Star Fox Adventures was the last Rare developed game on a Nintendo system before the company was bought by Microsoft, and it was famously not what had initially been planned. It was going to be a new IP called Dinosaur Planet, with creatures called Sabre and Krystal, sidekicks Tricky and Kyte, as well as a wizard called Randorn, starring. It's said that Shigeru Miyamoto saw the work in progress and realised the potential for the title to be part of the Star Fox universe — it's full of talking animals, after all — and the re-design was set in motion.
Some changes were significant, but there was undoubtedly a fair bit of straight-up character model swapping, and this explains why Star Fox Adventures: Dinosaur Planet, as it was almost called, was so different from other entries in the series. Of course, with so much work completed on the original concept there is completed code out there, 60 minutes of which has made it onto YouTube, of course.
You can see the footage below, which includes the original first chapter for Krystal, about 18 minutes, and then assorted clips for the remainder. For those that have run around these environments as Fox, this may be a rather peculiar video to watch.