The diversity of mammals - the group that today includes nearly 5,000 species including humans - on Earth exploded straight after the dinosaur extinction event, researchers, including one of Indian-origin, have found.
New analysis of the fossil record shows that placental mammals became more varied in anatomy during the Paleocene epoch - the 10 million years immediately following the event.
"When dinosaurs went extinct, a lot of competitors and predators of mammals disappeared, meaning that a great deal of the pressure limiting what mammals could do ecologically was removed," said Dr Anjali Goswami from the University College London (UCL).
"They clearly took advantage of that opportunity, as we can see by their rapid increases in body size and ecological diversity," said Goswami, senior author of the study published in the Biological Journal of the Linnean Society.
"Mammals evolved a greater variety of forms in the first few million years after the dinosaurs went extinct than in the previous 160 million years of mammal evolution under the rule of dinosaurs," she said.
Researchers studied the early evolution of placental mammals, the group including elephants, sloths, cats, dolphins and humans.
They gained a deeper understanding of how the diversity of the mammals that roamed the Earth before and after the dinosaur extinction changed as a result of that event.
Placental mammal fossils from this period have been previously overlooked as they were hard to place in the mammal tree of life because they lack many features that help to classify the living groups of placental mammals.
Through recent work by the same team at UCL, this issue was resolved by creating a new tree of life for placental mammals, including these early forms, which was described in a study published in the journal Biological Reviews.
"The mass extinction that wiped out the dinosaurs 66 million years ago is traditionally acknowledged as the start of the 'Age of Mammals' because several types of mammal appear for the first time immediately afterwards," said first author of both papers, Dr Thomas Halliday from UCL Earth Sciences and Genetics, Evolution and Environment.
"Many recent studies suggest that little changed in mammal evolution during the Paleocene but these analyses don't include fossils from that time.
"When we look at the mammals that were present, we find a burst of evolution into new forms, followed by specialisation that finally resulted in the groups of mammals we see today," said Halliday.
The team studied the bones and teeth of 904 placental fossils to measure the anatomical differences between species.
This information was used to build an updated tree of life containing 177 species within Eutheria (the group of mammals including all species more closely related to us than to kangaroos) including 94 from the Paleocene - making it the tree with the largest representation from Paleocene mammals to date.
