A good example of a transitional form in the fossil record, this bipedal prosauropod resides near the base of the sauropod phylogenetic tree. It was described by by Yates et al. (2009) from Early Jurassic South Africa.
Yates, A. M., Bonnan, M. F., Neveling, J., Chinsamy, A. and Blackbeard, M. G. 2009. A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. Proceedings of the Royal Society B. 1440 published online 11 November 2009.