Rex

In Rex, by Fred Yager (co-author of Untimely Death), 11-year-old Davy Ross's paleontologist parents go missing from a dig on Mount Kilimanjaro, and he finds a mysterious egg among their belongings. When a tiny dinosaur hatches, Davy has to protect him from an unscrupulous professor, return the tyrannosaurus to its jungle home and locate his missing parents.