WEBVTT - Dimetrodon Wasn't a Dinosaur -- So What Was It? 0:00:01.910 --> 0:00:07.570 Welcome to BrainStuff, a production of iHeart Podcasts. Hey BrainStuff, 0:00:07.670 --> 0:00:13.050 Lauren Vogelbaum here. Of course, all prehistoric fossils are incredible 0:00:13.070 --> 0:00:15.890 when you think about them, but some are more striking 0:00:15.950 --> 0:00:19.300 than others due to sheer size or features that remind 0:00:19.340 --> 0:00:22.560 you you're looking at something from what was, in all practicality, 0:00:22.579 --> 0:00:27.760 a different world. The Dimetrodon is one of those. The 0:00:27.800 --> 0:00:31.460 biggest species were big, over 15 feet from nose to tail, 0:00:31.540 --> 0:00:34.730 that's about 4.5 meters, and they might have weighed some 0:00:34.729 --> 0:00:39.950 550 pounds or 250 kilos. It walked on four sort 0:00:39.990 --> 0:00:43.030 of stubby legs and had a long, blunt skull that 0:00:43.130 --> 0:00:45.970 reminds me of a bull terrier. Or a bull terrier 0:00:46.010 --> 0:00:50.210 with really scary teeth. And standing up over its back 0:00:50.430 --> 0:00:55.029 was an impressive spiny fan that towered some 5 feet 0:00:55.190 --> 0:00:59.080 or 1.5 meters at its center. That makes this animal 0:00:59.100 --> 0:01:04.040 about the length and height of a mid-sized sedan. Dimetrodon 0:01:04.080 --> 0:01:06.760 was a prehistoric predator that lived in what's now North 0:01:06.800 --> 0:01:11.980 America and Europe between about 295 and 275 million years ago. 0:01:13.060 --> 0:01:15.340 Some species would have been smaller, about a third of 0:01:15.380 --> 0:01:18.900 the size of the buddies mentioned above. there are around 0:01:18.900 --> 0:01:23.400 14 recognized species, grouped partially because of that distinctive sale. 0:01:24.660 --> 0:01:28.190 But don't ignore the rest of the animal. Dimetrodon's teeth 0:01:28.290 --> 0:01:32.930 and skull openings helped paleontologists recognize this dramatic beast for 0:01:32.970 --> 0:01:36.130 what it was, a member of the same animal clade 0:01:36.170 --> 0:01:40.560 that gave rise to mammals like us. That's right, Dimetrodon 0:01:40.819 --> 0:01:45.130 was not a dinosaur. For the article this episode is 0:01:45.170 --> 0:01:48.970 based on, back in 2022, HowStuffWorks spoke via email with 0:01:49.030 --> 0:01:53.930 Caroline Abbott, a paleontologist with the University of Chicago. She explained, 0:01:54.470 --> 0:01:58.630 Dimetrodon is what we call a synapsid. About 310 million 0:01:58.670 --> 0:02:01.860 years ago, the first amniotes, that is, vertebrates able to 0:02:01.890 --> 0:02:05.560 lay eggs on dry land, split into these two separate lineages, 0:02:05.780 --> 0:02:08.760 the synapsids and the reptiles, and the two groups have 0:02:08.800 --> 0:02:12.980 had separate evolutionary histories ever since. Dimetrodon is one of 0:02:13.020 --> 0:02:18.079 the earlier synapsids. The only synapsids that are still around 0:02:18.120 --> 0:02:22.760 today are mammals. The first true mammals wouldn't arise until 0:02:22.820 --> 0:02:27.760 sometime between 208 and 178 million years ago, long after 0:02:27.780 --> 0:02:32.060 the Dimetrodon had died out. Still, being a synapsid, the 0:02:32.120 --> 0:02:35.500 old finback had closer evolutionary ties to humans than it 0:02:35.560 --> 0:02:40.560 did to any modern reptiles, or to the dinosaurs. So 0:02:40.639 --> 0:02:43.020 how can we tell that the Dimetrodon was a synapsid? 0:02:43.680 --> 0:02:46.559 There were a few clues that tipped fossil hunters off 0:02:46.720 --> 0:02:51.250 after the creature was discovered in the 1800s. Hustaforks also 0:02:51.310 --> 0:02:55.070 spoke via email with Hans Seuss, curator of vertebrate paleontology 0:02:55.110 --> 0:02:58.590 at the Smithsonian National Museum of Natural History. Seuss has 0:02:58.610 --> 0:03:01.450 since passed away, but he said at the time, The 0:03:01.490 --> 0:03:04.980 key feature of all animals in the evolutionary lineage leading 0:03:05.040 --> 0:03:08.180 to mammals is the presence of a large opening behind 0:03:08.240 --> 0:03:12.090 the eye socket on the skull. This feature becomes much 0:03:12.310 --> 0:03:16.609 larger in more advanced species and houses the jaw-closing muscles. 0:03:17.330 --> 0:03:19.389 You can feel those muscles if you put your fingers 0:03:19.450 --> 0:03:24.620 on your temples and clench your jaws. Also, just like 0:03:24.660 --> 0:03:28.520 a lot of mammals, Dimetrodon was a heterodont. That means 0:03:28.540 --> 0:03:32.380 that the creature's teeth did not all look the same. Rather, 0:03:32.540 --> 0:03:35.120 its pearly whites came in a variety of shapes and 0:03:35.160 --> 0:03:40.290 held a number of functions. Dimetrodon had, Seuss said, Incisor-like 0:03:40.350 --> 0:03:43.790 front teeth, a large canine or eye tooth, and smaller 0:03:43.830 --> 0:03:49.010 teeth behind the canine. Some species of Dimetrodon even evolved 0:03:49.090 --> 0:03:52.520 serrated teeth to help them take down increasingly large prey, 0:03:53.080 --> 0:03:55.500 and they did it about 40 million years earlier than 0:03:55.580 --> 0:04:02.140 predatory dinosaurs. But okay, about that sale. Backbones, or vertebrae, 0:04:02.480 --> 0:04:05.930 are topped with knobby columns of bone called neural spines. 0:04:06.720 --> 0:04:09.630 These are oriented vertically in animals that walk around on 0:04:09.670 --> 0:04:14.330 all fours. In humans, the neural spines point backward. They're 0:04:14.370 --> 0:04:17.349 the little bumps you can feel protruding underneath the skin 0:04:17.410 --> 0:04:19.290 when you rub the back of your neck or your 0:04:19.330 --> 0:04:24.919 spinal column. Dimetrodon's iconic sail was made up of extremely long, 0:04:25.279 --> 0:04:29.480 rod-like neural spines. The tallest ones occurred in the middle 0:04:29.540 --> 0:04:32.719 of the creature's back, between the shoulder and hips, giving 0:04:32.779 --> 0:04:34.980 the sail as a whole sort of a bell curve. 0:04:36.360 --> 0:04:38.359 And if you want to know what the sail was for, 0:04:38.920 --> 0:04:43.279 join the club. Seuss said, Nobody really knows because there 0:04:43.320 --> 0:04:46.120 are no living animals with such sails that could be 0:04:46.230 --> 0:04:51.210 used for comparison. Today's mammals, by and large, keep a 0:04:51.290 --> 0:04:55.890 constant internal body temperature. It's possible that Dimetrodon lacked this 0:04:55.950 --> 0:04:58.630 ability and would have had to rely on its environment 0:04:58.750 --> 0:05:02.540 to warm itself up or cool itself down. Abbott said, 0:05:03.240 --> 0:05:06.419 Having tall neural spines with tissue and blood vessels in 0:05:06.460 --> 0:05:09.440 between would provide a lot of surface area to help 0:05:09.500 --> 0:05:13.640 with thermoregulation, or how an animal maintains ideal body temperatures. 0:05:14.420 --> 0:05:17.849 The sale of Dimetrodon might have been essentially a giant 0:05:17.890 --> 0:05:20.950 solar panel that allowed it to get going earlier and 0:05:21.010 --> 0:05:23.890 keep moving longer in the day. That's a huge leg 0:05:23.930 --> 0:05:28.550 up if you're a predator. But some researchers have their doubts. 0:05:29.380 --> 0:05:32.800 Dimetrodon lived in the early part of Earth's Permian period, 0:05:33.040 --> 0:05:37.520 which lasted from around 298 to 251 million years ago. 0:05:38.660 --> 0:05:41.190 One of its closest relatives from around the same time 0:05:41.320 --> 0:05:44.990 was another carnivore with a similar build overall, except it 0:05:45.089 --> 0:05:48.370 lacked a massive sail on its back. So why would 0:05:48.430 --> 0:05:50.950 one of these creatures need a solar panel if the 0:05:51.010 --> 0:05:55.010 other got along fine without it? Sexual selection could be 0:05:55.070 --> 0:05:58.880 the X factor here. If the sail wasn't used for thermoregulation, 0:05:59.080 --> 0:06:02.790 then maybe it acted as a prehistoric babe magnet. Abbott 0:06:02.850 --> 0:06:07.150 said that sometimes, quote, ornamental structures evolve due to mate preferences, 0:06:07.430 --> 0:06:10.790 such as in bright bird feathers or deer antlers. In 0:06:10.810 --> 0:06:13.750 that sense, a sail for sexual display would have come 0:06:13.810 --> 0:06:17.480 about because other Dimetrodon found it appealing for mate choice. 0:06:19.660 --> 0:06:22.460 Whatever the structure's real purpose may have been, this much 0:06:22.500 --> 0:06:27.800 we know. It wasn't unique to Dimetrodon. A vegetarian synapsid 0:06:27.839 --> 0:06:29.980 from the same era had one, as so did a 0:06:30.080 --> 0:06:35.339 prehistoric amphibian. And long, long after all those critters went extinct, 0:06:35.740 --> 0:06:40.669 a few dinosaurs independently evolved the same basic feature. Far 0:06:40.700 --> 0:06:43.469 and away, the most famous sail-backed dinosaur of them all 0:06:43.770 --> 0:06:48.270 is Spinosaurus. It lived in the Cretaceous period some 97 0:06:48.270 --> 0:06:51.710 million years ago. With an estimated length of almost 50 0:06:51.710 --> 0:06:55.650 feet or 15 meters, this was quite possibly the longest 0:06:55.710 --> 0:06:59.290 carnivore ever walk on dry land, although it might have 0:06:59.330 --> 0:07:04.110 preferred hunting in rivers. But again, since Dimetrodon was a 0:07:04.190 --> 0:07:07.610 forerunner of mammals, it had nothing whatsoever to do with 0:07:07.630 --> 0:07:12.790 the likes of Spinosaurus or T-Rex or Triceratops. It probably 0:07:12.830 --> 0:07:15.790 gets lumped in there because of toy companies mislabeling it 0:07:15.870 --> 0:07:20.770 in playsets and bags of plastic figurines. And Hollywood is 0:07:20.810 --> 0:07:24.210 no help. Fantasia and The Land Before Time both have 0:07:24.250 --> 0:07:30.670 this Permian synapsid brushing shoulders with actual dinosaurs. Again, Dimetrodon 0:07:30.710 --> 0:07:33.340 died out tens of millions of years before the first 0:07:33.380 --> 0:07:44.440 dinosaurs even showed up. Abbott said, Unlike the bipedal Spinosaurus, 0:07:44.540 --> 0:07:47.940 Dimetrodon walked around on four legs. The fossil evidence has 0:07:47.990 --> 0:07:51.770 made that clear. other aspects of its appearance and behavior 0:07:51.990 --> 0:07:56.739 are more mysterious. Abbott said, We've never found skin impressions 0:07:56.860 --> 0:08:00.820 associated with the bones of Dimetrodon, but the animal more 0:08:00.860 --> 0:08:04.940 than likely had some scales and no hair, both because 0:08:04.980 --> 0:08:07.180 of what we vaguely know of when hair may have 0:08:07.220 --> 0:08:14.050 evolved in synapsids and indirect evidence from trackways. Scientists have 0:08:14.070 --> 0:08:17.910 described the fossilized impressions of the feet and underbellies from 0:08:18.090 --> 0:08:21.460 early Permian synapsids thought to be, or at least be 0:08:21.520 --> 0:08:26.780 akin to, Dimetrodon. Whatever they were, these animals left behind 0:08:26.800 --> 0:08:30.980 the traces of prominent stomach scales. Some of these tracks 0:08:31.060 --> 0:08:34.250 found in Germany seem to indicate that these animals socialized, 0:08:34.650 --> 0:08:37.309 walking and resting next to each other as they basked 0:08:37.350 --> 0:08:41.450 in the sun and cooled down in shallow pools. As 0:08:41.510 --> 0:08:44.370 for synapsid hair, we know it must have evolved by 0:08:44.370 --> 0:08:48.080 164 million years ago. That's around 10 to 20 million 0:08:48.120 --> 0:08:52.120 years after the last known Dimetrodon. That's when the first 0:08:52.240 --> 0:08:55.260 definitive mammal hair imprints show up in the fossil record. 0:08:55.900 --> 0:09:01.470 In coprolites. That is, in fossilized poop. Any aspiring paleo 0:09:01.530 --> 0:09:09.130 artists will want to keep this in mind. Today's episode 0:09:09.190 --> 0:09:11.710 is based on the article, Think Dimetrodon Was a Dinosaur? 0:09:11.970 --> 0:09:16.240 Think Again, on HowStuffWorks.com, written by Mark Mancini. BrainStuff is 0:09:16.250 --> 0:09:19.520 a production of iHeart Podcasts in partnership with HowStuffWorks.com and 0:09:19.559 --> 0:09:23.100 is produced by Tyler Klang. For more shows from iHeart Podcasts, 0:09:23.280 --> 0:09:26.640 visit the iHeart Radio app, Apple Podcasts, or wherever you 0:09:26.679 --> 0:09:27.890 listen to your favorite shows.