Scientists have discovered the most complete skeleton ever recovered of an ancient relative of humans, concealed in a rock that had been unearthed from an archaeological site three years ago.

South African researchers on Thursday said that the rock, which contained one of the most important archeological finds to date, had sat undisturbed in a laboratory until a technician noticed a tooth sticking out of the back of the three-foot wide stone in June.

"I was lifting the block up, I just realized that there is a tooth," the technician, Justin Mukanka told AFP.

When the rock was scanned, scientists found the remains of a juvenile hominid skeleton of the Australopithecus (southern ape) sediba species, which according to University of Witwatersrand paleontologist Lee Berger is the "most complete early human ancestor skeleton ever discovered," according to a university news release.

“We have discovered parts of a jaw and critical aspects of the body including what appear to be a complete femur (thigh bone), ribs, vertebrae and other important limb elements, some never before seen in such completeness in the human fossil record,” Berger said.

“This discovery will almost certainly make Karabo the most complete early human ancestor skeleton ever discovered. We are obviously quite excited as it appears that we now have some of the most critical and complete remains of the skeleton, albeit encased in solid rock. It’s a big day for us as a team and for our field as a whole,” he added.

Scientists believe that the remains of the skeleton dubbed "Karabo" are around two million years old.  The rock that contained Karabo was first discovered in 2008 in the oldest continuous paleontological dig site in the world, the renowned Cradle of Humankind located just north of Johannesburg.

Researchers still do not know whether the species, which possessed long arms, a small brain and a thumb, which scientists believed was used for precision gripping, was a direct ancestor of humans' genus, Homo, or simply a close relative.

Scientists believe that Karabo would have been between the age of nine and 13 when the upright-walking tree climber met its end.

Four other remains of A. sediba skeletons have been discovered in South Africa's Malapa cave, located about 30 miles north of Johannesburg, since 2008 and they are all believed to fallen into a pit in the cave and died.

The skeletal remains of the sediba pre-humans are considered by some to be the most complete remains of any hominids found and are possibly one of the most significant paleoanthropological discoveries in recent time.

The University of the Witwatersrand also announced that the process of exploring and uncovering fossil remains will be conducted on live video and streamed online in real time.

Researchers said that a special laboratory studio will be built at the Cradle of Humankind within a year, according to Qedani Mahlangu, a regional minister of economic development.

“The public will be able to participate fully in Live Science and future discoveries as they occur in real time – an unprecedented moment in paleoanthropology,” Berger said. “The laboratory studio will be also linked to laboratories at Wits University and the Malapa site.”