You have a sculpture, an intricate piece of modern art, covered in bulges and blisters. Your task is to weave a cover for it. The fit must be exact. You have to fill in every dent and wrap around every lump. Here’s the catch: you have to make this faultless shroud from a single piece of string that must automatically weave itself into the right three-dimensional shape.
This is the challenge that Sarel Fleishman, Timothy Whitehead and Damian Ekiert from the University of Washington have just overcome. Their “sculpture” is a protein called haemagglutinin, or HA, which sits on the surface of flu viruses. Their “shroud” is another protein designed to perfectly fit onto the contours of HA and neutralise it. They have found a way of fashioning these designer proteins on a computer – a feat that could make it easier to create the next generation of anti-flu drugs.
Hold your arms out with your palm oriented vertically, as if you were trying to shake someone’s hand. Now without moving your forearm, bend your hand downwards towards the floor. Unless you are freakishly flexible, you will only have managed to a measly acute angle. But if you were a bird, you could bend your wrist so that your hand pointed back towards your body. These incredibly flexible wrists allow birds to fold their wings and they help with flying. And many dinosaurs could do something similar.
Many older depictions of small raptors, including the Jurassic Park films, have them holding their arms in a zombie-like stance – arms out at the front and hands palms-down. More recently, artists have portrayed them with more bird-like postures, with their hands bent back towards the forearm. How far the hand could actually bend has been an open question, so Corwin Sullivan from the Chinese Academy of Sciences decided to answer it by piecing together the evolution of the raptor wrist together with Dave Hone (who blogs at Archosaur Musings), Xing Xu and Fucheng Zhang,
Sullivan examined the hands of several dinosaurs, from large hunters like Allosaurus, to smaller, more bird-like species like Caudipteryx and Deinonychus, to living examples like the turkey. He showed that the asymmetric wrists first appeared in this dynasty of predators. They gradually became increasingly asymmetric and backward-bending, culminating in the flexible versions of early birds. This is particularly a tale of two wrist bones – the radiale, which became increasingly wedge-like, and the semilunate carpal, which developed a rounded, convex dip.
These changes to the raptor wrist were already well underway before the group developed powered flight and possibly even before the evolution of long feathers on the arms. For the moment, it’s not clear what advantage the dinosaurs would have gained from their slightly more flexible wrists.