I believe he is talking about the Darwinists who have yet to find one transitional animal after 150 years of looking.
We have found a LOT of previously unseen species in the last 150 years. No satisfactory evidence that they’re “transitional”, but neither is there evidence they aren’t. I’ve not heard anyone suggest my pet theory that at least some of them are really new species as contrasted with merely undiscovered throughout human history.