Whale sex revealed: 'Useless' hips bones are crucial to reproduction - and size really matters, study finds
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It has long been thought that the hip bones of whales and dolphins are essentially useless.
But scientists have now discovered that in fact the opposite is true and that they are very important for mating in the species.
Experts also believe that their shape and size even influences how sexually attractive a cetacean is.
No bones about it: Scientists Matthew Dean (pictured left) and Jim Dines (right) have discovered that the pelvic bones of whales and dolphins (which they are holding) are important for mating and are not useless as previously thought
Both whales and dolphins have pelvic bones, which are evolutionary remnants from when their ancestors walked on land more than 40 million years ago.
Common wisdom has long held that those bones are simply vestigial - slowly withering away like tailbones on humans.
'Everyone's always assumed that if you gave whales and dolphins a few more million years of evolution, the pelvic bones would disappear. But it appears that's not the case,' said Matthew Dean, assistant professor at the University of Southern California (USC).
For four years, he and the Natural History Museum of Los Angeles County's Collections Manager, Jim Dines, have painstakingly analysed cetacean pelvic bones.
Having a whale of a time! Experts say the shape and size of a whale's pelvic bone influences how sexually attractive they are to females. They found that the bigger the testes, the bigger the cetacean's pelvic bone
They wrote in the journal Evolution, the muscles that control a cetacean's highly flexible penis, attach directly to its pelvic bones.
The scientist theorised that the pelvic bones could affect the level of control over the penis that an individual cetacean has, perhaps offering an evolutionary advantage.
To test their idea, they examined hundreds of pelvic bones and used a 3D scanner to make digital models of the curved bones in order to gain an unprecedented level of detail about their shape and size, as well as to compare them.
They then gathered data about testis size relative to the mass of whales. In the natural world, more 'promiscuous' species where females mate with many males, create a more competitive mating environment and the males develop larger testes as a way of attracting females.
Size matters: Males from more promiscuous species such as dolphins evolve larger penises, so larger pelvic bones appear necessary to attach larger muscles for penis control, the experts said. A couple of mating whales are pictured along with others
The experts compared the size of pelvic bones to the size of an animal's testes, relative its body size, and found that the bigger the testes, the bigger the cetacean's pelvic bone.
Males from more promiscuous species also evolve larger penises, so larger pelvic bones appear necessary to attach larger muscles for penis control, they said.
'Our research really changes the way we think about the evolution of whale pelvic bones in particular, but more generally about structures we call vestigial,' Professor Dean said.
'As a parallel, we are now learning that our appendix is actually quite important in several immune processes, not a functionally useless structure,' he added.
The duo believe that their new way of measuring and quantifying the complicated 3D structures of bones, could be used to record and study bones held by museums.
Squealing with delight: Last month, scientists found that dolphins squeal with delight to express their happiness and likened it to a human 'whoop' of triumph
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