The bees may have been hit by the loss of flowering plants during the catastrophic aftermath of a massive asteroid impact, experts believe.
Their findings, reported in the online journal Public Library of Science ONE, could shed light on the current decline in bee species.
Unlike dinosaurs, bees from the Cretaceous era have left little in the way of fossils. The scientists overcame this obstacle using a technique called molecular phylogenetics, which looks at evolutionary relationships written in DNA.
Dr Sandra Rehan, from the University of New Hampshire, said the findings had important implications for the current decline in bees.