For instance, a particularly unique painting of a monkey in a tree may have been illustrated by an Aboriginal who traveled to Sulawesi and brought home tales of exotic creatures, Tacon said.
The galleries also show images of missionaries and human figures with hands on their hips—a gesture associated with Europeans.
Some tableaus also appear to be portraits of faces with distinct European features, Tacon said, indicating that indigenous tribes had close contact with Europeans.
"The Aboriginal culture across the top end of the Northern Territory was much more versatile and used to interacting with other people than previously thought," Tacon said.
However, Sally May, a rock-art expert also from Griffith University, said such relationships may not have been amicable.
For example, many of the sites are "full of images of violence, boxing scenes, spears. It makes you wonder what went on," she said from a base camp near the rock-art site.
In Aboriginal culture, history is an oral tradition, passed on through storytelling. Rock art serves as the only written record of past events.
Throughout the millennia, tribal members have updated the art with different styles and new subjects.
Some galleries have 17 layers of paintings, Tacon of Griffith University said.
In modern times, only senior men in the tribe have the privilege of adding paintings to the rock walls, May said.
"The art is such a high standard," she said. "It's not just a practice run; it's done by experienced artists."
Claire Smith, president of the World Archaeological Congress, called the site "amazingly complex."
"It's a really important site because it's got such a wide range of contact motifs," said Smith, who is not involved with the project.
"Aboriginal elders are passing away, and it's a critical time for documenting ethnographic and culture information," she said.
The researchers recently began excavating the site for archaeological evidence.
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