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Myth busted: Apatosaurus didn’t produce sonic booms when swinging its tail

    No sonic boom: Scientists have created a computer simulation that shows the tail movement of Apatosaurus. Credit: Simone Conti.

    In 1997, Microsoft’s then-technical director, Nathan Myhrvold, made headlines when his computer simulations suggested that the huge tails of sauropods, particularly Apatosaurus-could crack like a bullwhip and break the sound barrier, creating a sonic boom. Paleontologists considered it an intriguing possibility, although some were skeptical. Now a new team of scientists has tackled the problem and built its own simulated model Apatosaurus tail. They found no evidence of a sonic boom, according to a new paper published in the journal Scientific Reports. In fact, the maximum speed possible in the new simulations was 10 times slower than the speed of sound in standard air.

    While still working at Microsoft in the 1990s, Myhrvold, a longtime dinosaur aficionado, came across a book by zoologist Robert McNeill Alexander in which he speculated about whether the tails of certain sauropods might have been used as a bullwhip to produce loud noise as a defense strategy, a mating call, or any other purpose. The structure is somewhat similar to a bullwhip in that each successive vertebra in the tail is about 6 percent smaller than its predecessor. It was already known in physics circles that the cracking of a whip is the result of a shock wave, or sonic boom, resulting from the speed at which the thin tip breaks through the sound barrier.

    Wanting to put that speculative suggestion to the test, Myhrvold began an email correspondence with paleontologist Philip Currie, now at the University of Alberta in Edmonton, Canada. (Fun fact: Currie was one of the inspirations for the Alan Grant character in Jurassic Park.) The two men analyzed fossils, developed computer models and ran several computer simulations to test the biomechanics of the sauropod’s tail. They also compared those simulations to the mechanics of whips.

    They concluded that a lateral movement of the tail could send a wave of energy that accelerates along the length of the appendage and gains momentum so that the tip of the tail reaches speeds in excess of 750 miles per hour. The speed of sound changes depending on the medium and environmental conditions, such as temperature, but is generally pegged at 740 mph in air at 0 °C (32 °F). Myhrvold and Currie noted in their published paper that only the last two to three inches of the tail would reach those supersonic speeds. They also suggested that the furthest part of the tail could have reached beyond the last vertebra thanks to a piece of skin, tendon or keratin – similar to the tips of whips made from cow or kangaroo skin, which are robust enough to withstand supersonic vibrations. speeds.

    Myhrvold updated his research at a conference in 2002, reporting a maximum potential speed of 2,000 km/h, which would have caused a noise boom of about 200 decibels. Among other evidence, some fossil specimens of sauropods have vertebrae fused in a key transition zone between the rigid base and the flexible part of the tail – just as a bullwhip eventually fails at the junction between the thick handle and the flexible leather part.

    Paleontologist Kenneth Carpenter was one of the most outspoken skeptics of the sonic boom hypothesis. “To be blunt, the computer simulations are another case of garbage in, garbage out,” he told The New York Times in 1995. Carpenter said he would be more receptive to the idea if a scale model could be built. It took almost 20 years, but Myhrvold presented just such a model at the 2015 conference of the Society of Vertebrate Paleontology.