MALE sauropod dinosaurs wooed their lovers and intimidated their rivals by
cracking their tails like huge bullwhips. Or so says Microsoft鈥檚 research
supremo, Nathan Myhrvold.
Myhrvold鈥檚 excursions into palaeontology have generated a number of articles
in the popular press. Now, with the publication of his work on dinosaur tails in
the latest issue of Paleobiology(vol 23, p 353), he has won recognition
from professional palaeontologists.
The idea that sauropod tails were cracked like whips in displays of machismo
was first suggested in 1989 by R. McNeill Alexander, an expert in biomechanics
at the University of Leeds. But until Myhrvold ran a series of computer
simulations of the movement of sauropod tails, no one had seriously tested the
idea.
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The crack of a whip is a miniature sonic boom, caused when the wave
travelling down the whip breaks the sound barrier. The wave accelerates because
a whip tapers along its length, allowing the wave鈥檚 transverse energy to be
converted into forward motion.
After his computer simulations showed that a wave generated at the base of a
13-metre sauropod tail could indeed reach the speed of sound, Myhrvold examined
the tails of eight fossil sauropods. He noticed that the tail vertebrae were
longest at about a quarter of the way down from the tail base鈥攁 known site
of stress in a whip. Half of the specimens had fused vertebrae at this point.
This can indicate a stress injury, and Myhrvold believes these fossils were the
males, who would have cracked their whip in sexual or aggressive displays.
鈥淢ales whipped their tails to get a date,鈥� he says.
鈥淚 put the idea forward with my tongue in my cheek, but I鈥檓 delighted that it
is possible,鈥� says McNeill Alexander. But some palaeontologists remain
sceptical, arguing that the violent motion would damage soft tissues. 鈥淲hipping
delicate blood vessels around at the speed of sound doesn鈥檛 sound like a
wholesome thing to do,鈥� says Peter Dodson at the University of Pennsylvania.
David Morgan, a whip maker based in Seattle, who supplied Myhrvold with a
whip to help his studies, agrees that even a small whip鈥檚 tip eventually frays
from stress鈥攁s would dinosaur flesh. 鈥淏ut if you had a cartilaginous end,
or a renewable one like fingernails, it would stand up,鈥� he says.