What counts as an ability for the purposes of Muraganda Petroglyphs?

Question

Say I control both Muraganda Petroglyphs and Life and Limb - am I correct in assuming that my Forest Saprolings do not get +2/+2 from the Muraganda Petroglyphs, because they have a mana ability?

For reference, they are forests, and rule 305.6 states the following:

305.6. The basic land types are Plains, Island, Swamp, Mountain, and Forest. If an object uses the words "basic land type," it's referring to one of these subtypes. A land with a basic land type has the intrinsic ability "{T}: Add [mana symbol] to your mana pool," even if the text box doesn't actually contain that text or the object has no text box. For Plains, [mana symbol] is {W}; for Islands, {U}; for Swamps, {B}; for Mountains, {R}; and for Forests, {G}. See rule 107.4a. Also see rule 605, "Mana Abilities."

Answer 1

Gatherer has the following ruling:

Animated basic lands have mana abilities, so they won't get the bonus.

So your assumption is correct: any land that has become a creature does not get the bonus from Muraganda Petroglyphs (except in the rare case where the land has lost its mana ability -- and I'm not aware of any card that actually does this).

Answer 2

Any ability text on the card, or any ability granted to the card through an equipment, aura, or other effect would be an ability for the purposes of Muraganda Petroglyphs. In this case the ability is granted by Life and Limb, giving them the basic land type also gives the basic land type's ability of tap for mana.

As a general rule of thumb, if the creature were to have this naturally, would it appear in their text box. Power and toughness effects don't, the creature just has the power and toughness, though abilities that modify power and toughness under certain conditions (when attacking say) do. Supertype, type and subtype don't they are on the type line. Color is set by the cost usually, though it has been ruled that color setting in the text box is no longer an ability. But keywords granted, such as Lifelink and Deathtouch from Basilisk Collar, activated abilities, and triggered abilities granted by outside sources all do count.