Hannah Bonner (National Geographic 2012)(ages 8+). In this follow-up to WHEN BUGS WERE BIG, PLANTS WERE STRANGE, AND TETRAPODS STALKED THE EARTH and WHEN FISH GOT FEET, SHARKS GOT TEETH, AND BUGS BEGAN TO SWARM, Bonner explores (in 48-page picture book format) the Triassic, the period when dinosaurs, mammals, and pterosaurs all first appeared.
Bonner's illustrations are lively and fun, while providing a detailed look at the flora and fauna of the era. The text, too, is engaging, full of wit, and surprisingly comprehensive. Altogether, a terrific introduction to the dawn of the dinosaurs.
Here's a Cynsations interview with Bonner from 2008.