1 00:00:01,920 --> 00:00:07,160 Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff, 2 00:00:07,240 --> 00:00:10,280 Speaker 1: Lorenvolk bum here with a classic episode from our former host, 3 00:00:10,360 --> 00:00:13,440 Speaker 1: Christian Sagar. This one is near and dear to me. 4 00:00:14,040 --> 00:00:17,920 Speaker 1: Our topic for the day is why the Tyrannosaurus Rex 5 00:00:18,120 --> 00:00:23,919 Speaker 1: have such tiny arms? A brain Stuff it's Christian Sagar. 6 00:00:24,160 --> 00:00:27,680 Speaker 1: With a name that literally means tyrant lizard king, you'd 7 00:00:27,680 --> 00:00:31,000 Speaker 1: assume that Tyrannosaurus rex would get a bit more respect, 8 00:00:31,320 --> 00:00:35,159 Speaker 1: but the giant predators disproportionately small arms have been the 9 00:00:35,200 --> 00:00:40,400 Speaker 1: subject of ridicule for decades. They are also a scientific puzzle. 10 00:00:40,680 --> 00:00:43,800 Speaker 1: More than one hundred years after discovery of this species, 11 00:00:44,120 --> 00:00:47,800 Speaker 1: experts still don't know why a huge animal, one that 12 00:00:47,840 --> 00:00:51,880 Speaker 1: could reach links of forty feet or twelve meters or more, 13 00:00:52,360 --> 00:00:56,360 Speaker 1: had four limbs that weren't much longer than an adult humans. 14 00:00:56,840 --> 00:01:00,440 Speaker 1: If the arms were limp muscle free pegs, it'd easy 15 00:01:00,480 --> 00:01:03,880 Speaker 1: to assume that they serve no purpose. However, the evidence 16 00:01:04,000 --> 00:01:07,440 Speaker 1: hints at a more complicated story. A few studies have 17 00:01:07,560 --> 00:01:10,720 Speaker 1: argued that, judging by the muscle scars left behind on 18 00:01:10,880 --> 00:01:15,319 Speaker 1: t rex limb bones, a full grown dinosaur could curl 19 00:01:15,640 --> 00:01:18,480 Speaker 1: more than two hundred and twenty pounds or one hundred 20 00:01:18,959 --> 00:01:22,880 Speaker 1: rams with each one of their biceps. Then again, this 21 00:01:22,959 --> 00:01:26,920 Speaker 1: isn't as impressive as it sounds. Thomas ore Holtz, a 22 00:01:27,040 --> 00:01:31,280 Speaker 1: vertebrate paleontologist at the University of Maryland, tells us that 23 00:01:31,360 --> 00:01:35,440 Speaker 1: some people like to overrate tyrannosaurus is upper body strength. 24 00:01:35,800 --> 00:01:39,560 Speaker 1: That figure from before only translates to about one point 25 00:01:39,600 --> 00:01:43,280 Speaker 1: to five per cent of the dinosaurs total body weight, 26 00:01:43,600 --> 00:01:46,440 Speaker 1: which may have been in the ballpark of around eight 27 00:01:46,480 --> 00:01:51,120 Speaker 1: tons or eight thousand kilograms. Holtz says that's like a 28 00:01:51,200 --> 00:01:55,400 Speaker 1: two hundred pound or nine man being proud of the 29 00:01:55,440 --> 00:02:00,000 Speaker 1: ability to curl two point five pounds or one kilogram. 30 00:02:00,280 --> 00:02:04,200 Speaker 1: On these grounds, A few experts have concluded that Tyrannosaurus's 31 00:02:04,440 --> 00:02:09,639 Speaker 1: arms were either functionless or seldom used, but not all 32 00:02:09,720 --> 00:02:14,240 Speaker 1: paleontologists by this idea. For his money, Kenneth Carpenter of 33 00:02:14,360 --> 00:02:19,280 Speaker 1: Utah State University thinks the little limbs made great hunting tools. 34 00:02:19,320 --> 00:02:23,600 Speaker 1: In two thousand eight, he and fellow paleontologist Christine Lipkin 35 00:02:23,960 --> 00:02:29,600 Speaker 1: compared the five Tyrannosaurus rex wishbones or ferculars that were 36 00:02:29,680 --> 00:02:33,000 Speaker 1: known to science at the time. Shaped like a giant boomerang, 37 00:02:33,120 --> 00:02:37,000 Speaker 1: the fercular sits between the shoulder blades. Three of the 38 00:02:37,080 --> 00:02:41,839 Speaker 1: five wishbones that Carpenter and Lipkin studied show telltale signs 39 00:02:41,880 --> 00:02:45,960 Speaker 1: of injury. Among these were stress fractures, which must have 40 00:02:46,120 --> 00:02:49,320 Speaker 1: re healed in life. So what does this mean? While 41 00:02:49,360 --> 00:02:52,800 Speaker 1: according to Carpenter, the four limbs were subjected to a 42 00:02:53,000 --> 00:02:58,840 Speaker 1: great deal of repetitive stress, which was not uniform or steady. Instead, 43 00:02:58,919 --> 00:03:03,079 Speaker 1: there were moments of x e straordinarily great force applied 44 00:03:03,240 --> 00:03:06,519 Speaker 1: to the arms. The most likely explanation is that t 45 00:03:06,760 --> 00:03:10,720 Speaker 1: Rex used its four limbs to grab hold of large 46 00:03:10,720 --> 00:03:16,519 Speaker 1: struggling prey. A plus sized thrashing victim could easily fracture 47 00:03:16,520 --> 00:03:20,440 Speaker 1: the carnivores wishbone or at least tear a few arm 48 00:03:20,560 --> 00:03:24,360 Speaker 1: muscles loose. Other ideas about the purpose of t rex 49 00:03:24,480 --> 00:03:28,080 Speaker 1: arms have nothing to do with subduing victims. One school 50 00:03:28,080 --> 00:03:31,760 Speaker 1: of thought involves naptime. Perhaps after a good night's sleep, 51 00:03:31,880 --> 00:03:35,840 Speaker 1: Torannosaurus used those arms to push itself up off the ground, 52 00:03:36,440 --> 00:03:41,120 Speaker 1: or maybe they had a sexier function. Henry Fairfield Osborne, 53 00:03:41,120 --> 00:03:44,800 Speaker 1: the paleontologists who named this species back in nineteen o five, 54 00:03:45,120 --> 00:03:48,960 Speaker 1: believed that males used their four limbs to grab hold 55 00:03:49,160 --> 00:03:52,640 Speaker 1: of their mates as Holts and others have admitted there 56 00:03:52,640 --> 00:03:56,800 Speaker 1: simply isn't enough evidence at this time to conclusively refute 57 00:03:56,960 --> 00:04:01,120 Speaker 1: or verify any of these notions. Much is often the 58 00:04:01,200 --> 00:04:08,480 Speaker 1: nature of paleontology. Today's episode was written by Mark Fancini 59 00:04:08,520 --> 00:04:11,440 Speaker 1: and produced by Dylan Fagan and Tyler Clang. For more 60 00:04:11,440 --> 00:04:13,200 Speaker 1: in this and lots of other topics, visit how stuff 61 00:04:13,200 --> 00:04:15,960 Speaker 1: works dot com. Brain Stuff is a production of iHeart Radio. 62 00:04:16,160 --> 00:04:18,360 Speaker 1: For more podcasts in my heart Radio, visit the iHeart 63 00:04:18,400 --> 00:04:21,040 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 64 00:04:21,080 --> 00:04:21,719 Speaker 1: favorite shows.