1 00:00:03,279 --> 00:00:05,640 Speaker 1: Welcome to Stuff to Blow Your Mind, a production of 2 00:00:05,640 --> 00:00:10,600 Speaker 1: I Heart Radio. Hi, my name is Joe McCormick, and 3 00:00:10,680 --> 00:00:13,960 Speaker 1: this is the Artifact, a short form series from Stuff 4 00:00:14,040 --> 00:00:17,560 Speaker 1: to Blow Your Mind, focusing on particular objects, ideas, and 5 00:00:17,680 --> 00:00:23,800 Speaker 1: moments in time. Despite what you might see in some 6 00:00:23,880 --> 00:00:28,000 Speaker 1: classic picture books, not all species of dinosaurs lived together 7 00:00:28,160 --> 00:00:31,120 Speaker 1: at the same time. You might have seen an illustration 8 00:00:31,160 --> 00:00:34,520 Speaker 1: where a tyrannosaurus is opening its jaws to clamp down 9 00:00:34,520 --> 00:00:37,839 Speaker 1: on the neck of a lone stegosaurus while the stegosaurus 10 00:00:37,960 --> 00:00:41,159 Speaker 1: raises the end of its spiked tail and defense. But 11 00:00:41,280 --> 00:00:44,400 Speaker 1: this never happened. We know it never happened because the 12 00:00:44,400 --> 00:00:48,400 Speaker 1: Tyrannosaurus lived about sixty six million years ago and the 13 00:00:48,400 --> 00:00:51,920 Speaker 1: Stegosaurus genus lived a hundred and fifty million years ago. 14 00:00:52,640 --> 00:00:56,080 Speaker 1: The time between them was more than eighty million years, 15 00:00:56,240 --> 00:00:59,240 Speaker 1: which is actually greater than the time between the extinction 16 00:00:59,280 --> 00:01:03,080 Speaker 1: of the non avian dinosaurs and us. If you show 17 00:01:03,080 --> 00:01:05,920 Speaker 1: a t rex fighting a stegosaurus, you might as well 18 00:01:05,920 --> 00:01:10,000 Speaker 1: show a group of humans hunting at triceratops. Just like us, 19 00:01:10,120 --> 00:01:15,120 Speaker 1: dinosaurs lived within particular ecological communities, groups of organisms that 20 00:01:15,200 --> 00:01:18,760 Speaker 1: all occupied the same time and place, and when you 21 00:01:18,800 --> 00:01:22,959 Speaker 1: look at fossils in terms of individual communities, interesting questions 22 00:01:23,000 --> 00:01:26,520 Speaker 1: can arise. This week, I came across a study published 23 00:01:26,520 --> 00:01:30,320 Speaker 1: in the journal Science in February by a group of 24 00:01:30,319 --> 00:01:35,840 Speaker 1: paleoecologists named Katlin Schroeder, S, Kathleen Lyons, and FELICEA. A. Smith, 25 00:01:36,200 --> 00:01:40,280 Speaker 1: which discussed a potentially mysterious gap that emerges when you 26 00:01:40,319 --> 00:01:43,400 Speaker 1: try to put together a picture of these dinosaur communities 27 00:01:43,440 --> 00:01:47,360 Speaker 1: from the fossil record. Most of the time these communities 28 00:01:47,400 --> 00:01:52,960 Speaker 1: are missing something medium sized carnivores. This gap in medium 29 00:01:53,000 --> 00:01:58,120 Speaker 1: sized animals seems specific to dinosaurs and carnivorous dinosaurs in particular, 30 00:01:58,240 --> 00:02:01,200 Speaker 1: rather than something that is general really observed in nature. 31 00:02:01,800 --> 00:02:03,880 Speaker 1: For example, if you look at the carnivores that live 32 00:02:03,920 --> 00:02:07,440 Speaker 1: on the African savannah today, you'll find small carnivores like 33 00:02:07,480 --> 00:02:11,240 Speaker 1: the mongoose, large carnivores like the lion, and in between 34 00:02:11,400 --> 00:02:15,040 Speaker 1: plenty of medium sized carnivores like the wild dog. The 35 00:02:15,160 --> 00:02:18,399 Speaker 1: environment allows niches for meat eaters of all these sizes 36 00:02:18,440 --> 00:02:21,640 Speaker 1: because each can evolve to specialize in prey that's best 37 00:02:21,720 --> 00:02:24,800 Speaker 1: suited for its body mass. But when it comes to 38 00:02:24,840 --> 00:02:28,560 Speaker 1: communities of dinosaurs, the distribution often appears to have this 39 00:02:28,639 --> 00:02:32,000 Speaker 1: whole In the middle, there were giant predators, the ones 40 00:02:32,040 --> 00:02:35,680 Speaker 1: we know very well, the mega therapods like Terrannosaurus rex. 41 00:02:36,240 --> 00:02:39,800 Speaker 1: The class known as megatherapods includes any therapod predator that 42 00:02:39,840 --> 00:02:42,960 Speaker 1: grew to over a thousand kilograms, and there were some 43 00:02:43,000 --> 00:02:46,919 Speaker 1: small predators as well with body masses under one kilograms, 44 00:02:47,400 --> 00:02:51,040 Speaker 1: but there was often very little in between. These communities 45 00:02:51,080 --> 00:02:54,840 Speaker 1: mostly didn't have predators that were over a hundred kilograms 46 00:02:54,960 --> 00:02:58,520 Speaker 1: but under a thousand. To use a comparison cited in 47 00:02:58,600 --> 00:03:02,680 Speaker 1: the study itself, quote, if the modern mammal carnivore assemblage 48 00:03:02,680 --> 00:03:06,360 Speaker 1: of the Krueger National Park were similarly structured, there would 49 00:03:06,400 --> 00:03:09,880 Speaker 1: be no carnivores between the size of an African lion 50 00:03:10,200 --> 00:03:13,480 Speaker 1: at a hundred nine rams and a bat eared fox 51 00:03:13,639 --> 00:03:17,600 Speaker 1: at four kilograms. So what accounts for the dinosaur gap? 52 00:03:20,600 --> 00:03:23,120 Speaker 1: When there's an apparent gap in the fossil record, there's 53 00:03:23,160 --> 00:03:26,880 Speaker 1: always a possibility that what paleontologists are seeing is merely 54 00:03:26,919 --> 00:03:31,320 Speaker 1: a bias in the fossilization process. Most of the animals 55 00:03:31,320 --> 00:03:35,440 Speaker 1: that live and die never become fossils. Fossilization is a 56 00:03:35,480 --> 00:03:39,880 Speaker 1: special process that only takes place under unique conditions, for example, 57 00:03:40,080 --> 00:03:43,440 Speaker 1: when the bones are rapidly buried after the animal's death. 58 00:03:44,040 --> 00:03:46,160 Speaker 1: This is much more likely to happen in a wet 59 00:03:46,280 --> 00:03:48,840 Speaker 1: environment like a sea floor, which is why we have 60 00:03:48,960 --> 00:03:52,520 Speaker 1: far more fossils of prehistoric marine organisms than we do 61 00:03:52,560 --> 00:03:55,600 Speaker 1: of land animals. And when we do have the fossils 62 00:03:55,600 --> 00:03:58,960 Speaker 1: of a land animal, it's often because their bones somehow 63 00:03:59,080 --> 00:04:02,000 Speaker 1: fell into a water source or we're covered by a flood. 64 00:04:02,400 --> 00:04:04,480 Speaker 1: But shrowd to read all in their paper argue for 65 00:04:04,520 --> 00:04:08,480 Speaker 1: a different explanation. After they examined forty three communities of 66 00:04:08,520 --> 00:04:12,119 Speaker 1: dinosaurs across a hundred and thirty six million years, they 67 00:04:12,120 --> 00:04:15,680 Speaker 1: concluded that the meso carnivore gap is real, and the 68 00:04:15,760 --> 00:04:20,239 Speaker 1: explanation has to do with how dinosaurs reproduced and grew. 69 00:04:21,360 --> 00:04:25,400 Speaker 1: The largest therapod predators were gigantic once they reached full size. 70 00:04:25,839 --> 00:04:28,880 Speaker 1: An adult terinosaurs Rex probably grew to more than twelve 71 00:04:28,960 --> 00:04:32,200 Speaker 1: meters in length and weighed somewhere between four thousand and 72 00:04:32,279 --> 00:04:35,599 Speaker 1: seven thousand kilograms. They're often compared to the size of 73 00:04:35,680 --> 00:04:39,039 Speaker 1: large vehicles, but there's a fact that limits how big 74 00:04:39,080 --> 00:04:42,040 Speaker 1: the offspring of even the biggest dinosaurs could be when 75 00:04:42,080 --> 00:04:49,359 Speaker 1: they entered the environment. Dinosaurs are oviparous, they hatch from eggs. Mammals, 76 00:04:49,440 --> 00:04:52,400 Speaker 1: on the other hand, are viviporous, giving birth to live young, 77 00:04:52,720 --> 00:04:56,440 Speaker 1: and the newborns could be pretty stout. African elephant calves 78 00:04:56,440 --> 00:04:59,520 Speaker 1: are sometimes already over a hundred kilograms at the time 79 00:04:59,520 --> 00:05:03,040 Speaker 1: they're born. This gives those calves a leg up on survival, 80 00:05:03,120 --> 00:05:06,880 Speaker 1: but it also comes with biological costs. Mammals usually have 81 00:05:07,040 --> 00:05:10,560 Speaker 1: fewer offspring than oviporous species, and they have to invest 82 00:05:10,680 --> 00:05:14,520 Speaker 1: more resources into each one. An African elephant mother is 83 00:05:14,560 --> 00:05:17,839 Speaker 1: pregnant with each calf for almost two years, and even 84 00:05:17,880 --> 00:05:21,600 Speaker 1: after the calf is born, it's been several more years nursing. 85 00:05:22,160 --> 00:05:25,040 Speaker 1: But while egg laying species don't have these problems, there 86 00:05:25,040 --> 00:05:29,200 Speaker 1: are also drawbacks to egg based reproduction. For example, there 87 00:05:29,240 --> 00:05:33,680 Speaker 1: are harsh physical constraints on the size of eggs. The 88 00:05:33,760 --> 00:05:35,680 Speaker 1: shell of an egg has to be thin enough to 89 00:05:35,720 --> 00:05:39,600 Speaker 1: allow the permeation of gas so oxygen can get inside 90 00:05:39,600 --> 00:05:42,720 Speaker 1: and reach the developing embryo, and the shell also has 91 00:05:42,760 --> 00:05:44,880 Speaker 1: to be thin enough to allow the hatchling to break 92 00:05:44,920 --> 00:05:49,160 Speaker 1: out once it reaches maturity. But as eggs increase in size, 93 00:05:49,560 --> 00:05:53,440 Speaker 1: thin shells become less and less tenable. A huge egg 94 00:05:53,480 --> 00:05:56,680 Speaker 1: with a wafer like shell would break too easily. As 95 00:05:56,720 --> 00:05:59,960 Speaker 1: a result, even gigantic dinosaurs would have to lay pretty 96 00:06:00,040 --> 00:06:03,919 Speaker 1: small eggs shredder at all. Right. That oviparity meant even 97 00:06:03,960 --> 00:06:08,360 Speaker 1: the largest dinosaur species were limited to about fifteen kilograms, 98 00:06:08,480 --> 00:06:11,240 Speaker 1: which is roughly about thirty three pounds at the time 99 00:06:11,320 --> 00:06:14,120 Speaker 1: that they hatched. No matter how big the adult, the 100 00:06:14,120 --> 00:06:16,920 Speaker 1: new hatchlings were never going to be any bigger than 101 00:06:16,960 --> 00:06:21,159 Speaker 1: your average Welsh corky. A freshly hatched Tyrannosaurus rex was 102 00:06:21,200 --> 00:06:24,240 Speaker 1: probably about the size of a house cat. So these 103 00:06:24,279 --> 00:06:28,680 Speaker 1: mega theropods started very small, grew enormous in adulthood, and 104 00:06:28,760 --> 00:06:31,279 Speaker 1: had a lot of eating and growing to do along 105 00:06:31,279 --> 00:06:35,200 Speaker 1: the way, and there were lots of them. Ultimately, this 106 00:06:35,279 --> 00:06:38,760 Speaker 1: is the explanation offered by the authors of paper for 107 00:06:38,760 --> 00:06:42,560 Speaker 1: the meso carnivorre gap. The gap was filled by growing 108 00:06:42,720 --> 00:06:46,560 Speaker 1: mega therapods. In other words, these communities did have their 109 00:06:46,600 --> 00:06:51,040 Speaker 1: own medium sized carnivores, but they weren't separate species. They 110 00:06:51,040 --> 00:06:56,080 Speaker 1: were the rampaging juveniles of giant megatherapod predators. The young 111 00:06:56,240 --> 00:06:59,800 Speaker 1: functioned in the community almost as a species of their own, 112 00:07:00,520 --> 00:07:03,840 Speaker 1: and by functioning like different species in their juvenile phases. 113 00:07:03,920 --> 00:07:08,560 Speaker 1: Mega theropods limited species diversity. There's just less room in 114 00:07:08,600 --> 00:07:12,240 Speaker 1: the environment for a predator that reaches three ds as 115 00:07:12,280 --> 00:07:15,840 Speaker 1: an adult if there are lots of three t rex 116 00:07:15,920 --> 00:07:22,560 Speaker 1: teenagers running around competing for the same prey. Tune into 117 00:07:22,560 --> 00:07:25,720 Speaker 1: new editions of the Artifact every Wednesday, hosted by either 118 00:07:25,840 --> 00:07:28,960 Speaker 1: Robert or myself. As always, you can email us at 119 00:07:29,160 --> 00:07:40,360 Speaker 1: contact at stuff to Blow your Mind dot com. Stuff 120 00:07:40,400 --> 00:07:42,600 Speaker 1: to Blow Your Mind is production of I Heart Radio. 121 00:07:42,960 --> 00:07:45,080 Speaker 1: For more podcasts for my heart Radio, visit the i 122 00:07:45,120 --> 00:07:47,960 Speaker 1: heart Radio app, Apple Podcasts, or wherever you listen to 123 00:07:47,960 --> 00:07:48,800 Speaker 1: your favorite shows.