During this mass extinction, which happened at the end of the Cretaceous period, 65 million years ago, about 70% of all species of living things became extinct, including ALL surviving dinosaur species.
(this mass extinction; happened; T:at the end of the Cretaceous period) (about 70% of all species of living things; became; extinct; T:During this mass extinction; T:65 million years ago)
this mass extinction about 70% of all species of living things
happened became
T:at the end of the Cretaceous period
extinct T:During this mass extinction T:65 million years ago