Alien city built in a colossal skull on jungle planet

A Giant Alien City on a lush, steamy jungle alien planet. The city is created out of a partially buried giant alien skull that is extremely elongated and has long hollow eye sockets. Part of the skull is removed where communications dishes and antenna protrude. The planet is under attack by the evil cosmic overlord and his shock troops. Done in a dymanic and colorful hard science fiction style