''Kimbetopsalis simmonsae'' was an ancient mammal (a

multituberculate Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...

) which was first discovered in 2015. It lived about 65.5 million years ago, at least a million years after the non-avian dinosaurs went extinct.Carolyn Gramling, Sarah Shelley (image)
How mammals took over the world
ScienceNews; June 7, 2022. – Includes live reconstruction.

References

Cimolodonts Paleocene mammals of North America Fossil taxa described in 2016 Prehistoric mammal genera {{paleo-mammal-stub