Dos Reis and his team therefore “estimated the number of mutations that accumulated in each mammal lineage, corrected for the flaky clock, and together with ages from known fossils estimated the age of the placental ancestor,” he said.
Based on earlier research, it’s thought that this animal was small, nocturnal and pretty scrappy. It either lived far away from the asteroid impact site that caused the extinction of non-avian dinosaurs, or was somehow saved because of its size, habitat and/or lifestyle.
About 70 percent of all species died out during the mass extinction event 66 million years ago, with even some mammals, birds and plants going extinct then.
“To understand why the big lumbering behemoths went extinct and the gracile birds and mammals did not, we need to further explore the fossil record based on predictions shaped by our molecular analysis which, for instance, suggests the age intervals in which we should find evidence of specific mammal groups,” Donoghue told Discovery News.
Michael Benton, a professor in the School of Earth Sciences at the University of Bristol, said he believes that the DNA/molecular clock approach of estimating an animal group's age, used by dos Reis and colleagues, "applies standard, accepted, conservative approaches that take account of missing data in the fossil record."
The first placental mammal might not have looked very human-like, but studies such as this do have important implications for us.
“The relevance to humans is that the placental ancestor is one of our ancestors," Donoghue said.
"It reveals the pattern of assembly of the (basic body plan) that we have inherited. As such, it allows us, for instance, to identify which animals may be best suited to biomedical research to better understand and mitigate congenital diseases.”