Smallest arm bone in human fossil record sheds light on the dawn of Homo floresiensis

 A paper out today in Nature Communications reports the discovery of extremely rare early human fossils from the Indonesian island of Flores, including an astonishingly small adult limb bone.

Dated to about 700,000 years old, the new findings shed light on the evolution of Homo floresiensis, the so-called 'Hobbits' of Flores whose remains were uncovered in 2003 at Liang Bua cave in the island's west by a team co-led by Australian-New Zealand archaeologist Professor Mike Morwood (1950-2013).

Archaeological evidence suggests these diminutive, small-brained humans inhabited Liang Bua as recently as 50,000 years ago, a time when our own species (Homo sapiens) was already long established in Australia to the south.There has been much debate about the origin of the mysterious humans from Flores. It was first hypothesised that Homo floresiensis was a dwarfed descendant of early Asian Homo erectus.

Another theory is that the 'Hobbit' is a late-surviving remnant of a more ancient hominin from Africa that pre-dates Homo erectus and was small in stature to begin with, in which case possible candidates include Homo habilis or the famous 'Lucy' (Australopithecus afarensis).

Other than Liang Bua, hominin fossils have only ever been found at a single location on Flores: the open-air site of Mata Menge 75km to the east of the cave. Located in the sparsely populated tropical grasslands of the So'a Basin, this site has previously yielded several hominin fossils (a jaw fragment and six teeth) excavated from a layer of sandstone laid down by a small stream around 700,000 years ago.

Pre-dating the Liang Bua hominins by 650,000 years, the Mata Menge fossil remains have been shown to belong to at least three individuals with even slightly smaller jaws and teeth than Homo floresiensis, implying that small body size evolved early in the history of Flores hominins.

However, as postcranial elements (bones from below the head) had not been found in the fossil record at this site it could not be confirmed that these So'a Basin hominins were at least as small as, if not slightly smaller than, Homo floresiensis.

It was also unclear what species the Mata Menge fossils belonged to, owing to the lack of more diagnostic specimens. However, some teeth were deemed to be intermediate in form between those of early Asian Homo erectus and Homo floresiensis.

The new study published in Nature Communications was led by Professor Yousuke Kaifu of the University of Tokyo, Iwan Kurniawan of the Center for Geological Survey in Indonesia, and Associate Professor Gerrit van den Bergh from the University of Wollongong.

sources-science daily