Enhanced descriptions from Syndetics:

A plane crash. A mysterious transformation. An adventure unlike any other. Fourteen-year-old Gerry and his parents are returning to their research camp in the African savannah when their plane crash-lands in the jungle. When Gerry wakes, he has a terrifying shock. He is now a baboon. Using his human intellect and powers of reason, he ensures his survival and growing acceptance by a baboon troop. Just when things are getting comfortable, a shock attack by a leopard triggers Gerry's re-entry into his own body. In hospital, doctors tell him he has woken from a coma-but does Gerry have the scars to prove otherwise?