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The lower jaws of lizards, birds, fish and even dinosaurs are comprised of multiple bones per side. Yet mammals diverged from all other vertebrates and settled on just one bone, repurposing the extra bones into a more elaborate inner ear, perhaps the better to hear. The single bone per side, fused in primates into one jawbone, makes the jaw more rigid. A UC Berkeley paleontologist asks, Did the stiffer, rigid jaw make mammals more successful?

Challenging the lateral-to-sagittal shift in mammalian locomotion Just because they kind of look like reptiles, does that mean they moved like reptiles? For a long time scientists thought so. Nonmammalian synapsids, the extinct forerunners to mammals, like living reptiles, had limbs splayed out to the side instead of beneath like today’s mammals. So scientists believed that they must have also moved in similar ways, with spines more suited to the side-to-side flexing of a sashaying lizard instead of the up-and-down bending typical of a mammal in motion. It was thought that, over time, and i...

 E-Mail IMAGE: Photograph of a skeleton of the early non-mammalian synapsid (ancient mammal relative) Edaphosaurus on display at the Field Museum of Natural History. view more  Credit: Photograph by Ken Angielczyk The backbone is the Swiss Army Knife of mammal locomotion. It can function in all sorts of ways that allows living mammals to have remarkable diversity in their movements. They can run, swim, climb and fly all due, in part, to the extensive reorganization of their vertebral column, which occurred over roughly 320 million years of evolution. Open any anatomy textbook and yo...

The study challenges the lateral-to-sagittal hypothesis by looking at the vertebrae of modern reptiles, mammals, and the extinct nonmammalian synapsids to determine how their vertebrae changed over time and its effect on how these creatures likely moved.