Rodents may have a rule of thumbnails.
Many rodents have curved claws that help the animals climb or dig. But most also have flat nails on their thumbs, researchers report in the Sept. 4 Science. This feature may help the critters deftly break open nuts and seeds, a skill that set rodents up to take over the world.
Rodents make up nearly half of mammals on Earth, with myriad squirrels, mice, rats and more scurrying around the world. Studies have shown that having big teeth and strong chewing muscles to break open hard foods such as nuts — a food source that few ancient mammals could access, meaning less