In some cases surgical amputation is performed to remove the duplicate carpals, metacarpals and phalanges. The tarsals (ankle bones) were much more robust than the carpals, but also more disarticulated. Early dinosaurs such as "Eoraptor" tend to have four distal carpals. It glides on flat or slightly drooped wings with carpals flexed and outerwings swept back. "Argyrosaurus" is the only titanosaur known to possess carpals. All of the carpals are well-separated. Almost all carpals (except the pisiform) have six surfaces. It has two non-elongated carpals, with one of the elliptical shape. Like many modern waterfowl, the "Willaru" species had spurs and knobs on their carpals.