Is Being Mammalian in the Blood or in the Bones?

By Ursula Biba

Classically, mammals have been differentiated from their reptilian counterparts based on their warm-bloodedness, but researchers from Harvard may disagree. Stephanie Pierce and Katrina Jones found that mammalian vertebrae differ significantly from reptilian vertebrae in shape and function, indicating that it’s unlikely for mammals to have evolved from reptilian-like creatures. Though the best data lies in scarce fossil records, Pierce and Jones are looking to museum curators for the best-preserved samples. The National Science Foundation’s Division of Earth Science director, Dena Smith, agrees that the early change in mammalian vertebrae allowed mammals to evolve into today’s recognizable species. Despite hypothesizing that mammalian spinal regions remained unchanged through evolution, Pierce and Jones found that mammalian spines gained new regions near the shoulders and front legs about 250 million years ago. These new regions are believed to have influence how mammals walked. Later, an adaptive region also developed in the pelvis and the spine overall was altered by Hox gene changes. These new findings, and the link between developmental biology and genetics, further the understanding of the definition of a mammal.


National Science Foundation. (2018, September 20). What makes a mammal a mammal? Our spine, say scientists: Study of fossil bones leads to new conclusions about spine's importance. ScienceDaily. Retrieved September 26, 2018 from