Skip directly to content

Tracing the history of placental mammals

Using the world's largest dataset of both genetic and physical traits, NSF-funded researchers have traced the evolutionary history of placental mammals--an extremely diverse group including animals ranging from rodents to whales to humans. This finding marks an important analytical advance in developing tools to reconcile large combinations of behavioral and molecular species data for reconstructing the history of life on Earth. 

The researchers showed that, contrary to a commonly held theory, placental mammals diversified into their present-day lineages after the extinction event that eliminated non-flying dinosaurs and about 70 percent of all species on Earth. During their analysis, the researchers also reconstructed the last common ancestor of placental mammals, a squirrel-like, insect-eating animal. 

The simultaneous analysis of genomic and phenomic (physical traits) data supplied a more complete picture of the tree of life than previous studies that looked at each dataset separately. For instance, an analysis of hard fossil evidence placed the diversification of placental mammals at or just after non-flying dinosaurs became extinct.  However, an analysis of genomic data suggested several of the modern lineages split from each other well before the end of the dinosaurs, when the supercontinent Gondwana began to fragment. 

Students and researchers can access the dataset through MorphoBank, an online resource used to test and generate new hypotheses about the history of life. The research was part of NSF's Assembling the Tree of Life initiative, a multi-year, collaborative project.

Learn more


  • illustration of a hypothetical placental ancestor, a small insect-eating animal
The hypothetical placental ancestor, a small insect-eating animal.
Carl Buell

Recent Award Highlights

corn roots

Deeper roots mean more robust corn crops

Robust roots improve corn's drought tolerance and fertilizer efficiency

Research Areas: Biology Locations: Pennsylvania
a powerful algorithm helps researchers map complex cell development

Mapping cell development one line at a time

The Wanderlust algorithm allows researchers to study single cells as they transform into tissues and organs

Research Areas: Biology Locations: New York