Excerpt from "What makes a mammal a mammal? Our spine, say scientists," posted on NSF News, September 20, 2018.
Mammals are unique in many ways. We're warm-blooded and agile in comparison with our reptilian relatives.
But a new study, funded by the National Science Foundation (NSF) and led by Harvard University researchers Stephanie Pierce and Katrina Jones, suggests we're unique in one more way -- the makeup of our spines. The researchers describe their finding in a paper published this week in the journal Science.
"The spine is basically like a series of beads on a string, with each bead representing a single bone -- a vertebra," said Pierce, curator of vertebrate paleontology at Harvard. "In most four-legged animals, like lizards, the vertebrae all look and function the same.
"But mammal backbones are different. The different sections or regions of the spine -- like the neck, thorax and lower back -- take on very different shapes. They function separately and so can adapt to different ways of life, like running, flying, digging and climbing."
While mammal backbones are specialized, the regions that underlie them were believed to be ancient, dating back to the earliest land animals.
Mammals made the most of the existing anatomical blueprint, or so scientists believed. However, the new study is challenging this idea by looking into the fossil record.
"There are no animals alive today that record the transition from a 'lizard-like' ancestor to a mammal," said Jones, lead author of the study. "To do that, we have to dive into the fossil record and look at the extinct forerunners of mammals, the non-mammalian synapsids."
These ancient ancestors hold the key to understanding the origin of mammal-specific characteristics, including the spine.
But studying fossils isn't easy. "Fossils are scarce and finding extinct animals with all 25-plus vertebrae in place is incredibly rare," Jones said.
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