Muraganda Petroglyphs is only giving tokens the +2/+2 buff. It does not give cards like Swordwise Centaur the buff.
In one game I had a 3/3 Elephant token, 3/2 Swordwise Centaur and a Gaea's Anthem, making the Elephant 4/4 and the Centaur a 4/3.
After I played Muraganda Petroglyphs, the Elephant became a 6/6 and the Centaur remained a 4/3. Both creatures have no abilities, yet only the token got the bonus.