Many historical dates are cited in this book, based upon geologic and paleontological finds. Such estimates are subject to revision, both based upon new evidence and upon finding fault with a prior method of dating or attribution of causality.
For instance, foraminifera, an ancient lineage of ameboid protists, calcify when they die, leaving a rich fossil record. The leaving may be deceiving. The oxygen isotope ratios relied upon for dating climate and life in the oceans are not nearly as reliable as long supposed.
The timing of angiosperms is among the classic questions in evolutionary biology. ~ American botanist William Friedman
Flowering plants were long thought to have evolved 140 million years ago, based upon the fossil record, which is reliant upon finds in wet, lowland areas, where organic decomposition may be inhibited by silt or mud. Yet flowers likely emerged in upland mountainous areas, where fossilization is rare. This is consistent with the understanding that the alternation of wet and dry seasons was probably inspirational for the innovations which characterize angiosperms. Migrating into the tropics was an opportunity for diversity. Evidence found in 2012 pushed the origin of flowering plants back 100 million years or more, to the Triassic.
Whereas the age estimates for non-angiosperm clades are close to their first fossil records, the conflicts between the molecular estimates of clade age and the fossil-first occurrences are greater within angiosperms. ~ Mexican evolutionary biologist Jose Montoya et al
The general trend has been to find evolutionary developments occurring earlier in time than previously thought. With that in mind, treat the dates herein as approximate and go with the flow of the story.