New research reports that, contrary to popular belief, mammals began their massive diversification 10 to 20 million years before the extinction of the dinosaurs.
Elis Newham, PhD student in Engineering and the Environment and co-author of the study, which is published Proceedings of the Royal Society B, said: “The traditional view is that mammals were suppressed during the ‘age of the dinosaurs’ and underwent a rapid diversification immediately following the extinction of the dinosaurs. However, our findings were that therian mammals, the ancestors of most modern mammals, were already diversifying considerably before the extinction event and the event also had a considerably negative impact on mammal diversity.”
The old hypothesis hinged upon the fact that many of the early mammal fossils that had been found were from small, insect-eating animals — there didn’t seem to be much in the way of diversity. However, over the years, more and more early mammals have been found, including some hoofed animal predecessors the size of dogs. The animals’ teeth were varied too.
The researchers analysed the molars of hundreds of early mammal specimens in museum fossil collections. They found that the mammals that lived during the years leading up to the dinosaurs’ demise had widely varied tooth shapes, meaning that they had widely varied diets. These different diets proved key to an unexpected finding regarding mammal species going extinct along with the dinosaurs. More. Paper. (paywall) – David M. Grossnickle, Elis Newham. Therian mammals experience an ecomorphological radiation during the Late Cretaceous and selective extinction at the K–Pg boundary. Proceedings of the Royal Society B, 2016 DOI: 10.1098/rspb.2016.0256
Note: The thing about mammals (and birds) is that they are space heaters. One wonders whether a cooling planet played a role in their rise in many places.
See also: Researchers: Eardrum evolved independently in mammals and reptiles/birds
See also: Rise of mammals ‘began well before dinosaur extinction’
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