New Scientist tries to keep some perspective about our great-great-etc. grandfather, Ursolestes, a prehistoric primate who might seem to us, a squirrel monkey. To dinosaurs, a giant:
New fossil finds from Montana, US, reveal a species so different from others that some scientists now think the first primates evolved when dinosaurs still roamed.
It weighed between 500 and 1500 grams, the size of a large squirrel, but it would have dwarfed other early primates living at the time about 66 million years ago.
“The big surprise is a primate of such large body size that early in primate evolution,” says Craig Scott of the Royal Tyrrell Museum in Alberta, Canada, who describes the find in the journal Palaeontology.
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Its body mass was some 4 to 10 times that of a typical Purgatorius, making Ursolestes a giant among early primates, but not exceptionally large among post-impact mammals.
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So much primate diversity in the first million years of the Palaeocene also casts new light on a big question in mammalian palaeontology: whether major modern groups originated before or after the dinosaurs left the stage.
Most palaeontologists hold that the evolutionary breakthrough came at the start of the Palaeocene. But co-author Richard Fox of the University of Alberta says the early primate diversity means primates must have originated near the end of the Cretaceous, shortly before the impact.