Mammals evolved far more quickly in the 10 million years following the mass extinction of the dinosaurs than they did during the previous 80 million years, according to a new study published online Wednesday in the journal Proceedings of the Royal Society B.
In fact, lead author Dr. Thomas Halliday of the University College London Genetics, Evolution & Environment department and his colleagues reported that the evolution of placental mammals (a group that includes nearly 5,000 modern species, including humans) occurred at a near steady rate before the extinction of the dinosaurs 66 million years ago, but exploded soon thereafter.
“Our ancestors – the early placental mammals – benefitted from the extinction of non-avian dinosaurs and competing mammal groups. Once the pressure was off, placental mammals suddenly evolved rapidly into new forms,” Dr. Halliday said in a statement.
“In particular, we found a group called Laurasiatheria quickly increased their body size and ecological diversity, setting them on a path that would result in a modern group containing mammals as diverse as bats, cats, rhinos, whales, cows, pangolins, shrews, and hedgehogs,” he added. In short, the study authors found that the mass extinction event that wiped out dinosaurs had “a marked impact on placental mammal diversification.”
Early mammals benefitted from the decreased competition after the meteor struck.
Placental mammals rising from the ashes of destruction
Dr. Halliday’s team studied the last common ancestor for all placental mammals, a creature which lived during the late Cretaceous period, approximately three million years before non-avian dinosaurs died off following the Cretaceous–Palaeogene (K-Pg) mass extinction. This makes that ancestor 20 million years younger than previously believed, they noted.
By analyzing fossils dating from the Cretaceous to modern day, the researchers were able to estimate the timing of different divergences in the fossil record, thanks partially to an updated tree of life the same team created and released last year. They measured slight changes to the bones and teeth of 904 placental mammal fossils and used the evolutionary tree to map changes to different species anatomy over time.
Based on this data, they were able to determine that the average rate of evolution for these early mammals both prior to the K-Pg mass extinction and afterwards, to determine what impact that event had on the diversification of placental species. Their findings “refute those of other studies which overlooked the fossils of placental mammals present around the last mass extinction,” said senior author Professor Anjali Goswami, a geneticist and earth scientist at UCL.
“Using rigorous methods, we’ve successfully tracked the evolution of early placental mammals and reconstructed how it changed over time,” Professor Goswami added. “While the rate differed between species, we see a clear and massive spike in the rates of evolution straight after the dinosaurs become extinct, suggesting our ancestors greatly benefitted from the demise of the dinosaurs.”
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Image credit: Unsplash
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