Of all vertebrate animals, turtles have one of the stranger body plans. Unlike all other four-limbed critters, which have their shoulder blades riding on the outside of their ribs, the turtle’s ribs are outside of its shoulder blades. This allows turtles to make their shell out of fused bones–the only animal to do so [ScienceNOW Daily News]. Now, scientists have determined that embryonic turtles develop this set-up through a neat bit of origami.
Researchers compared the developing embryos of turtles, chickens, and mice to watch for the point at which turtle development diverged. At first a turtle embryo grows much like a chicken or mouse. But then the developing body wall makes a critical fold, and the usual body plan starts to become an unusual turtle…. The developing muscle tissue that would lie along adult ribs in a standard amniote began to fold underneath itself in the turtle. This tissue tucked inward, bending up to lie below the developing ribs. On this kinked-under section, the shoulder blades, or scapulas, formed [Science News].
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The surprising find of a freshwater, tropical turtle fossil in Arctic Canada suggests that the first turtles to migrate from Asia to North America may have taken the most direct route, swimming and island hopping straight through the Arctic Ocean. This was possible, researchers say, because the Arctic was warmer and ice-free 90 million years ago, when carbon dioxide levels were extraordinarily high. “The fossil record is giving us more and more information about how ancient animals responded to a warming world,” [says] geophysicist John Tarduno…. “They moved toward the poles” [Wired News].
The freshwater turtle was able to survive in the ocean, Tarduno says, because of a floating freshwater highway that led from Russia to Canada. Numerous rivers from the adjacent continents would have poured fresh water into the ancient Arctic sea…. Fresh water, which is lighter than marine water, may have rested on top of the salty ocean water allowing animals such as the turtle to migrate with relative ease [Telegraph].
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The oceans are getting noisier, and that’s bad news for whales, dolphins, and sea turtles who use sound to communicate and navigate, researchers declared at a United Nations wildlife conference. Rumbling ship engines, seismic surveys by oil and gas companies, and intrusive military sonars are triggering an “acoustic fog and cacophony of sounds” underwater, scaring marine animals and affecting their behavior. “There is now evidence linking loud underwater noises with some major strandings of marine mammals, especially deep diving beaked whales” [Reuters], says Mark Simmonds of the Whale and Dolphin Conservation Society.
Researchers have long worried that high-powered sonar pulses confuse whales and dolphins and may cause the animals to beach themselves. Marine mammals are turning up on the world’s beaches with tissue damage similar to that found in divers suffering from decompression sickness. The condition, known as the bends, causes gas bubbles to form in the bloodstream upon surfacing too quickly. Scientists say the use of military sonar or seismic testing may have scared the animals into diving and surfacing beyond their physical limits, Simmonds said [AP]. He points to two recent strandings as possible results of the noisy waters (although a link has not been proved): the 100 melon-headed whales that were found on a Madagascar beach, and the two dozen dolphins that got stranded in southern England.
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It’s a question that has fascinated scientists for decades: When sea turtles and salmon decides to give up the freedom of the open ocean and head back to their birthplaces to breed, how do they find their way back? Some species of sea turtle migrate thousands of miles across entire oceans back to their birthplaces after leaving more than 10 years earlier. And after hatching in rivers, salmon travel hundreds of miles out to sea before returning home to spawn years later [Press Association]. Now one researcher thinks he has the answer. Marine biologist Kenneth Lohmann believes that these marine animals can detect the distinctive magnetic fields of different spots and use them to navigate.
“What we’re proposing is the sea turtles and salmon, when they begin life, basically learn or imprint on the magnetic field that marks their home area,” he said. “They retain this information. And years later, when it is time for them to return, they are able to exploit this information in navigating back to their home area” [National Geographic News]. Lohman says this doesn’t contradict the existing theory that when salmon reach coastal waters, chemical scents guide them upriver to the particular stream where they were born; those olfactory cues probably have a limited range, he says, and couldn’t extend thousands of miles into the ocean to guide the salmon all the way home.
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Three prehistoric turtle fossils dating from 220 million years ago have provided new evidence to fuel the debate over how the turtle’s remarkable shell evolved. The fossils, which were found in southwestern China, show turtles with fully developed shells on their bellies, but nothing above on their backs. Says researcher Xiao-chun Wu: “Since the 1800s, there have been many hypotheses about the origin of the turtle shell. Now we have these fossils of the earliest known turtle. They support the theory that the shell would have formed from below as extensions of the backbone and ribs, rather than as bony plates from the skin as others have theorised” [Telegraph].
Researchers write in their paper in Nature [subscription required] that they named the new species Odontochelys semistestacea, which means toothed, half-shelled turtle. Wu and his coauthor Chun Li say the fossils support the theory that the lower shell, called the plastron, evolved first, and that the upper shell, called the carapace, formed later. This process corresponds with the shell formation seen in turtle embryos and hatchlings [Telegraph].
The new research contradicts the other main theory regarding the evolution of the turtle shell, which holds that the shell evolved from bony plates on the skin that broadened and fused together to form the turtle’s armor. The entire structure would then fuse to the underlying ribs and backbone. (Modern reptiles, such as crocodiles, have these bony plates, as did some dinosaurs, such as ankylosaurs.) The newly studied Odontochelys specimens, however, showed no signs of bony skin plates [LiveScience].
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