Each picture displays a hypothetical adaptation that an extinct animal could have possessed, such as a plesiosaur disguised on the seafloor like a wobbegong or something that dinosaurs aren't usually shown doing, such as a sleeping Tyrannosaurus.

The second and last major section of the book is titled "All Todays", and depicts animals from the present day as if non-human paleontologists from the future were reconstructing them from fossilized skeletons.

[1] The book and its associated concepts have sometimes appeared in publications covering the nature, history, and 'best practices' of palaeoart, particularly in the context of emphasizing the need for modern depictions of dinosaurs to be consistent with how living animals look and behave.

"[1] All Yesterdays has received mostly very enthusiastic reviews from palaeontologists, and is perceived as introducing or popularising a new "third wave" approach to palaeoart after the classical period of Knight, Zallinger, Burian and others, and the more modern work of Bakker, Paul, Henderson and others.

[5] Writing for The Guardian, palaeontologist David Hone notes that "... the key point is that they are in many ways no more extreme or unlikely than what we see in living species of birds, mammals and reptiles, and no less plausible than many more 'traditional' views of dinosaurs.