Fresh evidence from the University of Bristol shows that mammals had already evolved to live outside of trees and on the ground long, long before the asteroid hit that wiped out the dinosaurs. The new study, in the journal Palaeontology, describes how the transformation in the way mammals lived took place millions of years before the mass extinction occurred.
By studying small fossilized bone fragments, especially the limb ends, found in Western North America, the research team found important indicators that marsupial and placental mammals were evolving towards a more terrestrial way of life. The bones, previously under-emphasized in research, have distinct markers that point to the mammals’ locomotion patterns. The researchers used these bone remains to analyze the locomotor habits of whole groups of mammals, and this provided them with valuable insights into their adaptive evolution.
Lead researcher Professor Christine Janis of the University of Bristol’s School of Earth Sciences explained how, as plant life began to develop toward the end of the Cretaceous period—namely with the development of flowering plants—mammals were already becoming accustomed to a life on land due to these changing environments. Although it was understood that mammals that lived in trees were challenged following the asteroid impact, the contribution of habitat change to inducing this behavioral shift had not been investigated fully until the present.
This research is a radical change in the field of paleontological studies. Previous studies employed complete skeletons in examining the history of mammalian movement, yet this study is one of the earliest to employ small bone pieces in examining the locomotory changes in mammals over time. Drawing statistical evidence from museum collections in New York, California, and Calgary, the scientists were able to study those tiny fossils in precise detail.
Professor Janis cited the contribution of vegetational habitat to the evolutionary changes experienced in the Cretaceous period, suggesting that the changes had more influence on mammalian evolution than any influence exerted by dinosaurs. This trailblazing research sheds new light on the lives and habits of prehistoric mammals and how they have adapted to a changing world millions and millions of years ahead of time when the asteroid devastated life on Earth.
