The size thing doesn't make sense, since I assume that the height and weight stuff in the PokeDex is for fully grown adults. I mean, a catalogue of animals with humans listed in them would list the average size for humans as 5 or 6 feet - but that doesn't mean they spring out of the womb fully grown. Similarly, I don't think that say . . . a Dratini would hatch from an egg already 13 feet long, but would rather start out small and slowly grow over time.This logic was broken when I realized that some of the pokes that many would accept as not needing a pre-evo were actually quite large. Ekans is over 6 feet by itself. Also, some pokes that were small enough to hatch from an egg were already given pre-evos. (Like Marill) This then becomes a debate on how small is small enough. I realized it makes no difference, although I can't really see a pattern to what Gamefreak does give a pre-evo, other than it's something that they can make into a cute little baby poke. I wouldn't have given a pre-evo to Mantine, but they did.
Oh, and there's no way Dorapion is an evolution of Gligar, since they have no moves, abilities, or types in common with eachother. The only thing related between them is that they're purple, and both loosely based on scorpions - albiet different ways. Evolutions always at least have 1 type in common - Azuril's freakishness excepted. Ground/Flying to Dark/Poison makes no sense.