Pathfinder Adventure Path: Siege of the Dinosaurs (Extinction Curse 4 of 6) - Rules of Play says:

“Siege of the Dinosaurs” is a Pathfinder adventure for four 13th-level characters. This adventure continues the Extinction Curse Adventure Path, a six-part, monthly campaign in which the heroes lead a traveling circus as they unravel a plot to eradicate all life from the islands of the Inner Sea. This volume also includes a gazetteer of the town of Willowside and lore about the inhabitants of the Abyssal realm of Gluttondark, as well as new monsters and xulgath-themed rules.