The book is a kind of pictorial introduction to the prehistoric world, but it is what the prehistoric world looked like in 1944. The way people in the past thought about their own past is a source of endless fascination, just as much as the way they imagined the future. I think that somebody could probably write a Guided History of Past Imaginings of Dinosaurs if they wanted to: a chronicle of how dinosaurs have been conceptualised and re-conceptualised with each generation.
The art in the book is just completely delightful - and I don't use that word lightly. The illustrator and author, E. Boyd Smith, doesn't even appear to have a Wikipedia entry, but take a look at these pictures and tell me they don't delight you.
Just look at the face on that Tyrannosaur. He seems full of trepidation almost, as though compelled into violence which he does not really seek. The dinosaurs and other prehistoric beasts in the book are so anthropomorphized they are practically people. Everything about their eyes, faces and gestures is so incredibly expressive - even the dimetrodon in the first picture seems almost sad and desperate as he chases after his prey.
What kind of a world was the Boyd-Smithian prehistoric earth? A world thronging with sentient, thinking, feeling, creatures, almost more human than humans. A world of vivid colours and dream-like hallucinogenic vistas. A world that is almost friendly - yet one in which predation is everywhere and nobody can rest for a moment without having to find a way to defend themselves. It's like a world where everything is dialed to 11: everything in it lives with its heart on its sleeve, by turns euphoric, terrified, aggressive and playful.
This dream-dinosaur world is more fantasy than science, as we now know, but I love the idea of it and the vividness of its vision. I want to make a campaign setting there - or, more specifically, a campaign setting on an old pulp vision of a "wet Venus" covered in jungle and volcanoes and inhabited by these uber-emotional beasts. The fertile, fecund, feminine counterpoint to barren warlike authoritarian masculine Mars, as it was imagined, funnily enough, in the 1930s and 1940s - the era of E. Boyd Smith himself.