@nacredambition,
all three major families diversified all over the major southern continents (S Am ,Africa, Asia) ,Therefore diversification of bamboos probably preceeded the evolution of animals like pandas). Forest, Temperate, and savanna clades include abut 250 different species and about 75 genera. The only things they all share are silica based skeletal cells.
Bamboo fossils appear about the the Eocene so original development began while Pangea was still knit together.