An intact burial of cremated remains was found in the tomb chamber, known as a cist, wrapped in an animal pelt containing a delicate bracelet studded with tin beads, a textile fragment with detailed leather fringing and a unique coiled bag, they said.
"Visibly it's not as impressive as Stonehenge, but archaeologically it's just as important," Dartmoor National Park chief archaeologist Jane Marchland told the BBC.
Just eight beads have been found on Dartmoor in the last 100 years, she said.
"It was incredibly exciting to lift the lid and a bead fell out."
In a conservation lab researchers have been studying the pelt and its contents.
"The level of preservation we have got is amazing," conservator Helen Williams said. "We're awaiting DNA results on the pelt so we can identify what animal it might have come from."
"Amazing doesn't really do them justice. It's the most extraordinary assortment of finds with tin beads and wooden ear studs."
The beads are the earliest evidence of tin found in the country's southwest, archaeologists said.