WEBVTT - BrainStuff Classics: Why Do Turtles Have Shells?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio. Hey

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<v Speaker 1>brain Stuff Lauren Bogebam here with a classic episode from

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<v Speaker 1>our archives. This one deals with one of the weird

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<v Speaker 1>quirks of evolution. Okay, so most of evolution is pretty weird,

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<v Speaker 1>but this is about how turtles developed their shells. You'd

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<v Speaker 1>think it was for protection, but it turns out that

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<v Speaker 1>that was a side benefit of their original purpose. Hey

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<v Speaker 1>brain stuff, Lauren Bogebam here. Many of us have seen

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<v Speaker 1>a turtle tucking itself into its protective shell, pulling in

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<v Speaker 1>not only it's four legs, but its head and tail

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<v Speaker 1>as well. But while its shell shields a turtle's tender innards,

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<v Speaker 1>it wasn't originally designed for that purpose, as an international

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<v Speaker 1>group of scientists has found. Instead, they say the turtle

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<v Speaker 1>shell most likely began as a digging tool. Tyler Lison,

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<v Speaker 1>who is the lead author of the studying question and

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<v Speaker 1>a paleontologist at the Denver Museum of Nature and Science,

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<v Speaker 1>writes that when turtles first began to veloping shells, a

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<v Speaker 1>major evolutionary transition. The process included a broadening of the ribs.

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<v Speaker 1>Broadened ribs made the turtles thoraxic region or chest more rigid.

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<v Speaker 1>But the puzzling thing is that a rigid chest means

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<v Speaker 1>it's harder for the animal to breathe easily or move swiftly,

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<v Speaker 1>hardly changes that appear to enhance protective capabilities, But that's

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<v Speaker 1>because initially, turtle shells made of more than fifty fused

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<v Speaker 1>bones and their broad ribs were developed not for protection,

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<v Speaker 1>but to lend stability to the turtles so it could

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<v Speaker 1>forcefully dig with its forelimbs. The researchers found being able

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<v Speaker 1>to dig into the ground for food and shelter, they

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<v Speaker 1>theorize allowed the turtles to move from the land into

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<v Speaker 1>the water. This may have saved them in their early

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<v Speaker 1>evolutionary history, specifically during the Permian Triassic extinction, the greatest

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<v Speaker 1>mass extinction ever and one which was spurred by hot,

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<v Speaker 1>dry weather. These insights came after two of the studies

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<v Speaker 1>co authors discovered several specimens of a two hundred and

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<v Speaker 1>sixty million year old turtle name you notice, Saurus africanus,

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<v Speaker 1>the oldest known partially shelled proto turtle. These specimens, along

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<v Speaker 1>with another partially shelled turtle found by a young boy

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<v Speaker 1>in South Africa, indicate turtles developed shells for use as

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<v Speaker 1>digging aids. The scientists found similarities between these turtles and

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<v Speaker 1>gopher tortoises, which use their heads and next to brace

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<v Speaker 1>themselves while they dig with their fore limbs. The authors

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<v Speaker 1>believe that the turtle's shell as a protective enclosure is

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<v Speaker 1>an ex adaption, meaning an evolutionary trait that originally served

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<v Speaker 1>one function but winds up serving another. Scientists have been

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<v Speaker 1>arguing for at least two hundred years over whether the

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<v Speaker 1>turtle's shell evolved from bony scales like those on an

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<v Speaker 1>armadillo or certain lizards, or as part of its ribs broadening.

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<v Speaker 1>Thanks to recent discovery of partially shelled stem turtles, it

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<v Speaker 1>now seems that the latter theory is more likely. Today's

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<v Speaker 1>episode is based on the article the You'll reason turtles

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<v Speaker 1>have shells and It's not for protection on how staff

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<v Speaker 1>works dot com, written by Melanie red Seki McManus. Brain

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