This month ccbc-net (the listserv of the Cooperative Children's Book Center) is discussing series books, from the point of view of which ones are popular now, which ones were popular when the list members were young readers, and whether a "stigma" attaches to paperback series books.
When I was a kid, I read THE THREE INVESTIGATORS, DANNY DUNN, and THE HARDY BOYS. Unfortunately, none of them ever encountered dinosaurs...
So here are a couple of books from paperback series in which the heroes do encounter dinosaurs:
Bruce Coville (Aladdin 1990)(ages 8-12). Book 3 of the Camp Haunted Hills series. Strange things happen at Camp Haunted Hills. Of course, some of this is to be expected, since it's a camp run by movie professionals. But the place really is haunted and, this summer in the middle of preparations for a prehistoric-themed movie, a friendly ghost accidentally sends Stuart and friends to the Cretaceous. When they return, they discover that T.rex, a Maiasaura, and a Triceratops have accompanied them. Can they return them to the past before the present is irrevocably altered?
THE DINOSAURS THAT FOLLOWED ME HOME is light fun with just the right amounts of humor and suspense. The 1990 era illustrations add period flavor, although the novel doesn't feel dated.
K.A. Applegate (Scholastic 1998)(ages 10-14). The second book of the ANIMORPHS: MEGAMORPHS companion series. Five teens and their alien friend have the ability to change into any animal of their choosing, provided they come into close enough contact with the creature to "acquire" its DNA. But they're not using their powers for fun and games -- they're out to save the world from a clandestine takeover by the Yeerks, sluglike parasitic creatures who mentally control their unwilling human "hosts."
In IN THE TIME OF THE DINOSAURS, the group is investigating a sunken nuclear submarine when one of its missiles blows, creating a spacetime rift that sends the Animorphs back to the Cretaceous. There, they encounter, among other things, T.rex, Deinonychus, Spinosaurus, Triceratops, and a hadrosaur or two. And they discover that the earth of the Late Cretaceous is occupied by a pair of alien races, both of whom claim it as their own...
IN THE TIME OF THE DINOSAURS offers a fun, Animorphs-flavored take on dinosaur time travel paired it with alien invasions. An afterward by Tobias -- the only one of the Animorphs who seems to know anything at all about dinosaurs (much to his consternation) -- explains certain, err, inconsistencies with the fossil record :-).