Why do ostriches, the largest living bird species, with the largest eggs of any bird, have two legs but four knees? Specifically, ostriches have four kneecaps, and therefore four knees. Emus and cassowaries have no kneecaps.
Sophie Regnault, and her research colleagues at the Royal Veterinary College in London, examined a dead ostrich donated to the college.
They 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.
Kneecaps help animals to flex the extensor muscles in their knees, so that they don’t need to exert force to straighten their knees.
However, ostriches have an upper kneecap and a lower kneecap on each leg that act differently from the kneecaps of other animals.
Continue reading “RESEARCH: Why do ostriches have two legs but four knees” →