The vernal awakening has brought rain to Ann Arbor, and right on here on main campus I spotted the rain-splotched silhouette of an articulated human pelvis (left).
iliac blades, and the shortness of the ischium. These features are associated with repositioning key muscles for walking and running on two feet, and are very unlike what is seen in the four-legged, suspensory climbing apes.
rectus femoris, and are allegedly a developmental novelty seen only in hominids (Lovejoy et al. 2009). These traits have led some to claim that Oreopithecus was a hominid, or at least bipedal. Without getting into that debate, I'll just say that seeing these 'bipedal' features in this late Miocene ape's pelvis weakens the case that their presence in Ardipithecus ramidus indicates a unique connection between Ardi and later, true hominids like australopiths.
UPDATE: Check the comments for notes on the Ardi and Oreo fossils from someone who's actually studied them (I myself have only seen pictures and read about them).
Lovejoy, C., Suwa, G., Spurlock, L., Asfaw, B., & White, T. (2009). The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking Science, 326 (5949), 71-71 DOI: 10.1126/science.1175831
Rook, L. (1999). Oreopithecus was a bipedal ape after all: Evidence from the iliac cancellous architecture Proceedings of the National Academy of Sciences, 96 (15), 8795-8799 DOI: 10.1073/pnas.96.15.8795