Millenium Man

Orrorin tugenensis, nicknamed "millenium man" by its discoverers Martin Pickford and Brigitte Senut, was found in 2000 in the Lukeino Formation in Baringo, Kenya is the next oldest fossil find that is a possible hominin, at 6 million years old. The finds include femur and humerus fragments, along with some teeth and jaw fragments.

Pickford and Senut believed that Orrorin belongs in the the hominin clade due to its large size (much larger than expected for miocene apes), a suite of postcranial characters that indicate it was a biped, including femurs that are very similar to those of the Homo genus, and its small teeth with thick enamel, which is also similar to the teeth of Homo.

Some of the features that indicate that Orrorin does not belong in the hominin clade include its large, apelike canines. Also, there is not enough evidence to prove that it was bipedal, so more fossils will have to be found to prove that Orrorin is indeed a hominin.

Toumaï: Hope of Life?

The oldest of the proposed hominin is Sahelanthropus tchadensis, a find which consists of a skull, a few mandible fragments and some teeth. Biostratigraphic corelation dates the find to 5.2 to 7 million years old. The find has sparked much controversy, being one of only 2 finds of hominins outside of east Africa, the other being Australopithecus bahrelghazali, both of which were discovered in Chad by a French expidition led by Michel Brunet.

Brunet supports the view that his find belongs in with our earliest bipedal ancestors. He points to the orthognathic (flat) face, large supraorbital torus (brow ridge), canine teeth that are smaller than modern apes, a lack of diastema, a non-functional CP3 honing complex, the horizontal nuchal plane and the anterrior placement of the foramen magnum. For more information, here is the original publication in Nature magazine from 2002: http://www.nature.com/nature/journal/v418/n6894/full/418133a.html

Alternatively, there are some that argue that the TM 266 remains are nothing more than a fossilized ape. Their arguments focus on the small brain size (only 320-380 cc), a U-shaped dental arcade and thin tooth enamel. Some have aruged that female apes can display small canines, and they suggest that this is just a female fossilized ape whose skull was deformed after burial. For more information, here is an article by Milford Wolpoff, Brigitte Senut, Martin Pickford, John Hawks and James Ahern: http://www.paleoanthro.org/journal/content/PA20060036.pdf

What Makes a Hominin?

For the purpose of this blog, it is important that I first establish what exactly merits inclusion into the Hominina subtribe, of which we are the only living members. There are three criteria which need to be met, and those are:

1. The specimen must show differences from chimps and gorillas
2. The specimen must resemble later hominins
3. The specimen must be bipedal

The first two are just based on the principles of evolution, that for a species to be a hominin it must be different enough from its ancestors (which is assumed to be some sort of proto-chimp) that it belongs in a different subtribe than those that went before it. It also must resemble the later hominins in some way because it has to show that those hominins decended from these earlier ones. Lastly, of course, a specimen must be a habitual biped. This is the defining characteristic of hominins, and is what sets us apart from the other primates and mammals.

It is these three characteristics that I will be measuring the early possible hominins against. Over the next few weeks I will be looking at Sahelanthropus tchadensis, Orrorin tugenensis, Kenyanthropus platyops, and Ardipithecus ramidus and kadabba, and presenting evidence for and against their inclusion into the hominina subtribe.