Nature & Environment
The Evolution of the Tortoise Shell: How These Animals Kept On Breathing
Catherine Griffin
First Posted: Nov 07, 2014 11:52 AM EST
Scientists may have learned a bit more about the evolution of tortoises. By carefully studying modern and early tortoise fossils, researches have uncovered the evolutionary processes that helped shape their unique breathing apparatus and tortoise shell.
"Tortoises have a bizarre body plan and one of the more puzzle aspects to this body plan is the fact that tortoises have locked their ribs up into the iconic tortoise shell," said Tyler Lyson, one of the researchers, in a news release. "No other animal does this and the likely reason is that ribs play such an important role in breathing and in most animals including mammals, birds, crocodilians and lizards."
Tortoises actually developed a unique abdominal muscular sling that wraps around their lungs and organs to help them breathe. Now, scientists have learned how this particular mechanism evolved. They examined the anatomy and thin sections, also known as histology; in the end, they found that the modern tortoise breathing apparatus was already in place in the earliest fossil tortoise, which lived in South Africa about 260 million years ago.
The tortoise, which was called Eunotosaurus africanus, shared many features with modern day tortoises, but lacked a shell. The fossil of this animal suggests that early in the evolution of the tortoise body plan a gradual increase in body wall rigidity produced a division of function between the ribs and abdominal respiratory muscles. As the ribs broadened and stiffened the torso, they became less effective for breathing. This, in turn, caused the abdominal muscles to become specialized for breathing which then freed up the ribs to become fully integrated into the tortoise shell.
The findings reveal a bit more about the unique breathing mechanism that tortoises use. This, in turn, tells researchers a bit more about the evolution of this remarkable species.
The findings are published in the journal Nature Communications.
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First Posted: Nov 07, 2014 11:52 AM EST
Scientists may have learned a bit more about the evolution of tortoises. By carefully studying modern and early tortoise fossils, researches have uncovered the evolutionary processes that helped shape their unique breathing apparatus and tortoise shell.
"Tortoises have a bizarre body plan and one of the more puzzle aspects to this body plan is the fact that tortoises have locked their ribs up into the iconic tortoise shell," said Tyler Lyson, one of the researchers, in a news release. "No other animal does this and the likely reason is that ribs play such an important role in breathing and in most animals including mammals, birds, crocodilians and lizards."
Tortoises actually developed a unique abdominal muscular sling that wraps around their lungs and organs to help them breathe. Now, scientists have learned how this particular mechanism evolved. They examined the anatomy and thin sections, also known as histology; in the end, they found that the modern tortoise breathing apparatus was already in place in the earliest fossil tortoise, which lived in South Africa about 260 million years ago.
The tortoise, which was called Eunotosaurus africanus, shared many features with modern day tortoises, but lacked a shell. The fossil of this animal suggests that early in the evolution of the tortoise body plan a gradual increase in body wall rigidity produced a division of function between the ribs and abdominal respiratory muscles. As the ribs broadened and stiffened the torso, they became less effective for breathing. This, in turn, caused the abdominal muscles to become specialized for breathing which then freed up the ribs to become fully integrated into the tortoise shell.
The findings reveal a bit more about the unique breathing mechanism that tortoises use. This, in turn, tells researchers a bit more about the evolution of this remarkable species.
The findings are published in the journal Nature Communications.
See Now: NASA's Juno Spacecraft's Rendezvous With Jupiter's Mammoth Cyclone