1 September 2017
Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world
By Michael Marshall
Species: Struthio camelus
Habitat: most of Africa, especially the reasonably flat bits
Some people just achieve too much. For instance, Iron Maiden singer Bruce Dickinson is also a qualified airline pilot, a skilled fencer and a published novelist – which is frankly galling.
Ostriches are the Bruce Dickinsons of the bird world. Not only are they the largest living bird species, they also lay the largest eggs of any bird alive and hold a Guinness World Record to that effect. And they can run faster.
However, what you may not know is that they are quite possibly the only animal to have two kneecaps in each leg. This we’ve known since at least 1864, but why it should be so has remained a mystery ever since.
To find out, Sophie Regnault and her colleagues at the Royal Veterinary College in London, examined a single dead ostrich donated to the college. They alternately bent and straightened the ostrich’s knees, and used an imaging technique called biplanar fluoroscopy to track how the bones moved. Then they built a simple model to understand how the kneecaps affected the leverage of the muscles controlling the knee.
“The upper kneecap looks similar to the single bone in ourselves and other animals,” says Regnault. However, “the lower one is very closely attached to the lower leg bone… a bit like the point of your elbow.”
Typically, kneecaps improve the leverage of the knee extensor muscles, so they don’t need to produce as much force to straighten the knee. “It’s a bit like putting the door handle further from the hinge,” says Regnault. “It requires less force to open the door.”