Plot hole: Although the errand bird always insists on the postage and even asks for additional fees for more than twenty words, he never gets any payment from the assigning characters.
Plot hole: The dinotopian island is so large that there are mountain ranges, massive rivers, and whole towns so far apart that it takes days to travel between them. Yet this island is also so close to the mainland that they stumble upon it with a single engine propeller driven airplane. Such a land mass would be just a little hard to miss.
