
We can see, like,

558
00:25:53,386 --> 00:25:56,321
right in the middle,
this big eye socket

559
00:25:56,322 --> 00:25:57,555
and teeth in front.

560
00:25:57,556 --> 00:25:59,124
The beak would be there,
as well.

561
00:25:59,125 --> 00:26:02,193
NARRATOR:
That's not all
this ancient burrow was hiding.

562
00:26:02,194 --> 00:26:05,864
There was another,
more unexpected find.

563
00:26:05,865 --> 00:26:07,198
It's like it's a,

564
00:26:07,199 --> 00:26:08,801
it's a baby version
of the same species.

565
00:26:10,303 --> 00:26:12,370
So basically,
it's telling us

566
00:26:12,371 --> 00:26:14,539
that dicynodont,
they were using burrows

567
00:26:14,540 --> 00:26:17,475
kind of as nurseries
to take care of their babies.

568
00:26:17,476 --> 00:26:19,010
{\an8}(cubs fussing)

569
00:26:19,011 --> 00:26:20,378
{\an8}NARRATOR:
It appears that a semblance

570
00:26:20,379 --> 00:26:22,781
{\an8}of today's mammalian
parent-child bond

571
00:26:22,782 --> 00:26:26,885
{\an8}may have existed
260 million years ago,

572
00:26:26,886 --> 00:26:29,889
but it's an idea that scientists
are still exploring.

573
00:26:31,090 --> 00:26:32,757
What we do know
is that these burrows

574
00:26:32,758 --> 00:26:38,263
allowed dicynodonts to survive
tough post-crisis conditions.

575
00:26:38,264 --> 00:26:39,831
BROWNING:
That kind of group sharing
behavior

576
00:26:39,832 --> 00:26:42,434
has a lot
of different advantages.

577
00:26:42,435 --> 00:26:44,569
If you're in a burrow,
you're protected from predators.

578
00:26:44,570 --> 00:26:46,671
You're protected from the sun.

579
00:26:46,672 --> 00:26:48,807
It's, it's pretty good to be
in a burrow

580
00:26:48,808 --> 00:26:50,810
if it's hot outside--
hot and dry.

581
00:26:52,278 --> 00:26:55,414
NARRATOR:
But how well did the other
therapsid groups fare?

582
00:27:00,152 --> 00:27:02,120
{\an8}After the Capitanian crisis,

583
00:27:02,121 --> 00:27:05,290
{\an8}not all therapsid groups
had the same fate.

584
00:27:05,291 --> 00:27:08,260
{\an8}The dinocephalians
disappeared completely.

585
00:27:10,596 --> 00:27:13,399
{\an8}The gorgonopsians emerged
as the apex predators.

586
00:27:16,502 --> 00:27:18,236
{\an8}As for the therocephalians,

587
00:27:18,237 --> 00:27:21,706
{\an8}they took second place
to their larger cousins.

588
00:27:21,707 --> 00:27:23,541
The biarmosuchians

589
00:27:23,542 --> 00:27:24,676
were still
holding on,

590
00:27:24,677 --> 00:27:27,345
but also remained
the most primitive.

591
00:27:27,346 --> 00:27:29,080
It was
the dicynodonts

592
00:27:29,081 --> 00:27:30,115
who adapted best

593
00:27:30,116 --> 00:27:31,549
to the changing
environments.

594
00:27:31,550 --> 00:27:33,385
But as some groups
struggled,

595
00:27:33,386 --> 00:27:35,554
the picture grew
more complicated.

596
00:27:36,889 --> 00:27:38,456
A new group
emerged

597
00:27:38,457 --> 00:27:40,458
in a post-crisis therapsid boom,

598
00:27:40,459 --> 00:27:43,361
taking the number
of existing therapsid groups

599
00:27:43,362 --> 00:27:45,997
back up to five:

600
00:27:45,998 --> 00:27:47,166
the cynodonts.

601
00:27:48,768 --> 00:27:51,870
They shared a common ancestor
with the therocephalians,

602
00:27:51,871 --> 00:27:53,371
and it's possible that they were

603
00:27:53,372 --> 00:27:55,975
actually just a sub-group
of therocephalians themselves.

604
00:27:57,209 --> 00:27:59,010
{\an8}But one thing
is certain:

605
00:27:59,011 --> 00:28:00,311
{\an8}one of
the secrets

606
00:28:00,312 --> 00:28:01,646
{\an8}to their success

607
00:28:01,647 --> 00:28:03,015
{\an8}was their size.

608
00:28:04,483 --> 00:28:06,885
{\an8}Cynodonts generally were
quite small.

609
00:28:06,886 --> 00:28:09,255
{\an8}You could hold most of them
in your arms.

610
00:28:10,256 --> 00:28:11,756
{\an8}(snarling)

611
00:28:11,757 --> 00:28:14,092
{\an8}NARRATOR:
They also had relatively
larger brains

612
00:28:14,093 --> 00:28:15,361
{\an8}and more specialized teeth.

613
00:28:17,263 --> 00:28:19,664
{\an8}With the Karoo ecosystem
having recovered

614
00:28:19,665 --> 00:28:21,032
{\an8}from the Capitanian crisis,

615
00:28:21,033 --> 00:28:23,736
{\an8}the five groups of therapsids
stabilized.

616
00:28:25,371 --> 00:28:29,508
{\an8}Cynodonts thrived, feeding off
insects and other small animals.

617
00:28:30,476 --> 00:28:33,778
{\an8}Meanwhile, dicynodonts continued
with their plant-eating diets

618
00:28:33,779 --> 00:28:37,348
{\an8}and still used burrows
as their homes.

619
00:28:37,349 --> 00:28:39,885
{\an8}But this wasn't
always an advantage.

620
00:28:41,620 --> 00:28:45,190
Dicynodonts were also the prey
of choice for therocephalians.

621
00:28:45,191 --> 00:28:48,326
These larger predators
were perhaps able to hunt down

622
00:28:48,327 --> 00:28:50,562
entire dicynodont families.

623
00:28:50,563 --> 00:28:53,932
Even so, gorgonopsians remained

624
00:28:53,933 --> 00:28:55,500
the apex predators.

625
00:28:55,501 --> 00:28:56,835
(roaring)

626
00:28:56,836 --> 00:28:58,403
But, at the end
of the Permian period,

627
00:28:58,404 --> 00:29:00,572
another crisis.

628
00:29:00,573 --> 00:29:04,375
In the rock layers of the Karoo
dating to the period

629
00:29:04,376 --> 00:29:06,544
after 252 million years ago,

630
00:29:06,545 --> 00:29:10,281
most big dicynodonts
and gorgonopsians disappear,

631
00:29:10,282 --> 00:29:13,384
signaling
another extinction crisis.

632
00:29:13,385 --> 00:29:15,653
(roaring)

633
00:29:15,654 --> 00:29:18,490
Was it something local
to the Karoo

634
00:29:18,491 --> 00:29:20,359
or more global?

635
00:29:21,727 --> 00:29:23,495
Since the 1990s,

636
00:29:23,496 --> 00:29:26,197
scientists have suspected
that the Siberian Traps,

637
00:29:26,198 --> 00:29:29,968
enormous volcanic eruptions
in what is today's Russia,

638
00:29:29,969 --> 00:29:32,204
were responsible.

639
00:29:33,839 --> 00:29:36,808
In 2023, an international team
of scientists

640
00:29:36,809 --> 00:29:39,078
published a project
testing the idea.

641
00:29:41,514 --> 00:29:44,482
JENNIFER BOTHA:
When scientists studied
the rocks in Siberia,

642
00:29:44,483 --> 00:29:45,783
they found that there was

643
00:29:45,784 --> 00:29:47,118
an increase in mercury

644
00:29:47,119 --> 00:29:48,820
in the rocks that they sampled.

645
00:29:48,821 --> 00:29:50,555
So there was a mercury spike,

646
00:29:50,556 --> 00:29:52,357
and they found this associated

647
00:29:52,358 --> 00:29:54,226
with those volcanic eruptions.

648
00:29:56,028 --> 00:29:59,731
NARRATOR:
Mercury is often associated
with volcanoes.

649
00:29:59,732 --> 00:30:02,400
As a volcano erupts,
spewing out lava,

650
00:30:02,401 --> 00:30:06,371
it also releases mercury vapor
into the atmosphere.

651
00:30:06,372 --> 00:30:09,107
This vapor can be transported
across continents

652
00:30:09,108 --> 00:30:10,742
by currents and winds.

653
00:30:10,743 --> 00:30:14,312
(current churning)

654
00:30:14,313 --> 00:30:15,847
But we did not know

655
00:30:15,848 --> 00:30:19,151
whether we had such a spike in
the Karoo Basin of South Africa.

656
00:30:20,753 --> 00:30:23,421
NARRATOR:
If found, that spike
could be evidence

657
00:30:23,422 --> 00:30:25,356
that these Siberian eruptions

658
00:30:25,357 --> 00:30:26,891
{\an8}were responsible
for the climate changes

659
00:30:26,892 --> 00:30:30,361
{\an8}that caused the extinction event
seen in the Karoo.

660
00:30:30,362 --> 00:30:33,998
BOTHA:
So our team went to the field
and we collected samples,

661
00:30:33,999 --> 00:30:35,867
and we ran the analyses,

662
00:30:35,868 --> 00:30:37,402
and we found that indeed,

663
00:30:37,403 --> 00:30:40,439
we are finding a mercury spike
in South Africa.

664
00:30:42,608 --> 00:30:45,076
NARRATOR:
The therapsid extinctions
in the Karoo

665
00:30:45,077 --> 00:30:47,245
252 million years ago

666
00:30:47,246 --> 00:30:49,815
were indeed part
of a global crisis.

667
00:30:51,450 --> 00:30:53,818
In the northeastern corner
of Pangaea,

668
00:30:53,819 --> 00:30:55,687
in what is now Siberia,

669
00:30:55,688 --> 00:30:57,922
one of the biggest volcanic
eruptions

670
00:30:57,923 --> 00:30:59,757
life on Earth has ever seen

671
00:30:59,758 --> 00:31:00,959
began.

672
00:31:00,960 --> 00:31:04,662
(eruption echoing)

673
00:31:04,663 --> 00:31:08,433
The scale of this event would
dwarf the Capitanian crisis.

674
00:31:08,434 --> 00:31:12,670
The lava spread across nearly
three million square miles,

675
00:31:12,671 --> 00:31:15,908
an area almost as large
as the U.S. Lower 48.

676
00:31:17,977 --> 00:31:22,047
The eruptions lasted
for at least 200,000 years.

677
00:31:23,682 --> 00:31:26,251
Consequences for life
were terrible.

678
00:31:26,252 --> 00:31:30,555
On land, around 70% of species
disappeared.

679
00:31:30,556 --> 00:31:33,258
In the seas,
the toll was even heavier.

680
00:31:33,259 --> 00:31:36,127
Changes in acidity
and oxygen levels

681
00:31:36,128 --> 00:31:39,998
wiped out
as many as 95% of species.

682
00:31:39,999 --> 00:31:42,367
(wind whipping)

683
00:31:42,368 --> 00:31:45,203
The greenhouse effect
also went into overdrive,

684
00:31:45,204 --> 00:31:48,340
causing temperatures
to rise dramatically.

685
00:31:49,441 --> 00:31:53,244
Paleontologists have dubbed
this event "the Great Dying,"

686
00:31:53,245 --> 00:31:55,848
and it marked the end
of the Permian period.

687
00:31:57,583 --> 00:31:59,951
BRUSATTE:
This was the closest
life has ever come

688
00:31:59,952 --> 00:32:01,519
to completely dying out.

689
00:32:01,520 --> 00:32:03,421
Our ancestors,

690
00:32:03,422 --> 00:32:07,492
they were there when it happened
and they made it through.

691
00:32:07,493 --> 00:32:11,663
And if they didn't,
then we wouldn't be here today.

692
00:32:11,664 --> 00:32:16,768
{\an8}NARRATOR:
This crisis heralded the start
of a new geological era.

693
00:32:16,769 --> 00:32:19,637
{\an8}It transformed the planet's
climate and landscape,

694
00:32:19,638 --> 00:32:22,073
{\an8}including in the Karoo.

695
00:32:22,074 --> 00:32:24,242
{\an8}But what was it like
to be there?

696
00:32:24,243 --> 00:32:26,144
{\an8}And what did this mean
for the many therapsids

697
00:32:26,145 --> 00:32:29,081
{\an8}that called this part
of the world home?

698
00:32:30,449 --> 00:32:33,184
♪ ♪

699
00:32:33,185 --> 00:32:35,253
At the Iziko South African
Museum,

700
00:32:35,254 --> 00:32:39,824
a dicynodont fossil sheds light
on the Karoo's climate.

701
00:32:39,825 --> 00:32:41,726
BROWNING:
So here we have the skull
of the animal.

702
00:32:41,727 --> 00:32:43,194
The head.

703
00:32:43,195 --> 00:32:46,197
There's the outline of one
of its eyes, front of its nose.

704
00:32:46,198 --> 00:32:48,833
And then coming around,
we have the front foot.

705
00:32:48,834 --> 00:32:51,302
The fingers are missing.

706
00:32:51,303 --> 00:32:52,670
Then, if you follow it along,

707
00:32:52,671 --> 00:32:53,738
here's the beautifully
articulated

708
00:32:53,739 --> 00:32:56,174
complete spine of the animal.

709
00:32:56,175 --> 00:32:58,309
And the animal's
kind of spread-eagle.

710
00:32:58,310 --> 00:33:01,346
NARRATOR:
This unusual position
can tell us

711
00:33:01,347 --> 00:33:03,081
how this dicynodont died.

712
00:33:03,082 --> 00:33:04,615
ROGER SMITH:
One of the ways in which

713
00:33:04,616 --> 00:33:06,517
an animal dies of exhaustion

714
00:33:06,518 --> 00:33:09,287
is actually by collapsing,

715
00:33:09,288 --> 00:33:10,988
and collapsing with its feet
spread out

716
00:33:10,989 --> 00:33:14,125
in this very distinctive
spread-eagle pose.

717
00:33:14,126 --> 00:33:17,929
NARRATOR:
In the Triassic Karoo,
therapsids struggled.

718
00:33:17,930 --> 00:33:21,999
Hunger, thirst, and exhaustion
were all common threats.

719
00:33:22,000 --> 00:33:23,801
What adaptations
made it possible

720
00:33:23,802 --> 00:33:25,137
for any of them to survive?

721
00:33:27,373 --> 00:33:31,242
♪ ♪

722
00:33:31,243 --> 00:33:33,478
In Bethulie, east of the Karoo,

723
00:33:33,479 --> 00:33:37,648
the remains of a species of
dicynodont known as Lystrosaurus

724
00:33:37,649 --> 00:33:39,618
have given us clues.

725
00:33:40,819 --> 00:33:42,620
SMITH:
This is an area
that I like to call

726
00:33:42,621 --> 00:33:44,489
the Lystrosaurus killing fields.

727
00:33:44,490 --> 00:33:47,892
I've been able to map
the actual embedded skeletons

728
00:33:47,893 --> 00:33:50,395
throughout this entire area.

729
00:33:50,396 --> 00:33:52,630
And I have 600
in situ skeletons already.

730
00:33:52,631 --> 00:33:54,699
So originally,
there must have been

731
00:33:54,700 --> 00:33:56,135
literally many thousands.

732
00:33:58,404 --> 00:34:01,939
{\an8}NARRATOR:
These dicynodonts represent
95% of the therapsid fossils

733
00:34:01,940 --> 00:34:05,777
{\an8}discovered in this area
from this time period.

734
00:34:05,778 --> 00:34:07,413
{\an8}But why were there so many here?

735
00:34:10,749 --> 00:34:14,085
Paleontologist Jennifer Botha
has discovered a clue hidden

736
00:34:14,086 --> 00:34:16,422
in the microstructure
of their bones.

737
00:34:18,891 --> 00:34:20,291
BOTHA:
What you are looking at here

738
00:34:20,292 --> 00:34:22,894
is a cross-section
through the bone.

739
00:34:22,895 --> 00:34:26,097
The organic components
of the bone have disappeared,

740
00:34:26,098 --> 00:34:28,299
but the position
of all the bone fibers

741
00:34:28,300 --> 00:34:30,201
have remained in place.

742
00:34:30,202 --> 00:34:33,304
So we can tell certain things
about how the animal grew.

743
00:34:33,305 --> 00:34:35,373
I can see these lines

744
00:34:35,374 --> 00:34:38,142
running down through here
through the bone.

745
00:34:38,143 --> 00:34:41,345
And they represent
yearly growth marks.

746
00:34:41,346 --> 00:34:43,781
So if I count
the number of growth marks,

747
00:34:43,782 --> 00:34:46,651
I can tell how old
the animal was when it died.

748
00:34:46,652 --> 00:34:50,455
NARRATOR:
But how can the age at death
shed light

749
00:34:50,456 --> 00:34:52,423
on why Lystrosaurus
was so prolific in the Karoo

750
00:34:52,424 --> 00:34:55,693
during the Triassic
after the Permian crisis?

751
00:34:55,694 --> 00:34:59,297
♪ ♪

752
00:34:59,298 --> 00:35:02,066
Here I have a Lystrosaurus
species from the Permian

753
00:35:02,067 --> 00:35:03,234
on the left

754
00:35:03,235 --> 00:35:05,903
and a Lystrosaurus species
from the Triassic

755
00:35:05,904 --> 00:35:07,972
on the right.

756
00:35:07,973 --> 00:35:10,541
And highlighted in green
are the number of growth marks

757
00:35:10,542 --> 00:35:12,343
I have been able to count.

758
00:35:12,344 --> 00:35:14,245
So I can tell that this animal

759
00:35:14,246 --> 00:35:16,914
was at least eight years old
when it died.

760
00:35:16,915 --> 00:35:20,718
In comparison,
this Triassic specimen

761
00:35:20,719 --> 00:35:24,355
was only at least two years old
when it died.

762
00:35:24,356 --> 00:35:26,457
And very importantly,

763
00:35:26,458 --> 00:35:30,461
this is a large
Lystrosaurus Permian species,

764
00:35:30,462 --> 00:35:33,297
and this is the largest known
Triassic specimen.

765
00:35:33,298 --> 00:35:35,800
So even the largest
Triassic specimens

766
00:35:35,801 --> 00:35:37,502
that we have ever discovered

767
00:35:37,503 --> 00:35:38,936
are not fully grown.

768
00:35:38,937 --> 00:35:41,772
They are at most
two or three years old.

769
00:35:41,773 --> 00:35:43,608
♪ ♪

770
00:35:43,609 --> 00:35:47,011
NARRATOR:
After the crisis,
Lystrosauruses were dying young.

771
00:35:47,012 --> 00:35:49,981
So what explains
their large population?

772
00:35:49,982 --> 00:35:51,449
In order to be so abundant,

773
00:35:51,450 --> 00:35:54,252
they had to be breeding
quite abundantly.

774
00:35:54,253 --> 00:35:58,523
NARRATOR:
This suggests that the
birth rate increased rapidly.

775
00:35:58,524 --> 00:36:02,661
♪ ♪

776
00:36:04,563 --> 00:36:05,630
During periods of drought,

777
00:36:05,631 --> 00:36:08,267
times were tough
for all the animals here.

778
00:36:10,569 --> 00:36:13,371
{\an8}Predators, who depended
on the herbivores for food,

779
00:36:13,372 --> 00:36:14,840
{\an8}went hungry.

780
00:36:17,042 --> 00:36:18,609
{\an8}The carnivorous gorgonopsians

781
00:36:18,610 --> 00:36:21,647
{\an8}succumbed to the hostile
conditions and vanished.

782
00:36:23,749 --> 00:36:25,884
{\an8}And so did the biarmosuchians.

783
00:36:30,856 --> 00:36:33,491
{\an8}The dicynodonts
were dying young,

784
00:36:33,492 --> 00:36:37,295
{\an8}but their rapid reproduction
rates and their burrowing habits

785
00:36:37,296 --> 00:36:39,631
{\an8}helped them survive
this period's climate chaos.

786
00:36:43,201 --> 00:36:44,869
{\an8}The therocephalians
initially made it,

787
00:36:44,870 --> 00:36:48,941
{\an8}but as time went on,
they, too, eventually died out.

788
00:36:50,142 --> 00:36:53,712
{\an8}The cynodonts survived
this tumultuous period, barely.

789
00:36:54,713 --> 00:36:58,015
Only two groups remained:

790
00:36:58,016 --> 00:37:00,084
the dicynodonts

791
00:37:00,085 --> 00:37:01,653
and the cynodonts.

792
00:37:04,890 --> 00:37:07,058
♪ ♪

793
00:37:07,059 --> 00:37:10,629
The fossil record shows just how
successful the dicynodonts were.

794
00:37:12,164 --> 00:37:14,932
{\an8}(translated):
This is what this
animal looked like.

795
00:37:14,933 --> 00:37:17,301
{\an8}It was about 50 to 70
centimeters long,

796
00:37:17,302 --> 00:37:18,937
{\an8}so about the size
of a small pig.

797
00:37:21,340 --> 00:37:23,774
{\an8}Dicynodonts literally swarmed

798
00:37:23,775 --> 00:37:26,711
{\an8}during the first five million
years of the Triassic period.

799
00:37:26,712 --> 00:37:28,846
{\an8}So much so that they
rediversified

800
00:37:28,847 --> 00:37:31,415
{\an8}and gave rise
to large herbivores,

801
00:37:31,416 --> 00:37:34,452
as illustrated here
by this skull,

802
00:37:34,453 --> 00:37:36,520
which belonged to an animal
that must have been roughly

803
00:37:36,521 --> 00:37:40,491
the size of a modern wildebeest,
weighing several hundred kilos.

804
00:37:40,492 --> 00:37:42,493
(speaking French)

805
00:37:42,494 --> 00:37:45,997
(translated):
And these giant dicynodonts
repopulated the world.

806
00:37:45,998 --> 00:37:47,732
They spread
across the whole of Pangaea.

807
00:37:47,733 --> 00:37:49,967
(bellows)

808
00:37:49,968 --> 00:37:52,169
NARRATOR:
Fossil remains of dicynodonts
have been found

809
00:37:52,170 --> 00:37:53,371
on every continent.

810
00:37:53,372 --> 00:37:57,141
But the dicynodonts
weren't the only group

811
00:37:57,142 --> 00:37:59,176
that found a way to adapt
to their new environment.

812
00:37:59,177 --> 00:38:01,946
Paleontologist Roger Smith
has found a fossil

813
00:38:01,947 --> 00:38:05,282
that reveals
that some of the cynodonts

814
00:38:05,283 --> 00:38:07,251
had discovered
some of the same tricks.

815
00:38:07,252 --> 00:38:10,621
♪ ♪

816
00:38:10,622 --> 00:38:13,891
SMITH:
Here we have
an underground burrow cast

817
00:38:13,892 --> 00:38:16,861
made into the ancient floodplain
by a cynodont.

818
00:38:16,862 --> 00:38:20,765
The architecture
of the cynodont burrow

819
00:38:20,766 --> 00:38:23,534
is a tube going into the ground,
and when it gets to the end,

820
00:38:23,535 --> 00:38:26,270
it forms this round
terminal chamber.

821
00:38:26,271 --> 00:38:28,305
This doesn't have a skeleton
in it.

822
00:38:28,306 --> 00:38:29,640
If it did have a skeleton--

823
00:38:29,641 --> 00:38:31,409
and we do have skeletons
in these--

824
00:38:31,410 --> 00:38:33,044
they're curled up generally

825
00:38:33,045 --> 00:38:34,845
with their back to the outside,

826
00:38:34,846 --> 00:38:39,150
with the tail curled around
against the wall.

827
00:38:39,151 --> 00:38:42,153
This burrow cast could well be

828
00:38:42,154 --> 00:38:46,524
a behavioral adaptation of
the cynodonts to go underground

829
00:38:46,525 --> 00:38:48,826
to escape the extremes of heat
during the day and night,

830
00:38:48,827 --> 00:38:51,696
and perhaps to even breed.

831
00:38:51,697 --> 00:38:53,898
{\an8}Being able to burrow,

832
00:38:53,899 --> 00:38:56,233
{\an8}that was a major
survival strategy.

833
00:38:56,234 --> 00:38:57,635
Being able to hide away.

834
00:38:57,636 --> 00:38:59,170
And that is probably one
of the things

835
00:38:59,171 --> 00:39:02,907
that enabled our ancestors
to endure.

836
00:39:02,908 --> 00:39:06,410
NARRATOR:
The same adaptations
that helped the dicynodonts

837
00:39:06,411 --> 00:39:09,914
emerge from the first crisis
eight million years before

838
00:39:09,915 --> 00:39:13,017
also helped
the cynodonts survive.

839
00:39:13,018 --> 00:39:16,153
♪ ♪

840
00:39:16,154 --> 00:39:19,590
As the ecosystem
recovered from the crisis,

841
00:39:19,591 --> 00:39:22,326
the cynodonts led
a relatively stable existence.

842
00:39:22,327 --> 00:39:25,062
(growls, jaws clamp)

843
00:39:25,063 --> 00:39:28,065
But according
to the fossil record,

844
00:39:28,066 --> 00:39:30,367
the dicynodonts really thrived.

845
00:39:30,368 --> 00:39:33,037
♪ ♪

846
00:39:33,038 --> 00:39:35,539
Freed from the
gorgonopsian threat,

847
00:39:35,540 --> 00:39:38,909
they took full advantage
of available ecological niches

848
00:39:38,910 --> 00:39:40,879
and grew many times larger.

849
00:39:44,082 --> 00:39:45,449
Meanwhile, the therapsids

850
00:39:45,450 --> 00:39:46,951
weren't the only creatures
doing well.

851
00:39:46,952 --> 00:39:50,021
{\an8}Others were starting to appear.

852
00:39:53,225 --> 00:39:55,259
{\an8}JONAH CHOINIERE:
The top predators
of the late Triassic

853
00:39:55,260 --> 00:39:57,027
are things called
pseudosuchians.

854
00:39:57,028 --> 00:39:59,196
They're sort of the cousins
of dinosaurs.

855
00:39:59,197 --> 00:40:01,532
They look a bit
like modern crocs.

856
00:40:01,533 --> 00:40:03,368
They're covered in body armor
along their back.

857
00:40:05,070 --> 00:40:07,872
{\an8}NARRATOR:
Soon to be found in almost
every corner of the globe,

858
00:40:07,873 --> 00:40:09,173
{\an8}they are evidence

859
00:40:09,174 --> 00:40:12,143
{\an8}of yet another planet-wide
environmental change:

860
00:40:12,144 --> 00:40:13,978
{\an8}one that would greatly impact

861
00:40:13,979 --> 00:40:16,615
{\an8}the therapsids
and their mammal descendants.

862
00:40:19,918 --> 00:40:22,553
232 million-year-old
plant fossils

863
00:40:22,554 --> 00:40:25,089
show new flora was developing:

864
00:40:25,090 --> 00:40:26,724
the type of plants
that only exist

865
00:40:26,725 --> 00:40:28,426
in extremely rainy climates.

866
00:40:30,662 --> 00:40:33,397
Heavy rainfall
was a planet-wide phenomenon,

867
00:40:33,398 --> 00:40:35,966
and paleontologists have
dubbed this period

868
00:40:35,967 --> 00:40:38,536
"the Carnian pluvial episode."

869
00:40:38,537 --> 00:40:40,137
Over about two million years,

870
00:40:40,138 --> 00:40:43,007
the climate changed
from extreme to extreme:

871
00:40:43,008 --> 00:40:44,642
cold to hot,

872
00:40:44,643 --> 00:40:48,112
dry to wet.

873
00:40:48,113 --> 00:40:51,682
In the Karoo,
the desert turned green.

874
00:40:51,683 --> 00:40:56,487
But only one therapsid lineage
would survive this time.

875
00:40:56,488 --> 00:40:59,690
Would it be the thriving
and vastly varied dicynodonts

876
00:40:59,691 --> 00:41:03,527
or the newly emerged cynodonts?

877
00:41:03,528 --> 00:41:07,031
Which would give rise
to all of mammal-kind?

878
00:41:07,032 --> 00:41:09,333
To us?
(animal growls, jaws clamp)

879
00:41:09,334 --> 00:41:12,570
The remaining therapsids
had to contend

880
00:41:12,571 --> 00:41:14,873
with new creatures dominating
the Karoo.

881
00:41:15,974 --> 00:41:18,008
{\an8}Dinosaurs, like the ones
in front of me,

882
00:41:18,009 --> 00:41:20,010
soon become the most dominant
large-bodied animals

883
00:41:20,011 --> 00:41:21,312
on the landscape.

884
00:41:21,313 --> 00:41:23,080
The therapsids
and the other animals

885
00:41:23,081 --> 00:41:24,615
that were once so common
on landscapes

886
00:41:24,616 --> 00:41:26,617
become much more rare.

887
00:41:26,618 --> 00:41:28,986
And instead of seeing therapsids
eating plants,

888
00:41:28,987 --> 00:41:31,255
we'd be seeing dinosaurs
like this one

889
00:41:31,256 --> 00:41:34,158
browsing on the vegetation.

890
00:41:34,159 --> 00:41:36,060
NARRATOR:
It was also a time
when new characteristics

891
00:41:36,061 --> 00:41:37,795
that would prove helpful
for survival

892
00:41:37,796 --> 00:41:39,964
were appearing.

893
00:41:39,965 --> 00:41:43,133
And one in particular,
a very mammal-like quality,

894
00:41:43,134 --> 00:41:47,037
may have been
the biggest advantage of all:

895
00:41:47,038 --> 00:41:50,040
a metabolism
that kept the body warm.

896
00:41:50,041 --> 00:41:53,644
Being warm-blooded
is really important.

897
00:41:53,645 --> 00:41:57,281
It means that we can go outside
when it's wintertime.

898
00:41:57,282 --> 00:42:00,084
It means that we can be active
in the morning

899
00:42:00,085 --> 00:42:01,852
or when the sun's not out.

900
00:42:01,853 --> 00:42:03,587
You're not
like a cold-blooded animal

901
00:42:03,588 --> 00:42:05,522
that's at the mercy of the sun.

902
00:42:05,523 --> 00:42:07,391
And that's really unusual.

903
00:42:07,392 --> 00:42:08,759
It's a superpower.

904
00:42:08,760 --> 00:42:12,763
NARRATOR:
Modern-day mammals
are warm-blooded.

905
00:42:12,764 --> 00:42:14,298
When did this trait emerge?

906
00:42:14,299 --> 00:42:16,667
And how?

907
00:42:16,668 --> 00:42:18,302
It is really challenging

908
00:42:18,303 --> 00:42:20,771
to figure out
if a fossil species

909
00:42:20,772 --> 00:42:22,139
was warm-blooded
or cold-blooded.

910
00:42:22,140 --> 00:42:25,009
You can't just stick
a thermometer into them

911
00:42:25,010 --> 00:42:26,477
and see how their body
temperature changes

912
00:42:26,478 --> 00:42:27,745
over the day.

913
00:42:27,746 --> 00:42:29,480
So you have to look for clues
in the fossils.

914
00:42:29,481 --> 00:42:32,149
There's one
very interesting clue,

915
00:42:32,150 --> 00:42:34,752
this opening
in the top of the head

916
00:42:34,753 --> 00:42:36,787
for what's called a third eye.

917
00:42:36,788 --> 00:42:38,989
It's, it's a bunch of cells
that sense light.

918
00:42:38,990 --> 00:42:41,358
NARRATOR:
It's thought
that the third eye

919
00:42:41,359 --> 00:42:43,360
helped
ancient cold-blooded therapsids

920
00:42:43,361 --> 00:42:46,830
regulate their daily activities.

921
00:42:46,831 --> 00:42:49,533
(translated):
In modern species,
the third eye only exists

922
00:42:49,534 --> 00:42:52,369
among cold-blooded animals.

923
00:42:52,370 --> 00:42:54,705
Therefore, the disappearance
of the third eye may be linked

924
00:42:54,706 --> 00:42:57,875
to the appearance
of warm-blooded metabolism.

925
00:42:57,876 --> 00:42:59,910
My colleagues and I decided
to look

926
00:42:59,911 --> 00:43:03,747
for when the therapsids lost
this third eye.

927
00:43:03,748 --> 00:43:06,150
(speaking French)

928
00:43:06,151 --> 00:43:08,585
NARRATOR:
Julien and his team have
studied fossils

929
00:43:08,586 --> 00:43:10,955
from across the reign
of the therapsids,

930
00:43:10,956 --> 00:43:14,892
all the way back
to almost 270 million years ago,

931
00:43:14,893 --> 00:43:18,862
in the Permian period,
before the Great Dying.

932
00:43:18,863 --> 00:43:22,367
In the Permian, almost all
therapsids had a third eye.

933
00:43:24,202 --> 00:43:26,971
(translated):
Then, when we enter
the Triassic,

934
00:43:26,972 --> 00:43:31,075
the first Triassic species
still had a third eye.

935
00:43:31,076 --> 00:43:32,409
But a little later,

936
00:43:32,410 --> 00:43:34,745
we begin to encounter species
that no longer have

937
00:43:34,746 --> 00:43:36,780
a hole at the top
of their skull.

938
00:43:36,781 --> 00:43:40,184
They no longer had a third eye.

939
00:43:40,185 --> 00:43:43,253
NARRATOR:
By 240 million years ago,
the third eye

940
00:43:43,254 --> 00:43:45,589
had all but vanished
from the fossil record

941
00:43:45,590 --> 00:43:49,593
of one therapsid group,
the cynodonts.

942
00:43:49,594 --> 00:43:52,463
This isn't definitive proof
of warm blood,

943
00:43:52,464 --> 00:43:56,367
but scientists
have found another clue.

944
00:43:56,368 --> 00:43:59,804
BENOÎT (translated):
The most decisive argument
was the study of the inner ear.

945
00:44:01,106 --> 00:44:04,508
NARRATOR:
The warmer the internal
body temperature of an animal,

946
00:44:04,509 --> 00:44:06,877
{\an8}the runnier
their ear canal fluid becomes

947
00:44:06,878 --> 00:44:09,980
{\an8}and the thinner
the tubes can be.

948
00:44:09,981 --> 00:44:12,016
(translated):
We were able to measure changes

949
00:44:12,017 --> 00:44:13,951
in the size of the canals
in cynodonts

950
00:44:13,952 --> 00:44:16,487
and determine precisely
that the body temperature

951
00:44:16,488 --> 00:44:18,322
{\an8}had increased
by ten degrees

952
00:44:18,323 --> 00:44:19,323
{\an8}exactly here,

953
00:44:19,324 --> 00:44:21,025
{\an8}between this
Triassic animal

954
00:44:21,026 --> 00:44:22,026
{\an8}and this animal

955
00:44:22,027 --> 00:44:25,430
{\an8}233 million
years ago.

956
00:44:27,665 --> 00:44:29,800
NARRATOR:
Evidence suggests
that the cynodonts

957
00:44:29,801 --> 00:44:33,670
were warm-blooded during
the Carnian pluvial episode.

958
00:44:33,671 --> 00:44:36,040
BRUSATTE:
There was a time
of, of fairly rapid change

959
00:44:36,041 --> 00:44:38,342
in climate and in precipitation,

960
00:44:38,343 --> 00:44:39,543
and being warm-blooded

961
00:44:39,544 --> 00:44:41,712
would have been beneficial
at that time,

962
00:44:41,713 --> 00:44:44,982
because if you can control
your own body temperature,

963
00:44:44,983 --> 00:44:47,918
that can protect you
from the whims of the weather.

964
00:44:47,919 --> 00:44:50,888
NARRATOR:
What did this mean
for therapsids

965
00:44:50,889 --> 00:44:52,890
that were not warm-blooded?

966
00:44:52,891 --> 00:44:55,392
(translated):
This Carnian rainfall event had

967
00:44:55,393 --> 00:44:56,828
a huge impact on the therapsids.

968
00:44:59,030 --> 00:45:01,198
{\an8}NARRATOR:
By about 200 million years ago,

969
00:45:01,199 --> 00:45:04,201
{\an8}the dicynodonts disappear
from the fossil record.

970
00:45:04,202 --> 00:45:06,970
{\an8}(bellows)

971
00:45:06,971 --> 00:45:09,006
(translated):
There was one small group
that came out on top,

972
00:45:09,007 --> 00:45:10,374
the cynodonts.

973
00:45:10,375 --> 00:45:13,444
And this group is the one
that gave rise to mammals.

974
00:45:13,445 --> 00:45:15,913
(speaking French)

975
00:45:15,914 --> 00:45:18,582
BRUSATTE:
It was the small size
of these cynodonts,

976
00:45:18,583 --> 00:45:22,086
their ability to dig burrows,
being able to grow fast,

977
00:45:22,087 --> 00:45:23,854
being able to eat
lots of different foods.

978
00:45:23,855 --> 00:45:25,355
That's what helped
make them through.

979
00:45:25,356 --> 00:45:27,558
And then on the other side,
they would have found

980
00:45:27,559 --> 00:45:29,426
this wide-open world,

981
00:45:29,427 --> 00:45:31,929
a land of new frontiers
and opportunities.

982
00:45:31,930 --> 00:45:33,630
(thunder claps)

983
00:45:33,631 --> 00:45:36,366
NARRATOR:
230 million years ago,
the cynodonts were just starting

984
00:45:36,367 --> 00:45:39,336
to adapt to this new world.

985
00:45:39,337 --> 00:45:42,206
How did they give rise
to mammals

986
00:45:42,207 --> 00:45:43,740
just five million years later?

987
00:45:43,741 --> 00:45:46,176
{\an8}When did
the other key mammal traits,

988
00:45:46,177 --> 00:45:48,345
{\an8}lactation and hair,

989
00:45:48,346 --> 00:45:50,348
{\an8}appear in their evolution?

990
00:45:52,617 --> 00:45:54,384
(translated): Hair is the
insulating layer

991
00:45:54,385 --> 00:45:56,887
that allows mammals
to retain heat.

992
00:45:56,888 --> 00:45:58,388
(growling softly)

993
00:45:58,389 --> 00:46:01,391
NARRATOR:
The rarity of hair or fur
in the fossil record

994
00:46:01,392 --> 00:46:03,093
has made it difficult
for scientists to find exactly

995
00:46:03,094 --> 00:46:07,064
when this mammal trait evolved.

996
00:46:07,065 --> 00:46:09,900
But there is one type of hair
that leaves a mark:

997
00:46:09,901 --> 00:46:12,136
whiskers.

998
00:46:12,137 --> 00:46:14,404
And although mammals
are not the only animals

999
00:46:14,405 --> 00:46:15,606
with whisker-like features
today,

1000
00:46:15,607 --> 00:46:20,377
they're a sure sign
that hair has evolved.

1001
00:46:20,378 --> 00:46:21,545
(translated):
We can track the evolution
of whiskers

1002
00:46:21,546 --> 00:46:24,181
thanks to traces left behind

1003
00:46:24,182 --> 00:46:25,582
by the nerve
which makes them sensitive.

1004
00:46:25,583 --> 00:46:27,986
(speaking French)

1005
00:46:29,053 --> 00:46:30,954
NARRATOR:
Whiskers help mammals
detect small changes

1006
00:46:30,955 --> 00:46:32,856
in the world around them,

1007
00:46:32,857 --> 00:46:37,094
find prey,
and even communicate.

1008
00:46:37,095 --> 00:46:39,196
{\an8}They're incredibly sensitive
to external surroundings.

1009
00:46:39,197 --> 00:46:41,131
{\an8}This is because

1010
00:46:41,132 --> 00:46:43,233
{\an8}they are connected directly
to the brain

1011
00:46:43,234 --> 00:46:44,369
{\an8}by the trigeminal nerve.

1012
00:46:46,137 --> 00:46:48,939
{\an8}It's evidence of how this nerve
emerged from cynodont skulls

1013
00:46:48,940 --> 00:46:52,309
{\an8}that has revealed when whiskers
first appeared in this line.

1014
00:46:52,310 --> 00:46:55,179
{\an8}♪ ♪

1015
00:46:55,180 --> 00:46:57,080
(Benoît speaking French)

1016
00:46:57,081 --> 00:47:00,284
(translated):
In animals that lived
around 230 million years ago,

1017
00:47:00,285 --> 00:47:01,585
a single hole appears,

1018
00:47:01,586 --> 00:47:05,789
which is exactly what we find
in modern mammals.

1019
00:47:05,790 --> 00:47:07,658
This single hole
is the passageway

1020
00:47:07,659 --> 00:47:08,892
for the trigeminal nerve,

1021
00:47:08,893 --> 00:47:11,428
which innervates the whiskers,
located here,

1022
00:47:11,429 --> 00:47:13,565
in this cavity.

1023
00:47:15,200 --> 00:47:17,034
NARRATOR:
This creature had whiskers

1024
00:47:17,035 --> 00:47:19,203
just after the Carnian pluvial
episode,

1025
00:47:19,204 --> 00:47:22,039
around the same time
warm-bloodedness appeared.

1026
00:47:22,040 --> 00:47:23,707
Coincidence?

1027
00:47:23,708 --> 00:47:25,509
Or could they be linked?

1028
00:47:25,510 --> 00:47:28,212
{\an8}Typically, traits evolve
at different rates

1029
00:47:28,213 --> 00:47:30,113
over millions of years

1030
00:47:30,114 --> 00:47:33,217
unless they are somehow
connected.

1031
00:47:33,218 --> 00:47:35,986
The final missing piece
in the puzzle

1032
00:47:35,987 --> 00:47:38,322
is the appearance of lactation,

1033
00:47:38,323 --> 00:47:41,058
mothers producing milk
to feed their young.

1034
00:47:41,059 --> 00:47:42,093
When did that appear?

1035
00:47:45,196 --> 00:47:48,665
Lactation is tough to spot
in the fossil record,

1036
00:47:48,666 --> 00:47:52,469
so scientists have instead
turned to DNA for answers,

1037
00:47:52,470 --> 00:47:54,605
with tantalizing results.

1038
00:47:54,606 --> 00:47:57,574
The evolution of a single gene
seems to be related

1039
00:47:57,575 --> 00:48:01,111
to all three mammalian traits.

1040
00:48:01,112 --> 00:48:03,347
(translated):
The MSX2 gene controlled

1041
00:48:03,348 --> 00:48:04,881
{\an8}not only the disappearance
of the third eye

1042
00:48:04,882 --> 00:48:06,483
{\an8}and the appearance of hair,

1043
00:48:06,484 --> 00:48:08,752
{\an8}but also the appearance
of mammary glands,

1044
00:48:08,753 --> 00:48:10,787
{\an8}and, with that, lactation.

1045
00:48:10,788 --> 00:48:13,790
{\an8}This is the most
characteristic trait of mammals.

1046
00:48:13,791 --> 00:48:16,326
{\an8}(speaking French)

1047
00:48:16,327 --> 00:48:21,365
{\an8}NARRATOR:
The evolution of MSX2
contributed to the emergence

1048
00:48:21,366 --> 00:48:23,800
{\an8}of these mammalian features
in cynodonts,

1049
00:48:23,801 --> 00:48:27,971
{\an8}which they then passed on
to their mammal descendants,

1050
00:48:27,972 --> 00:48:29,606
giving them
the defining characteristics

1051
00:48:29,607 --> 00:48:31,575
of all mammal-kind.

1052
00:48:31,576 --> 00:48:32,976
But it's not the only gene
responsible

1053
00:48:32,977 --> 00:48:34,611
for big evolutionary changes.

1054
00:48:34,612 --> 00:48:38,382
Whether it's turning
fish fins into limbs

1055
00:48:38,383 --> 00:48:40,817
or developing a spoken language,

1056
00:48:40,818 --> 00:48:42,519
there is a set
of key regulator genes

1057
00:48:42,520 --> 00:48:43,920
that have a profound impact

1058
00:48:43,921 --> 00:48:46,758
on development
and evolutionary change.

1059
00:48:48,459 --> 00:48:52,095
{\an8}At the boundary between the
Triassic and Jurassic periods,

1060
00:48:52,096 --> 00:48:55,132
{\an8}the dicynodont group
had gone extinct

1061
00:48:55,133 --> 00:48:57,902
{\an8}and the cynodonts were the
last surviving therapsids.

1062
00:48:59,871 --> 00:49:02,439
{\an8}So at last,
we have an answer.

1063
00:49:02,440 --> 00:49:05,309
{\an8}This is the group that
gave rise to the mammal line

1064
00:49:05,310 --> 00:49:09,913
{\an8}around 225 million years ago,

1065
00:49:09,914 --> 00:49:11,815
{\an8}not long before the other
therapsid lineages ended.

1066
00:49:11,816 --> 00:49:14,618
{\an8}(thunder claps, animal chitters)

1067
00:49:14,619 --> 00:49:17,354
{\an8}The very first true mammals

1068
00:49:17,355 --> 00:49:18,855
{\an8}were tiny.

1069
00:49:18,856 --> 00:49:20,691
{\an8}And if you saw one,
it would have looked

1070
00:49:20,692 --> 00:49:22,326
{\an8}like a little mouse
or a little shrew.

1071
00:49:22,327 --> 00:49:23,927
{\an8}They would have been covered
in hair.

1072
00:49:23,928 --> 00:49:25,228
{\an8}They would have had molar teeth.

1073
00:49:25,229 --> 00:49:26,997
{\an8}They would have fed their babies
milk.

1074
00:49:26,998 --> 00:49:29,299
{\an8}You would recognize them
as mammals,

1075
00:49:29,300 --> 00:49:31,134
but you would probably
just think they were

1076
00:49:31,135 --> 00:49:33,271
some kind of little rodent
scurrying around.

1077
00:49:35,039 --> 00:49:37,808
{\an8}NARRATOR:
It wasn't easy
for the newly evolved mammals,

1078
00:49:37,809 --> 00:49:39,576
{\an8}as the dinosaurs reigned

1079
00:49:39,577 --> 00:49:43,547
{\an8}for roughly
the next 160 million years.

1080
00:49:43,548 --> 00:49:44,948
{\an8}The fates of dinosaurs
and mammals

1081
00:49:44,949 --> 00:49:46,249
{\an8}have always been intertwined.

1082
00:49:46,250 --> 00:49:48,452
{\an8}And while dinosaurs took over
the world,

1083
00:49:48,453 --> 00:49:49,920
mammals went the other way.

1084
00:49:49,921 --> 00:49:51,655
They went small.

1085
00:49:51,656 --> 00:49:53,523
They evolved
stronger jaw muscles

1086
00:49:53,524 --> 00:49:55,325
so they could bite harder.

1087
00:49:55,326 --> 00:49:57,494
They evolved a keener sense
of hearing.

1088
00:49:57,495 --> 00:49:59,229
All these things
would have helped them

1089
00:49:59,230 --> 00:50:04,501
survive in a world controlled
by massive, enormous dinosaurs

1090
00:50:04,502 --> 00:50:07,104
that could have smashed
one of these little mammals

1091
00:50:07,105 --> 00:50:09,539
with a single footstep.

1092
00:50:09,540 --> 00:50:11,208
NARRATOR:
As had been the case
for the therapsids

1093
00:50:11,209 --> 00:50:13,710
in the extinction events
they faced,

1094
00:50:13,711 --> 00:50:16,480
it would be primarily
the smallest of the mammals

1095
00:50:16,481 --> 00:50:19,816
that would survive
the next major crisis:

1096
00:50:19,817 --> 00:50:22,686
the asteroid strike
that wiped out the dinosaurs

1097
00:50:22,687 --> 00:50:25,622
66 million years ago.

1098
00:50:25,623 --> 00:50:27,023
BROWNING:
Our ancestors made it
through that boundary

1099
00:50:27,024 --> 00:50:29,192
{\an8}for very specific reasons.

1100
00:50:29,193 --> 00:50:32,028
{\an8}We had very specific adaptations
as a group

1101
00:50:32,029 --> 00:50:34,632
{\an8}that allowed us to make it
past these extinction events.

1102
00:50:36,234 --> 00:50:38,368
NARRATOR:
Over millions of years
of evolution,

1103
00:50:38,369 --> 00:50:42,372
cynodonts,
these small burrowing animals,

1104
00:50:42,373 --> 00:50:44,374
survived multiple crises,

1105
00:50:44,375 --> 00:50:47,177
adapting and changing to fit
each new environment.

1106
00:50:47,178 --> 00:50:48,812
(thunder claps)

1107
00:50:48,813 --> 00:50:52,482
They gave rise to the mammals
some 200 million years ago,

1108
00:50:52,483 --> 00:50:53,884
at a time when the dinosaurs

1109
00:50:53,885 --> 00:50:56,186
were just beginning their reign
on Earth.

1110
00:50:56,187 --> 00:50:59,890
Mammals were not born

1111
00:50:59,891 --> 00:51:02,125
as a result of the extinction
of the dinosaurs,

1112
00:51:02,126 --> 00:51:05,395
but had appeared
millions of years before.

1113
00:51:05,396 --> 00:51:08,231
{\an8}For 160 million years,

1114
00:51:08,232 --> 00:51:12,135
{\an8}they lived
alongside these giants.

1115
00:51:12,136 --> 00:51:14,237
{\an8}And only once the dinosaurs
were extinct

1116
00:51:14,238 --> 00:51:16,940
{\an8}could the surviving mammals
rise,

1117
00:51:16,941 --> 00:51:20,143
{\an8}diversifying
into the spectacular variety

1118
00:51:20,144 --> 00:51:21,211
{\an8}we see today.

1119
00:51:21,212 --> 00:51:23,246
{\an8}♪ ♪

1120
00:51:23,247 --> 00:51:25,015
BRUSATTE:
We and all mammals alive today,

1121
00:51:25,016 --> 00:51:28,351
we are the descendants
of survivors.

1122
00:51:28,352 --> 00:51:29,553
So ultimately,

1123
00:51:29,554 --> 00:51:32,656
we come from this line

1124
00:51:32,657 --> 00:51:34,825
that's been small, adaptable,

1125
00:51:34,826 --> 00:51:38,128
a line that's been resilient,
that could handle everything

1126
00:51:38,129 --> 00:51:40,197
that nature's been able
to throw at us

1127
00:51:40,198 --> 00:51:42,299
over hundreds of millions
of years.

1128
00:51:42,300 --> 00:51:45,535
♪ ♪

1129
00:51:45,536 --> 00:51:47,971
NARRATOR:
With more than 270 million years

1130
00:51:47,972 --> 00:51:50,507
of shared evolution
running through our veins...

1131
00:51:50,508 --> 00:51:52,509
(roaring)

1132
00:51:52,510 --> 00:51:54,978
...we are therapsids...

1133
00:51:54,979 --> 00:51:58,181
(growling)

1134
00:51:58,182 --> 00:52:02,452
...just one of the thousands
of modern mammal species

1135
00:52:02,453 --> 00:52:05,522
that are their descendants.

1136
00:52:05,523 --> 00:52:08,225
Long live the therapsids.

1137
00:52:08,226 --> 00:52:10,527
(jaws clamp)

1138
00:52:10,528 --> 00:52:13,531
♪ ♪