Sorry Edmasterchaos, looks like we got no Fire-type Platypus in the bunch... unless you think the one on the right might be a beaver-tailed bipedal Pokemon then there might be still hope (though I'm going to spoil that too just below). Similarly Syrusfan's insectoid Grass-type looks like it has no feet to stand on sadly.
Now, as for the Pokemon themselves... I have no idea what to think. Let's take a closer look at each:


Now from the "spiky" tail you'll probably think "Oh, usually spikes mean fire and being it's the tail it's probably the Fire-type". However, the way the tail looks it's not the way "fire spikes" are typically drawn. In addition the body has this sleek look that also ends in points. So while at first you can say "it looks like a Charmander", upon closer look my mind goes away from Fire-type and actually goes to Grass-type. Why? Well let's go to our good friend Shiftry I have placed right next the fist mysterious starter. The tail "flame" look EXACTLY like Shifty's "hands". And with that said, now it isn't to hard to see the slender body, especially the one that ends in points like the head, feet, and overall body, look to be made of leaves as well! Therefore, I'm saying this one is the GRASS-TYPE.


Okay, who combined Turtwig and Buneary? But wait, what about that tail? Can't be a Glameow's, too short... I know, how about from a Spoink or Grumpig (or just Grumpig because I can't find a small image of Spoink)! With that now in mind, this new Pokemon does begin to take on a pig-like look. The tail is the pig's curly tail, the ear does sort of resemble giant close together pig ears, and it's not too hard to put a pig nose on that fave bulge. But what type is it? Well, let's think of other Starters and the animals they usually are. For Grass-types we have all being reptiles (frog, brontosaurus, gecko, turtle), for Water-types we have a two reptiles plus a fish and a bird (turtle, crocodile, mudskipper, penguin), and the Fire-types have a two mammals plus a bird and a reptile (salamander, echidna, chicken, monkey). Well being a pig is a mammal and there is only one starter-type which has that species all to itself, I'm going to have to say that this one is the FIRE-TYPE.

Now as I pointed out above, that flat tail is much like a beavers. Though the reason I have no Bibarel image up there is because other then the tail I don't really have anything else to say about it. I was going to say the ears look sort of like a real beaver's but I decided that really doesn't have much leg to stand on being a lot of animals and Pokemon share that sort of ear. Plus I can't quite figure out what that bulge is around its neck, surely it can't be something like Buizel's and Floatzel's floating ring, right? Either way, out of process of elimination and the fact it sort of looks like a beaver to me which has an association to water, this one will be the WATER-TYPE.