
This comic is based on SECRETS OF LIFE, a 1956 feature-length film in WALT DISNEY'S TRUE-LIFE ADVENTURES Academy Award-winning series of nature documentaries. This 33-page adaptation of the feature-length documentary opens with a splash-page depicting an Allosaurus. Then we're shown the origins of life on primitive Earth, with prehistoric invertebrates such as trilobites, scorpions and giant cockroaches.
As land-life flourishes, we're treated to shots of dinosaurs, including an improbable battle (below) between a Tyrannosaurus rex and a sea-going Pleisosaurus. Finally, we see the development of birds (this comic was produced decades before theories about feathered dinosaurs) and mammals, such as the saber-toothed Smilodon.

A back-cover summary of the contents of WALT DISNEY'S SECRETS OF LIFE, which reads:

All the above is from the Oddball Comics site of Scott Shaw!