The 'Underground Astronauts' in search of new human species

Updated 1401 GMT (2201 HKT) May 4, 2016

(CNN)Hidden deep within the innards of a South African cave lay human evolution's equivalent of Tutankhamun's tomb. A treasure trove of 15 skeletons -- eight children, five adults and two adolescents -- all members of a previously unknown species of human ancestor.

In the field of paleontology, uncovering just one complete skeleton has been likened to winning the lottery, but lying here were over 1,500 fossils amounting to multiple jackpots.
This was the largest collection of hominin remains -- part of the human lineage -- ever discovered on the continent.
In 2013, American paleoanthropologist Lee Berger was tantalizingly close to finding them.
But there was a catch.