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The pokedex entry shows white pokeball icons that represent all possible evolutions and Pokemon that "form a pair" with it.
Eevee is shown with 8 icons that represent all its different evolutions. If the starters were to have split evolutions, an extra icon would be present, whether as another possible evo or a "pair pokemon", but it's not.
Now, it could be possible that these "split evos" are actually alternate forms of the final evolution. I'm not sure if alternate forms are included in the pokedex entries.
If this is true, I wouldn't expect a totally different looking alternate form. At best, it'll probably have different coloring, a few small changes, and probably different stats. Alternate forms hardly ever stray too far from their original forms (Rotom, Basculin, Sawsbuck, Vivillon). I wouldn't get my hopes up for a drastically different Pokemon. Pretty much all Pokemon that are split by gender are treated as individual Pokemon and not alternate forms (such as Volbeat + Illumise, Gardevoir + Gallade, Wormadam + Mothim).
