Sunday, April 11, 2010

Lucy, Ardi, and Ida

In lieu of my recent evolution exam, I decided to research the evolution of homo sapiens, also known as anthropogenesis. Humans fall under the genus “homo,” and all 12 species other than homo sapiens have gone extinct. The tribe hominine share several derived characteristics, such as bipedalism, the skull placed directly on top the vertebral column, reduced canines, a more bowl-shaped pelvis, and a loss of toe opposability. Brain size scaled to body size is measured by EQ, or an encephalization quotient. Homo sapiens have an average EQ of 5.8, while basal hominins range from 2.2 to 2.9. The earliest species of the homo was the homo habilis which lived until 1.4 million years ago. It diverged from the Australopithicines. H. habilis has smaller molars and larger brains than the Australopithicines. The homo neanderthalensis, or Neanderthals, died out 24,000 years ago, and a new discovery suggests Homo floresiensis lived up to 12,000 years ago. This ancestor, nicknamed Hobbit, had a remarkably small brain and stature. A skull and tibia of a 30 year old female proposed that she was 3 ½ feet tall.

I found an interesting video on sciencemag.org entitled “The Analysis of Ardipithecus ramidus--One of the Earliest Known Hominids.” On October 1, 2009 paleontologists announced the discovery of a relatively complete skeleton of a small-brained Ardipethecus ramidus female, named “Ardi” which was first unearthed in 1994. Until the discovery of this hominid, the most famous fossil of early human relatives is Lucy, an Australopithecus afarensis. This is an extinct hominid that is common to both Australopithecus and the Homo genus. Lucy lived approximately 3.2 million years ago. She was discovered in 1974. She was 3 feet, 8 inches tall and weighed 65 pounds. Though she looked like a common chimpanzee, she walked upright. Ardi lived one million years before Lucy, and is closer to the last common ancestor between humans and chimpanzee. This ancestor was bipedal, around four feet tall and weighed 110 pounds. She had large arms and hands, and grasping ability of toes. This suggests she was able to climb trees, and probably omnivorous. Most importantly, the skeleton had flexible hands and wrists, so it was not a “knuckle walker” like chimpanzees and gorillas. This shows that chimps and gorillas evolved separately, and our ancestors did not necessarily walk on knuckles like we originally thought.

Another very old famous fossil named Ida was discovered in 1983 in Germany. Its scientific name is Darwinius masillae. It lived approximately 47 million years ago in the Eocene epoch. The single fossil of this genus was a juvenile female that was 23 inches in length and appeared similar to a modern lemur. Though this species is much less associated with human evolution, it is an important intermediate in primate evolution between the strepsirhines and the haplorhines, two subgroups of primates. Ida has several primate characteristics, such as grasping hands with opposable thumbs and nails instead of claws. In addition, Ida along with most primates are generally thought to be adapted to arboreal life, or life in trees. The fossil is 95% complete, and is only missing the left rear leg.

Image 1. Lucy (Australopithecus afarensis) fossil


Image 2. Ardi (Ardipithecus ramidus) fossil


Image 3. Ida (Darwinius masillae) fossil


Posted by Minwoo Ji (11)

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