Fossils indicate that some larger mammals shared the dinosaurs' world, but palaeontologists believe they all disappeared at the same time as the giant reptiles. Only tiny mammals survived, giving rise to all modern forms.
Nicolas Galtier of the Institute of Evolutionary Sciences in Montpellier, France with colleagues in a genetic analysis found that the common ancestor of mammals thought to be puny like a small mouse and living unobtrusively in the shadow of dinosaurs was in fact the size of a small monkey.
Researchers used common features in the genomes of 36 modern mammals to sketch out the genome of the creature from which they descended, the New Scientist reported.
Reconstructing the detailed genome is impossible, but Galtier managed to recover two of its properties. In modern mammals, these properties are correlated with body size and lifespan.
Galtier's results suggested that the common ancestor of all living mammals weighed about one kg and lived over 25 years.
The study was published in the journal Molecular Biology and Evolution.
