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June 21, 2010

Salassie News ItemDr. Yohannes Haile-Selassie is the Curator and Head of Physical Anthropology at the Cleveland Museum of Natural History is a former Post-Ph.D. Research Grantee who was also awarded a Professional Development Grant (now known as the Wadsworth International Fellowship) to pursue a doctorate in physical anthropology at the University of California, Berkeley, CA, under supervision of Dr.Tim D. White. His recent findings are to be published online this week in the Proceedings of the National Academy of Sciences (PNAS). Below is the press release just released by PNAS announcing his discovery and the implications of the findings for our understanding of Human Evolution.

PRESS RELEASE

HUMAN-LIKE WALKING IS ANCIENT: “Lucy’s” Forebears were Advanced Upright-Walkers.

Addis Ababa, Ethiopia:

An international team of scientists conducting field research in the Woranso-Mille area of the Afar region has announced the discovery of a 3.6 million-year-old partial skeleton of “Lucy’s” species, Australopithecus afarensis (“Lucy” is 3.2 million years old). This discovery and results from the initial analysis will be published this week in the Early Online Edition of the Proceedings of the National Academy of Sciences (PNAS) of the United States of America. The first author and team leader Dr. Yohannes Haile-Selassie, Curator and Head of Physical Anthropology at the Cleveland Museum of Natural History, said “as a result of this discovery, we can now confidently say that “Lucy” and her relatives were as proficient as ourselves walking on two legs. Obligate bipedality has deeper roots.”

The new partial skeleton (KSD-VP-1/1), which the authors have nicknamed “Kadanuumuu” (kah-dah-nuu-muu), generates new information on the locomotion, shoulder girdle morphology, and shape of the rib cage in our early ancestors, particularly in “Lucy’s” species, Australopithecus afarensis. “Kadanuumuu” means “big man” in the Afar language and reflects its large size. One of the co-authors, Kent State University Professor of Anthropology Dr. C. Owen Lovejoy, described the new partial skeleton as “a truly special find in understanding the early evolution of humans. "

Background to the Discovery:

The best-known direct early human ancestor is Australopithecus afarensis. The only partial skeleton assigned to this species, until now, has been “Lucy”, a female individual recovered from Hadar, in Ethiopia’s Afar Triangle in 1974, and dated to 3.2 million years ago. “Lucy” was an exceptionally small female (only about 3 1⁄2 feet tall), but she was the only partial skeleton of her age ever found. Many interpreted her small frame as being incompletely adapted to upright walking.

The new Woranso-Mille specimen (KSD-VP-1/1) being reported here is only the second partial skeleton ever recovered and it is a large male (about 5 to 5 ½ feet tall). It is also now the oldest Australopithecus afarensis skeleton yet found and among the largest individuals of the species. It not only preserves most of the same skeletal parts that “Lucy” does, but also others never previously known, including a nearly complete shoulder blade and a significant portion of the rib cage. These have generated many surprises and shed major light on previously unknown skeletal features of Australopithecus afarensis, thereby advancing our knowledge of the paleobiology of this species and its descendants.

Discovery of KSD-VP-1/1 (“Kadanuumuu”):

The Woranso-Mille project has been conducting field research in the central Afar region of Ethiopia since 2004. The project has collected more than 4500 fossil specimens of various mammalian species. These include about 95 fossil hominid specimens dating back to 3.8 million years ago.

On February 10, 2005, Alemayehu Asfaw found the first element of KSD-VP-1/1, a fragment of the lower arm bone (ulna), at a locality known as Korsi Dora. The specimen was exposed on the surface and further investigation resulted in the recovery of more elements. The surface distribution of the specimens indicated that excavation was necessary. Continued excavation between 2005 and 2008 produced more skeletal elements including an upper arm (humerus), a collarbone (clavicle), bones of the neck (cervical vertebra), a shoulder blade (scapula), ribs, pelvis, sacrum, a thighbone (femur), and a shinbone (tibia). Most of the specimens were buried under 1.5 meter thick clay and silt. All of this was removed before the specimens could be recovered. Unfortunately, none of the cranial or dental parts were recovered. Dr. Haile-Selassie explained that extraction of the skeletal elements from the ground took five years of excavation.

Geography:

The specimen was found in the Woranso-Mille Paleontological Project study area located in the central Afar region of Ethiopia about 210 air miles (336 Kms) northeast of the capital Addis Ababa and 30 air miles (48 Kms) north of Hadar (“Lucy’s” site). Korsi Dora is the local name for the area where KSD-VP-1/1 was found. This area is inhabited by the Afar people who are semi-nomadic.

Geology and Age Determination:

A. Geochronology and stratigraphy

KSD-VP-1/1 was recovered from mudstone at the base of an exposure of upward coarsening claystone, siltstone and sandstone about one meter thick. A volcanic tuff about 2.6 meters below the specimen has been dated by the 40Ar/39Ar (“Argon-Argon”) method, yielding an age of 3.60 ± 0.03 Ma.  

B. Paleomagnetic Analysis

Paleomagnetic analysis was conducted to further refine the specimen’s age, since it was found above the dated tuff.  Extensive samples were taken from material above the specimen. All exhibited what is known as normal “remanence” (the directionality of the Earth’s magnetic poles has shifted back and forth in cycles for much of its history). This tells us that the bottom of the deposits on which the specimen rested is just above the “Gauss/Gilbert paleomagnetic transition,” indicating an age of between 3.6 and 3.3 million years ago. Using sedimentation rates calculated for other parts of the study area, KSD-VP-1/1, which was found 2.6 meters above the dated tuff, has a most probable age of 3.58 million years.

Significance of the Discovery:

  1. “Lucy” was an exceptionally small female (only about 3 ½ feet tall), but she was the only partial skeleton of her age. “Kadanuumuu” is a much larger male (5 to 5 ½ feet tall), and not only preserves most of the same skeletal parts that “Lucy” does, but also some never previously known, including a nearly complete shoulder blade and a significant portion of the rib cage. These have generated many surprises.  
  2. Many anthropologists mistook some features of “Lucy’s” small frame to indicate that she was not fully adapted to upright walking. “Kadanuumuu” shows this was incorrect. His much larger frame exhibits characters very similar to those of modern humans in his pelvis, thigh, and shinbones.
  3. In fact, “Kadanuumuu’s” legs were also surprisingly long—almost as long compared to the size of his arms as are those of modern humans. Elongating our legs was previously thought to be a pivotal change later in human evolution, and most observers thought “Lucy’s” legs were very short. However, her legs were short because of her very small size. “Kadanuumuu’s” legs demonstrate that if “Lucy’s” frame had been as large as his, her legs would also have been almost as long as ours. Speculation as to why our legs got longer over time has ranged from helping dissipate body heat to reducing the energy needed to walk long distances (claimed by some to be an adaptation for “persistence hunting”). However, the latter now cannot be correct because “Kadanuumuu” lived nearly one million years before the first stone tools were ever made (he is 400,000 years older than “Lucy”).
  4. “Kadanuumuu’s” shoulder was also a major discovery. It shows that our ancestor’s shoulder blade and rib cage were much more similar to those of modern humans than has been previously thought. Most authorities, until now, presumed that our ancestors’ shoulders were more like those of chimpanzees. “Kadanuumuu” shows that this is not the case. Along with specimens from an even older ancestor, Ardipithecus ramidus or Ardi (See the October 2, 2009 special issue of Science), this c