This book is based on same premise as the successful Aliens love underpants from the same author/illustrator duo, that small children will find the incongruity between everyday pants and imaginary creatures wearing them very funny, and of course they do. But whereas many follow up books are more of the same, this has a very different story which, in my opinion, is the stronger of the two (though no less silly).
Bright amusing illustrations of dinosaurs dressed in flamboyant and colourful pants accompany decent rhyming verse:
"Triceratops was happy, wearing pants on every horn,
Til Styracosaurus snatched them, and they ended up all torn."
Pants are so prized that squabbles erupt and it's dinosaur underwear anarchy as they fight to the death.
[If you are a prehistory stickler, please note that in this story leopard-skin-pant wearing cavemen co-exist with the Jurassic giants which is archaeologically incorrect and the fluffy pink knickers may not accurately reflect the fashions of the dinosaur era.]