One of the best plants I have ever had in my garden was the Maelstorm Snap Dragons. They give sunstones, sandstones, and golden pearls with other things but not fossils.
I know to get fossils other wise I would have to transmute them from stone blocks which I find DS most of the time.
Also I am new to posting on the forums sorry if I violated any rules.
There is a guide on the fan site Wizard101Central that shows all the plant drops :-) I know that fossil is dropped by at least one plant but it drops so many other things its really hard to get the fossil.