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This article was published 8/2/2013 (1503 days ago), so information in it may no longer be current.
A 0.2-kilogram, furry-tailed animal that probably ate bugs may have been the earliest ancestor of mammals, a group of more than 5,100 species including humans, according to the largest-ever study of the group's ancestry.
Researchers mapped genetic data with fossil evidence, creating a new family tree with the hypothetical ancestor, according to a study in the journal Science. They focused on placental mammals, such as humans, dogs and cats, that develop a placenta to nourish the young before a live birth. Scientists have debated the time period when these mammals came into existence. Fossil evidence suggested that after the Cretaceous-Paleogene extinction event when the dinosaurs died, mammals quickly evolved to fill now-empty ecological niches. Genetic data suggested mammals may have evolved earlier. The two were combined for the finding published Thursday, which uses a data set more than 10 times larger than any previous study of mammalian anatomical relationships. "There are many more species to add, and I want to continue to look for fossils that will fit on this tree and tell us more about it, either on the dinosaur or mammal side," said Maureen O'Leary, a study author and paleontologist at the Stony Brook University School of Medicine.
-- Bloomberg News