Doyle published The Lost World well after both killing off and reviving Sherlock Holmes. He wrote about Professor Challenger and Holmes concurrently for about fourteen years, and continued to write Professor Challenger stories for a few years after the last Holmes story.
Doyle always had a kind of CSI-esque "five seconds in the future" attitude toward science in the Holmes stories, and toward the end of that series more speculative elements were included. These remind me of the center-stage speculative elements of the Professor Challenger stories (though not as spiritualist), which leads me to wonder:
Do the original Doylian texts give any indication that Sherlock Holmes and Professor Challenger occupy the same fictional world?