![]() Without these changes 260 million years ago, the form that humans have wouldn’t have evolved,” says Angielczyk. ![]() “This is part of our history, why we’re bipedal. The paper’s authors note that the study is important because it illuminates how mammals, including humans, evolved into the myriad forms we see today. Mammals, as they alternately gallop, swim, fly, and stroll, break the rules. Lizards all crawl in the same general fashion, and birds, from penguins to falcons, move their wings more or less the same way. “Cheetahs have flexible spines that let them conserve energy and take bigger strides, humans have unusual vertebral columns that let us walk upright, and whales have stiffer backbones with a few sections that are highly mobile so that they’re better swimmers.”Ĭompared to our fellow four-limbed animals, mammals’ different ways of moving are unusual. “We use our backbones in very distinctive ways that are closely tied to our different modes of life,” says Angielczyk. “The more sub-sections you have, the weirder-looking the result.” With different regions of the spine evolving separately, mammals were able to branch into wildly different body plans. “It’s a little like that drawing game where you fold up a piece of paper and everyone draws a different part of a person-someone draws the head, someone else draws the shoulders, someone else draws the torso,” says Angielczyk. These complex backbones opened the floodgates for mammal diversification. Both the shoulders and the spine play an important role in locomotion, and these simultaneous evolutionary modifications likely reflect changes in how ancient mammal relatives walked and ran. At about the same time, the animals’ upper backs underwent changes too-a move toward the many-sectioned mammal spines we see today. Mammals’ ancient relatives began to evolve smaller, more flexible shoulders about 270 million years ago. In examining these animals’ spines, the team found a pattern. In the Science study, though, Angielczyk and his colleagues, including lead author Katrina Jones from Harvard University, looked for clues in the backbones of mice, alligators, lizards, amphibians, and fossil mammal relatives that lived between about 300 and 190 million years ago. ![]() If mammal spines are an elegant five-course meal, reptile spines are more like a hotdog-eating contest-more of the same.įor years, it was a mystery why mammals’ spines were so much more complex than reptiles’. Reptiles’ spines appear more uniform because the bones in the different sections are all pretty similar. Mammal spines are made up of differently-shaped backbones (or vertebrae) in different sections of the spine-we have thin, flexible neck bones, thoracic vertebrae in our torsos connected to our ribs, and thick, rib-less lumbar vertebrae down by our hips. “And now that we have a better understanding of how mammals’ backbones evolved, it looks like those changes were closely tied to changes that were happening in the shoulders.” “If you look at animals today, mammals stand out because that they have backbones where you can clearly see different regions the vertebrae in each region look different from those in other regions,” says Ken Angielczyk, a Field Museum paleontologist and co-author of a new study in Science. And scientists have just discovered that those flexible shoulders are the key to how mammals’ complex backbones evolved. You can do that because you, as a mammal, have flexible shoulders. If you’re not in public, shimmy a little. Ancient changes to the backbone paved the way for modern mammal diversity.
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