Where do elbows and knees come from? Biologists track them back to our boneless, sharklike ancestors

Ask an older person where painful arthritis strikes and most will point to their joints—knees, hips, and fingers. That’s because as people age, those joints lose the cartilage and viscous fluid, known as synovial fluid, that keeps them supple. Sharks and skates have no bones—and no arthritis—but they apparently have the same kind of joints we do. Once thought to exist only in bony vertebrates, these so-called synovial joints actually evolved in the much older ancestor of cartilaginous and bony fish , researchers reported earlier this month in a preprint on bioRxiv. “They very convincingly show that all living jawed vertebrates have synovial joints,” says Gage Crump, a developmental biologist at the University of Southern California who was not involved with the work. “[It] extends the [joints’] evolutionary history.” Because many aquatic creatures can regenerate their injured joints, studying their evolution may lead to better treatments for arthritis and other joint problems in humans, says study author Neil Shubin, an evolutionary biologist at the University of Chicago. Our bodies depend on several kinds of joints. Sutures, as in the skull, don’t move in adults, and cartilaginous joints, such as those that connect the ribs to the sternum, tend to have very limited mobility. But most bone-to-bone connections in humans are synovial joints, where a fluid-filled cavity connects adjoining bones, and cartilage allows for maximum and smoot...
Source: ScienceNOW - Category: Science Source Type: news