When comparing functions of the different spines, the researchers saw the nonmammalian synapsid spine acted very differently from both mammal and reptile spines. Its dominant characteristic was its stiffness, with limited capacity for lateral bending, unlike the lateral flexibility of reptile backs. That suggested the long-held notion that these creatures moved like today’s reptiles, particularly lizards, is wrong.

Looking at the spines of the living mammals they sampled, they found that they were sort of a jack-of-all-trades type, displaying abilities in each of the functional traits they measured. This means that mammal backs can do much more than just sagittal (forward and backward) bending, and that during their evolutionary history other functions were added to the stiff backs of their forerunners, such as spinal twisting for grooming fur. The results make the simple lateral-to-sagittal paradigm a much more complicated story.

The researchers cited advances in today’s CT scanning technology, computational data, and statistical programs with making the study possible. They are currently working on further confirming their findings and creating full 3D spinal reconstructions for the species they looked at.

The group believes the work shows the power of the fossil record for testing long-held evolutionary ideas.

“If we only look at modern animals, such as living mammals and reptiles, we can come up with evolutionary hypotheses, but they may not be correct,” Pierce said. “Unless we go back into the fossil record and really dig into those extinct animals, we can’t trace what those anatomical changes were, when they happened, or what selective pressures drove their evolution.”

This work was supported by the National Science Foundation and an AAA Postdoctoral Fellowship.