"into Australian Aboriginal rock paintings" is a prepostional phrase. A prepostional phrase is in form of prepostion plus object. In your example "into" is prepostion. "Australian Aboriginal rock paintings" is object of prepostion. An useful link about prepositional phrases: http://www.english-grammar-revolution.com/prepositional-phrases.html

No, "into" is a preposition that introduces a prepositional phrase.