1 00:00:02,288 --> 00:00:04,088 Meet the original Jaws, 2 00:00:05,130 --> 00:00:08,619 the 400 million year old nightmare, 3 00:00:08,620 --> 00:00:11,519 one of the first jawed fish. 4 00:00:11,520 --> 00:00:14,490 Basically, one of the first jawed anything. 5 00:00:14,491 --> 00:00:16,711 (dramatic music) 6 00:00:16,712 --> 00:00:21,419 Dunkleosteus, it's one of the greatest fishes of all time. 7 00:00:21,420 --> 00:00:25,209 It's about 40 feet long, it's head is bigger than I am 8 00:00:25,210 --> 00:00:27,459 {\an8}and it's jaws look like paper cutters, 9 00:00:27,460 --> 00:00:29,163 {\an8}just great big sharpened blades. 10 00:00:30,810 --> 00:00:33,047 Dunkleosteus was just one of dozens 11 00:00:33,048 --> 00:00:35,569 of doomed sea monsters that arose 12 00:00:35,570 --> 00:00:40,053 during the Devonian period also known as the fishes. 13 00:00:41,000 --> 00:00:43,250 And like all the rest of them from this time, 14 00:00:45,000 --> 00:00:46,300 it was slated for death 15 00:00:47,150 --> 00:00:50,626 by a barely believable series of disasters. 16 00:00:50,627 --> 00:00:53,377 (dramatic music) 17 00:01:04,180 --> 00:01:07,529 The Devonian spans about 50 million years, 18 00:01:07,530 --> 00:01:11,353 some 180 million years before the dinosaurs appeared. 19 00:01:13,560 --> 00:01:16,269 It's magnificent predators all descended 20 00:01:16,270 --> 00:01:18,399 from boneless fish that squeaked 21 00:01:18,400 --> 00:01:20,620 through the Earth's first mass extinction 22 00:01:21,543 --> 00:01:24,556 along with a handful of trilobites, 23 00:01:24,557 --> 00:01:28,083 conodonts, and other lifeforms. 24 00:01:29,967 --> 00:01:33,159 {\an8}There were crinoids, these stemmed sea lilies. 25 00:01:33,160 --> 00:01:34,713 {\an8}There were coral reefs. 26 00:01:35,700 --> 00:01:38,039 There were of course lots of fish. 27 00:01:38,040 --> 00:01:40,590 There were nautiloids that come back, some of them. 28 00:01:41,750 --> 00:01:44,529 In the sea we call it the age of fishes 29 00:01:44,530 --> 00:01:47,449 because now the fishes have evolved, 30 00:01:47,450 --> 00:01:49,853 they're diversifying and you get some whoppers. 31 00:01:52,570 --> 00:01:54,179 The massive supercontinent 32 00:01:54,180 --> 00:01:58,279 of Gondwana made up of South America, Africa, 33 00:01:58,280 --> 00:02:03,280 Antarctica, India, and Australia is drifting away 34 00:02:03,450 --> 00:02:06,273 from the South Pole toward warmer latitudes. 35 00:02:08,492 --> 00:02:10,549 What is now North America and what is now 36 00:02:10,550 --> 00:02:14,229 Europe had collided and raised up the land. 37 00:02:14,230 --> 00:02:17,928 So for the first time you had this big land area 38 00:02:17,929 --> 00:02:20,699 with mountains and rivers running off 39 00:02:20,700 --> 00:02:23,549 of the mountains into the sea. 40 00:02:23,550 --> 00:02:25,628 Today we know this mountain chain 41 00:02:25,629 --> 00:02:28,653 as the relatively diminutive Appalachians. 42 00:02:29,610 --> 00:02:33,093 Back then they'd have risen higher than the Himalayas. 43 00:02:34,000 --> 00:02:37,269 And when they came thrusting up out of the earth, 44 00:02:37,270 --> 00:02:40,313 life on the planet would never be the same. 45 00:02:41,780 --> 00:02:43,639 {\an8}The uplift of the Appalachians during this 46 00:02:43,640 --> 00:02:47,419 {\an8}time period is a very big deal geologically. 47 00:02:47,420 --> 00:02:51,559 You have a major mountain chain closing off a seaway, 48 00:02:51,560 --> 00:02:53,599 so they're changing your climate globally 49 00:02:53,600 --> 00:02:56,300 because you're cutting off ocean circulation pathways. 50 00:02:58,310 --> 00:03:01,129 But there's another factor and that is all during 51 00:03:01,130 --> 00:03:05,699 this period of early life algae were producing oxygen 52 00:03:05,700 --> 00:03:08,229 as a waste product of photosynthesis. 53 00:03:08,230 --> 00:03:11,469 If you make enough oxygen, it goes into the atmosphere, 54 00:03:11,470 --> 00:03:15,179 that oxygen is hit by ultraviolet radiation 55 00:03:15,180 --> 00:03:17,289 and it changes into ozone. 56 00:03:17,290 --> 00:03:21,999 So the planet really sort of makes itself habitable 57 00:03:22,000 --> 00:03:24,559 by first letting life produce oxygen 58 00:03:24,560 --> 00:03:27,339 then the oxygen becoming ozone 59 00:03:27,340 --> 00:03:30,359 and cutting out the ultraviolet radiation 60 00:03:30,360 --> 00:03:32,699 and allowing the plants and the animals 61 00:03:32,700 --> 00:03:34,900 to come out of the water for the first time. 62 00:03:36,700 --> 00:03:39,919 Plants, once confined to the seas, 63 00:03:39,920 --> 00:03:41,503 begin to spread inland. 64 00:03:42,754 --> 00:03:47,259 Ferns and the first trees start covering the land 65 00:03:47,260 --> 00:03:50,073 in vast often flooded forests. 66 00:03:51,890 --> 00:03:54,449 The Devonian's when you get a land environment 67 00:03:54,450 --> 00:03:56,989 that starts to look like something you might recognize. 68 00:03:56,990 --> 00:03:58,540 You go from nothing to forests. 69 00:03:59,570 --> 00:04:01,529 It was lush, it was lush and green. 70 00:04:01,530 --> 00:04:04,009 There weren't flowers yet but it was very green 71 00:04:04,010 --> 00:04:06,933 and very swampy and very alive. 72 00:04:07,990 --> 00:04:12,829 In the oceans, new kinds of fish dominate reefs 73 00:04:12,830 --> 00:04:15,253 larger than the world had ever seen. 74 00:04:19,550 --> 00:04:23,633 Placoderms like Dunkleosteus are snacking on each other. 75 00:04:25,599 --> 00:04:30,109 But other smaller fish are experimenting with lifestyles 76 00:04:30,110 --> 00:04:31,773 that will change everything. 77 00:04:36,570 --> 00:04:41,089 You have a variety of fish that actually are maneuvering 78 00:04:41,090 --> 00:04:42,579 their way around in shallow water 79 00:04:42,580 --> 00:04:46,719 and they have these globe-like fins that actually, 80 00:04:46,720 --> 00:04:47,999 if you look at the fossils of them, 81 00:04:48,000 --> 00:04:50,469 actually you can start to see the rays of fins 82 00:04:50,470 --> 00:04:53,709 actually have distinct bones and it's this lineage 83 00:04:53,710 --> 00:04:58,710 of fish that eventually evolves into amphibians. 84 00:05:02,030 --> 00:05:05,213 With four sturdy fins to prop themselves up on, 85 00:05:06,060 --> 00:05:10,773 these fish are now in prime position to snap up prey. 86 00:05:12,690 --> 00:05:14,823 And some of them, like Dipterus, 87 00:05:16,240 --> 00:05:18,520 develop not just rudimentary limbs 88 00:05:19,800 --> 00:05:22,263 but little air sacs off their tracheas. 89 00:05:24,330 --> 00:05:26,469 If the water was becoming stagnant, 90 00:05:26,470 --> 00:05:29,029 they could go to the top of the water 91 00:05:29,030 --> 00:05:31,873 and gulp air and get their oxygen that way. 92 00:05:33,250 --> 00:05:36,263 The first lung fish are born. 93 00:05:40,640 --> 00:05:43,300 Limbs and lungs are about to come in handy 94 00:05:45,050 --> 00:05:48,103 because the Devonian climate is getting erratic. 95 00:05:51,000 --> 00:05:53,439 Those mountains thrust up by the collision 96 00:05:53,440 --> 00:05:57,729 of Europe and America catch water evaporating 97 00:05:57,730 --> 00:06:02,170 off the seas creating the first massive rains on Earth 98 00:06:03,320 --> 00:06:06,209 and the first fresh water habitats 99 00:06:06,210 --> 00:06:08,113 for the world's fish to explore. 100 00:06:11,000 --> 00:06:13,649 You had wet periods when it was very cloudy 101 00:06:13,650 --> 00:06:15,579 and lots of rain and you had dry periods 102 00:06:15,580 --> 00:06:18,859 when the rain would fail and so it became a very good 103 00:06:18,860 --> 00:06:23,659 adaptation if you could get out of the water from one pond, 104 00:06:23,660 --> 00:06:26,803 drying up pond, and get over into another drying up pond. 105 00:06:29,070 --> 00:06:33,280 But Dipterus is still very much a fish. 106 00:06:33,281 --> 00:06:37,163 It's limbs can't support its weight completely out of water. 107 00:06:38,400 --> 00:06:41,199 For a long time, this was a sticking point 108 00:06:41,200 --> 00:06:42,863 in our evidence of evolution. 109 00:06:44,791 --> 00:06:48,039 There was just no transitional fossil 110 00:06:48,040 --> 00:06:49,653 of a fish that could walk. 111 00:06:54,340 --> 00:06:59,219 But in 2004 that all changed with the discovery 112 00:06:59,220 --> 00:07:03,184 of the famous Tiktaalik, our first tetrapod, 113 00:07:03,185 --> 00:07:06,033 or four-footed fossil. 114 00:07:08,770 --> 00:07:10,644 The way they found Tiktaalik was they said, 115 00:07:10,645 --> 00:07:13,556 "At this time period we should find a fossil 116 00:07:13,557 --> 00:07:16,466 "of an animal that's got pretty well-developed arm bones 117 00:07:16,467 --> 00:07:19,306 "and who looks like a fish but it has limbs 118 00:07:19,307 --> 00:07:21,866 "that are on their way to evolving into arms. 119 00:07:21,867 --> 00:07:22,860 "Let's see if we can go find it." 120 00:07:22,860 --> 00:07:23,693 And they did. 121 00:07:23,694 --> 00:07:25,939 It was one of those great point to the left field fence 122 00:07:25,940 --> 00:07:28,683 and hit the home run kind of moments in paleontology. 123 00:07:31,360 --> 00:07:34,023 Tiktaalik is basically a fish with feet. 124 00:07:36,170 --> 00:07:38,939 They gave rise to amphibians. 125 00:07:38,940 --> 00:07:42,033 And ultimately, to us. 126 00:07:46,840 --> 00:07:49,039 They had to go back in the water to stay wet 127 00:07:49,040 --> 00:07:51,049 and they had to go back in the water to lay their eggs 128 00:07:51,050 --> 00:07:53,789 but they were partially freed from life in the water 129 00:07:53,790 --> 00:07:56,723 and that's how life on the land for the vertebrates began. 130 00:07:58,770 --> 00:08:01,811 But as Tiktaalik was venturing onto land, 131 00:08:01,812 --> 00:08:04,569 planet Earth was about to experience 132 00:08:04,570 --> 00:08:07,874 its second period of very bad days. 133 00:08:07,875 --> 00:08:10,875 (suspenseful music) 134 00:08:14,460 --> 00:08:18,659 And the end of Devonian around 375 million years ago, 135 00:08:18,660 --> 00:08:20,545 there's another mass extinction. 136 00:08:20,546 --> 00:08:24,699 This one looks like it might be a multiple mass extinction 137 00:08:24,700 --> 00:08:28,110 meaning it was a longer term event 138 00:08:28,111 --> 00:08:33,111 that was made up of separate individual rapid events. 139 00:08:33,480 --> 00:08:36,709 Something is happening at very specific intervals 140 00:08:36,710 --> 00:08:38,959 which is making the coral reefs disappear, 141 00:08:38,960 --> 00:08:41,378 which is changing fish evolution, 142 00:08:41,379 --> 00:08:44,659 which is changing some of the things with shells 143 00:08:44,660 --> 00:08:46,410 that are living in the coral reefs. 144 00:08:51,760 --> 00:08:53,019 The jury is still out 145 00:08:53,020 --> 00:08:54,593 on what caused the extinction. 146 00:08:58,470 --> 00:09:01,339 But from the latest research it looks 147 00:09:01,340 --> 00:09:03,209 as though some of that new rather 148 00:09:03,210 --> 00:09:07,533 unsuspecting Devonian life is a primary culprit. 149 00:09:10,770 --> 00:09:14,539 It turns out all those trees covering the continents 150 00:09:14,540 --> 00:09:18,080 were pumping out oxygen at rates the world had never known 151 00:09:20,660 --> 00:09:24,013 while simultaneously soaking up carbon dioxide, 152 00:09:25,564 --> 00:09:28,883 cooling the world in a sort of reverse greenhouse effect. 153 00:09:31,780 --> 00:09:34,609 The byproducts of a forest and the byproducts 154 00:09:34,610 --> 00:09:36,606 of soil is that you have river discharge, 155 00:09:36,607 --> 00:09:38,999 you have submarine brown water discharge 156 00:09:39,000 --> 00:09:40,459 that's full of nutrients. 157 00:09:40,460 --> 00:09:41,729 They're gonna make a balloon 158 00:09:41,730 --> 00:09:45,089 and that's gonna chose the oxygen off for everybody else. 159 00:09:45,090 --> 00:09:46,909 What we think of as a coral reef is nothing 160 00:09:46,910 --> 00:09:48,763 compared to what they used to be. 161 00:09:50,980 --> 00:09:53,319 And to add insult to injury, 162 00:09:53,320 --> 00:09:56,909 recent evidence indicates the earth took it on the chin 163 00:09:56,910 --> 00:10:00,509 from an asteroid or other space rock large enough 164 00:10:00,510 --> 00:10:03,053 to seal the fate of many species. 165 00:10:04,810 --> 00:10:06,659 If you look at those layers, 166 00:10:06,660 --> 00:10:08,133 one finds evidence of impact. 167 00:10:09,017 --> 00:10:12,739 There are these little objects called microtektites. 168 00:10:12,740 --> 00:10:16,129 They are little drops of molten rock 169 00:10:16,130 --> 00:10:19,125 that were spewed out of the crater 170 00:10:19,126 --> 00:10:22,079 and they're transported around the world. 171 00:10:22,080 --> 00:10:24,999 And if you find a layer with microtektites, 172 00:10:25,000 --> 00:10:27,039 that means there was impact somewhere 173 00:10:27,040 --> 00:10:28,340 on the Earth at that time. 174 00:10:30,460 --> 00:10:32,169 Whatever the cause, 175 00:10:32,170 --> 00:10:34,619 the fossil record from the period reveals 176 00:10:34,620 --> 00:10:37,149 that over the course of millions of years, 177 00:10:37,150 --> 00:10:40,239 the mysterious catastrophe spelled bad news 178 00:10:40,240 --> 00:10:43,239 for 3/4 of the species on earth. 179 00:10:43,240 --> 00:10:45,299 Yes, it's a sad thing for the things that died 180 00:10:45,300 --> 00:10:48,299 but there are winners and losers in every mass extinction. 181 00:10:48,300 --> 00:10:50,539 Though the vast majority of fish 182 00:10:50,540 --> 00:10:53,693 in the sea were wiped out in the great Devonian extinction, 183 00:10:55,280 --> 00:10:59,483 the fish with feet planted them firmly on terra firma. 184 00:11:01,250 --> 00:11:04,333 The tetrapods were set on world domination. 185 00:11:05,920 --> 00:11:08,299 The great ages of amphibians, 186 00:11:08,300 --> 00:11:11,713 reptiles, and mammals lay ahead. 187 00:11:12,763 --> 00:11:16,430 (dramatic orchestral music)