1.)We see the spine anatomy of a hindlimb supported upright ape in Morotopithecus, Pierolapithecus, Oreopithecus. The data is compelling and extensive - and I have
detailed it in technical raw data form in my book: Axial Character Seriation in Mammals, which republishes my Harvard PhD Thesis. The underlying patterns are extracted and synthesized in my recent PLoS ONE paper “Homeotic Evolution of the Mammals, Diversification of Therian Axial Seriation and a Morphogenetic Basis for Human Origins” and in my Neurosurgical Focus article. The context in evolutionary theory is explained in my recent book “The Upright Ape: A New Origin of the Species” which has a foreword by David Pilbeam - currently Dean of Harvard College and certainly one the most knowledgeable and experienced paleoanthropologists in the world.
2.)We have evidence of an upright hindlimb supported Orrorin based on the femur and Sahelanthropus based on the skull.
3.)There is no convincing fossil evidence at all of a non-bipdeal hominoid outside of the proconsulid group.
4.)We have an early outgroup whose infants have innate bipedal walking(see the video Hominiform Progression).The Siamang video is interesting because of the innate bipedalism. As I point out in the video, John Fleagle has seen young siamangs of this age walk bipedally high in the canopy in Malaysia.
Anyways check out his site if you're interested in reading more.