Why have tuataras and platypuses outlived dinosaurs?

Answer 1

Luck - being in the right place at the right time. The modern platypus is nothing like old enough to have been around with the dinosaurs though - oldeset fossil - around 100,000 years - dinosaurs were here something like 230 million years ago.-

ANSWER 2: The above is not strictly correct. Platypus fossils indicate that earlier platypuses were very similar to modern platypuses, only bigger, while tuataras have, of course, remained virtually unchanged since they walked with dinosaurs. It would seem that climatic conditions enabled these two creatures to continue to exist. Unlike the dinosaurs, they were not affected by changes further down the food chain. Further, their isolation from the rest of the world enabled them to thrive without the constant threat of predators.