WEBVTT - Why Do Turtles Have Shells? 0:00:02.040 --> 0:00:07.040 Welcome to brain stuff. From how stuff works, Hey, brain stuff, 0:00:07.120 --> 0:00:09.760 Lauren boge obamb here. Many of us have seen a 0:00:09.800 --> 0:00:13.000 turtle tucking itself into its protective shell, pulling in not 0:00:13.080 --> 0:00:15.440 only its four legs, but its head and tail as well. 0:00:16.040 --> 0:00:19.400 But while its shell shields a turtle's tender innards, it 0:00:19.480 --> 0:00:22.840 wasn't originally designed for that purpose, as an international group 0:00:22.840 --> 0:00:26.160 of scientists has found. Instead, they say the turtle shell 0:00:26.280 --> 0:00:30.280 most likely began as a digging tool. Tyler Lison, who 0:00:30.400 --> 0:00:32.720 is the lead author of the studying question and a 0:00:32.760 --> 0:00:36.200 paleontologist at the Denver Museum of Nature and Science, writes 0:00:36.280 --> 0:00:40.800 that when turtles first began developing shells a major evolutionary transition. 0:00:41.120 --> 0:00:44.920 The process included a broadening of the ribs. Broadened ribs 0:00:44.920 --> 0:00:48.559 made the turtles thoraxic region, or chest, more rigid. But 0:00:48.680 --> 0:00:51.360 the puzzling thing is that a rigid chest means it's 0:00:51.400 --> 0:00:54.600 harder for the animal to breathe easily or move swiftly, 0:00:55.080 --> 0:00:59.520 hardly changes that appear to enhance protective capabilities. But that's 0:00:59.560 --> 0:01:02.960 because initially, turtle shells made of more than fifty fused 0:01:03.000 --> 0:01:06.440 bones and their broad ribs were developed not for protection 0:01:06.680 --> 0:01:08.800 but to lend stability to the turtles so it could 0:01:08.840 --> 0:01:12.640 forcefully dig with its forelimbs. The researchers found being able 0:01:12.680 --> 0:01:14.840 to dig into the ground for food and shelter, they 0:01:14.880 --> 0:01:18.199 theorize allowed the turtles to move from the land into 0:01:18.280 --> 0:01:21.039 the water. This may have saved them in their early 0:01:21.080 --> 0:01:26.080 evolutionary history, specifically during the Permian Triassic extinction, the greatest 0:01:26.080 --> 0:01:29.160 mass extinction ever and one which was spurred by hot, 0:01:29.319 --> 0:01:33.000 dry weather. These insights came after two of the studies 0:01:33.040 --> 0:01:35.959 co authors discovered several specimens of a two hundred and 0:01:36.000 --> 0:01:40.400 sixty million year old turtle named Untosaurus africanus, the oldest 0:01:40.440 --> 0:01:44.240 to known partially shelled proto turtle. These specimens, along with 0:01:44.319 --> 0:01:46.959 another partially shelled turtle found by a young boy in 0:01:47.000 --> 0:01:51.240 South Africa, indicate turtles developed shells for use as digging aids. 0:01:51.960 --> 0:01:55.880 The scientists found similarities between these turtles and gopher tortoises, 0:01:56.080 --> 0:01:58.840 which use their heads and next to brace themselves while 0:01:58.840 --> 0:02:01.680 they dig with their forelimbs. The authors believe that the 0:02:01.760 --> 0:02:04.960 turtle's shell as a protective enclosure is an x adaption, 0:02:05.400 --> 0:02:09.000 meaning an evolutionary trait that originally served one function, but 0:02:09.280 --> 0:02:13.080 winds up serving another. Scientists have been arguing for at 0:02:13.120 --> 0:02:15.960 least two hundred years over whether the turtle's shell evolved 0:02:16.000 --> 0:02:19.600 from bony scales like those on an armadillo or certain lizards, 0:02:19.919 --> 0:02:23.200 or as part of its ribs broadening. Thanks to recent 0:02:23.240 --> 0:02:26.680 discovery of partially shelled stem turtles, it now seems that 0:02:26.720 --> 0:02:34.919 the latter theory is more likely. Today's episode was written 0:02:34.919 --> 0:02:38.000 by Melanie red Zeki McManus and produced by Tyler Clang. 0:02:38.320 --> 0:02:42.040 For more on this and lots of other evolutionarily advantageous topics, 0:02:42.160 --> 0:02:56.000 visit our home planet, how Stuff Works dot com