Gigantosaurus robustus was named by Fraas (1908). Its type specimen is SMNS 12144, a set of limb elements (right hindlimb), and it is a 3D body fossil. Its type locality is Tendaguru Quarry B, which is in a Tithonian estuary/bay marl in the Tendaguru Formation of Tanzania. It is the type species of Tornieria.

It was recombined as Tornieria robusta by Sternfeld (1911), Stromer (1932), Kuhn (1939), Steel (1970), Swinton (1970), Jain et al. (1979), Paul (1988), Buffetaut (1989), McIntosh (1990) and Bedell and Trexler (2005); it was recombined as Barosaurus robustus by Haughton (1928); it was recombined as Janenschia robusta by Wild (1991), Salgado and Calvo (1993), Chinsamy (1997), Salgado and Calvo (1997), Bonaparte et al. (2000), Wilson (2002), Upchurch et al. (2004), Salgado and Coria (2005), Apesteguía (2005), McIntosh (2005), Curry Rogers (2005), Mateus (2006), Moser et al. (2006), Remes (2007), Mezga et al. (2007), Santos et al. (2009), D'Emic (2012), Le Loeuff et al. (2012), Mannion et al. (2019) and Apesteguía et al. (2021).