The dinosaur extinction was the true starting gun for our evolution
In short: We often imagine mammals diversifying in the shadows of dinosaurs, but new research suggests a different timeline. By synthesizing the world's largest dataset of genetic and physical traits, scientists have reconstructed the common ancestor of all placental mammals—a tiny creature that only began its massive expansion after the great extinction.
For years, the timing of mammalian diversification was a subject of debate. However, a landmark study published in Science reveals that placental mammals—a group including everything from whales and bats to humans—diversified into their present-day lineages much later than previously assumed. The data indicates this major radiation occurred after the K-Pg mass extinction event 65 million years ago, which eliminated non-avian dinosaurs.
To reach this conclusion, an international team utilized 'phylogenomics,' a method that integrates whole-genome sequence data, rare genomic markers, and transposable element patterns. By combining these with 'phenomic' data—observational traits like anatomy and behavior from both living and fossil species—researchers created a more robust tree of life. They specifically used Bayesian molecular-clock frameworks calibrated by the fossil record to narrow down the origins of crown Placentalia to the Late Cretaceous.
The reconstructed common ancestor was not a giant, but a small, insect-eating animal weighing less than a pound with a furry tail. This finding shifts our perspective on how major environmental shocks, like climate change and mass extinctions, set the framework for ordinal diversification. By understanding these deep splits—such as those between Afrotheria, Xenarthra, and Boreoeutheria—scientists can better model how mammals survived past catastrophes and might respond to future environmental pressures.
This research was made possible through collaborative efforts involving the American Museum of Natural History, Stony Brook University, and others. A key tool in this reconstruction was MorphoBank, a cloud-based database that allowed researchers to visualize the physical traits of these ancient ancestors, effectively piecing together an evolutionary 'crime scene' that cannot be repeated.
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Sources
- Summary by Intellect · source: Researchers Reconstruct the Common Ancestor of Placental Mammals
- Also: Phylogenomic Analysis of Placental Mammal Evolution | Phylogeny and Comparative Analysis | Evolutionary Biology | Biological sciences | Topics | Nature Index
- Also: Most comprehensive tree of life to date now includes humans
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