venerdì 20 marzo 2015

5 teeth. And 400000 years more

by Siziliano

Two articles in the scientific journals Nature (1) and Science (2) report on findings that set back the origin of the genus ‘Homo’ by 400’000 years. Again in Ethiopia that donated already many traces and fossils for early hominids a novel finding added more information on the origin of ‘Homo habilis’ which is considered the predecessor of modern man. The so far earliest-dated specimen had been found in 1959 and was determined as an age of 2.4 million years.
Now, recently (see cited references), again a mandible has been found that-due to location and stratification where it was found is now dated 2.8 million years of age! The description in the cited literature is educative enough, however, what makes me provide this short note, is the classification: so, how could one date such fossil, and how could ascribe such fossil to a certain species? Chronological date assignment in this region of Ethiopia is based on comparative specimen in the same layer of ground (Fig, 1,2; this part of Ethiopia shows remarkable erosion, bringing easily new findings to the sunlight).

Fig. 1

Fig. 2

The assignment of the found petrified piece of evidence as belonging to the genus ‘Homo’ instead of an older less related antecessor of ‘homo’ comes from its remaining five teeth!!!
Homo habilis’ had (as we modern humans still have) three molars (Fig. 3), in contrast to formerly found elder remains of his/her elder ‘relatives’ that only sported two such molars. Exemplified members with ‘less teeth’ are Australopithecus, i.e., the presence of three molars is species identifying! So, this new hominin (still coined LD 350-1, as no better name has been found yet), is placed in between Australopithecus and Homo habilis.

Fig. 3

The scholars that presented this finding deduced also that this new member already had a larger brain size and a less pronounced jaw, also the fossilized remains of plants identify the habitat as a fairly open steppe with fairly few trees, making bipedal walking a clear advantage.
Article in German (Spiegel-online) at this link.

(1)  Fred Spoor, Philipp Gunz, Simon Neubauer, Stefanie Stelzer, Nadia Scott, Amandus Kwekason & M. Christopher Dean, Reconstructed Homo habilis type OH 7 suggests deep-rooted species diversity in early Homo, Nature 519, 83–86 (05 March 2015) doi:10.1038/nature14224
(2) Brian Villmoare, William H. Kimbel, Chalachew Seyoum, Christopher J. Campisano, Erin DiMaggio, John Rowan, David R. Braun, J. Ramon Arrowsmith, and Kaye E. Reed, Early Homo at 2.8 Ma from Ledi-Geraru, Afar, EthiopiaScience, 2015 DOI:10.1126/science.aaa1343