A sound that hasn’t been heard for at least 66 million years – the supersonic crack of the tail tip of a giant sauropod dinosaur, is now recreated in the lab.

“They were the first living things to have at least part of themselves exceed the sound barrier,” says computer scientist and dinosaur enthusiast Nathan Myhrvold, CEO of Intellectual Ventures, who recreated the sound.

But some palaeontologists doubt the dinosaurs could have snapped their tails repeatedly at supersonic speeds without developing scar tissue that would have left the tail too inflexible to snap again. It remains to be seen if Myhrvold’s new quarter-scale model will convince them that living sauropods snapped their tails on a regular basis.


Sauropod dinosaurs were plant eaters best known for their long necks, elephant-like bodies, and massive legs. Some, including the well-known Apatosaurus also had exceptionally long tails tapering to a long, thin whip-like end.

The bones at the base of the tail were short and stubby but became long and cylindrical at the start of the whip portion.

Bones in the shorter tails of other dinosaurs changed size but not shape along their length, so why did Apatosaurus and other diplodocid dinosaurs evolve such a different tail structure?

Show of strength

In 1989, McNeill Alexander of the University of Leeds, UK, suggested that males might have cracked the tips of their long tails to attract females or display their strength.

The idea caught Myhrvold’s attention while he was head of research at Microsoft, and in 1997 he developed a computer model of the long tail of Apatosaurus. He found that moving the thick base of the tail produced a wave that accelerated down the tapering tail, eventually reaching supersonic speed and snapping at the tip, like a bullwhip.

Not everyone agreed with him. Ken Carpenter, now director of the Utah State University Eastern Prehistoric Museum, says he told Myhrvold the computer results were “garbage in, garbage out, until you prove it” with a physical model. Now Myhrvold has built a model which he described to the Society of Vertebrate Paleontology in Dallas on 15 October.

Myhrvold made quarter-size replicas of all 82 vertebrae in the most complete fossil of Apatosaurus. He added neoprene bumpers to simulate the role of intervertebral discs, and added weights to the vertebrae to model the flesh on the tail.

The complete model weighs 20 kilograms and is about 3.5 metres long, while a living dinosaur’s tail would have weighed about 1300 kilograms and had been 14 metre long.

Mounted on a tripod and balanced with counterweights, the model is moved with a handle. Myhrvold says his colleagues “decided I was going to stand in for the ass-end of Apatosaurus“. When he moved a rod back and forth in a rowing motion the tail rippled in a wave that sped up as it moved along with a supersonic crack at the end.

Sacrificial tail crack

Myhrvold notes that about half of all long sauropod tails have vertebrae damaged from overwork part-way down. He thinks those were males who sacrificed their tails trying to attract mates.

“I am amazed that he has now undertaken the formidable task of building a physical model: it must be a wonderful exhibit,” says Alexander.

But Carpenter still doubts that the model reproduces actual dinosaur behaviour.

The dinosaur might have used its tail to communicate, but not by snapping its tip, says Carpenter. “Think of how a house cat communicates with its tail.”

He says cracking the tip of a dinosaur’s tail would fray the living tissue, forming scabs that could inhibit further cracking. He also thinks the model needs to consider skin texture – the nature of the tip is a mystery but elsewhere the tail “was bumpy, lumpy and rather thick,” and not likely to snap.

But Myrhvold says that the surface doesn’t matter until you get to the very tip, a popper, which makes the sound. On a bullwhip, this is a little piece of string that frays over time and is replaced. On a dinosaur, he says, this was very likely dead skin that would grow off the tip and fray, analogous to our hair or fingernails.

Nobody has found the tip of one of these tails, and they probably wouldn’t fossilise well. But he says it would prove his hypothesis if we were to find skin impressions from the end of a tail, and some long set of filaments at the end without bone, like the popper.

Image: Model of dinosaur tail, Credit: Duncan Smith/Intellectual Ventures