It turns out that the explosion of flowering plant species that occurred about 100 million years ago wasn't necessarily a good thing for evolving mammals. Although scientists once thought that mammals thrived under these conditions, it turns out that they instead declined as flowering plants appeared in the fossil record.
Previous research indicated that the spread of angiosperms, along with the evolution of pollinating insects, may have spurred an increase in the diversity of mammals. This theory seemed to make sense. After all, the radiation would have likely resulted in more food sources for the mammals.