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