The evidence is a partial skeleton -- including arm, hand, leg and foot fragments -- belonging to Paranthropus boisei, dated to 1.34 million years ago and discovered in Tanzania, they said.
The find represents one of the most recent occurrences of P. boisei before its extinction in East Africa, the researchers reported in the journal PLoS ONE.
"This is the first time we've found bones that suggest that this creature was more ruggedly built -- combining terrestrial bipedal locomotion and some arboreal behaviors -- than we'd previously thought," said anthropologist Charles Musiba of the University of Colorado Denver, part of an international research team. "It seems to have more well-formed forearm muscles that were used for climbing, fine-manipulation and all sorts of behavior."
While P. boisei was known for its massive jaws and cranium, displayed by a skull discovered in northern Tanzania in 1959, the build and skeletal adaptations of the rest of the archaic hominin's body have been unknown until recently.
"We are starting to understand the physiology of these individuals of this particular species and how it actually adapted to the kind of habitat it lived in," Musiba said. "We knew about the kind of food it ate -- it was omnivorous, leaning more toward plant material -- but now we know more: how it walked around and now we know it was a tree climber."
The partial skeleton suggests the creature stood 3.5 feet to 4.5 feet tall and had a robust frame, he said.
"We know that it was very strong," Musiba said. "It's unprecedented to find how strong this individual was. The stronger you are the more adaptive you are."