On Dec 17th 1992 Gen Suwa discovered the first molar of a new hominid in Aramis, Ethiopia. Some more teeth and bone fragments were found between 1992-94 amounting to 45% of the total skeleton of a specimen nicknamed Ardi, alias of the species defined Ardipithecus ramidus. Curiously, the % of recovered skeleton is similar to what was found from Lucy (Australopithecus afarensis) only 74 km north of Ardi’s place.
Ardi is a female, 120 cm, 50 kg and dated to 4.4 mya. She is the most complete of the early hominids we have found so far, including some key bones: skull, teeth, pelvis, hands, arms, legs and feet. This has increased our knowledge on our earlier ancestors, especially with regards to their locomotion. «Ardi» means «ground floor» and «ramid» means «root» in the Afar language, suggesting that Ardi lived on the ground and was the root of the human family tree.
An area of just 9 km in the Middle Awash valley has produced bones from 35 specimens of Ar. ramidus and more than 6,000 fossils of a vast range of animals. The Middle Awash region is very well known for a few other sites with very important fossils found there, like Bodo (H. rhodesiensis), Herto (H. sapiens of 150 kya), Bouri-Hata (Au. garhi) and Daka (H. erectus).
Also there, an older species of Ardipithecus was found: Ar. kadabba, dated 5.2-5.8 Ma. and proposed to be ancestor of Ar. ramidus. However we have only a few teeth (similar to chimps in size, shape and canine-first premolar occlusion) and postcranial fragments (suggesting bipedal locomotion).
Ardi’s ileum shows clear bipedal characteristics, but the ischium, the pubis and the grasping big toe show that she was still a good tree climber and not a good runner. This is important as breaks some old theories about the bidepal locomotion, which used to consider that bidepalism was developed in the open spaces of the savanna. On the contrary, as Ardi could not run well she needed to stay inside the forest to find protection. Bipedalism was developed by early hominids inside the forests around 5 mya. Then when the savanna started to dominate the landscape c. 1 my later, the bidepalism became the predominant way of locomotion and the climbing features disappeared from the morphology of the hominids.
Most of Ardi’s bones were very fragmented and fragile. The cranium was discovered in 64 pieces. Its reconstruction was not physical but digital, by using microtomography techniques with more than 5,000 images. The following presentation highlights some key aspects of the morphology:
Pingback: Whewell’s Gazette: Year 3, Vol. #30 | Whewell's Ghost