Dakosaurus was named by Quenstedt (1856) [Sepkoski's age data: J Oxfo K Haut-l Sepkoski's reference number: 2,620]. Its type is Geosaurus maximus.

It was synonymized subjectively with Steneosaurus by Hulke (1869); it was misspelled as Dacosaurus by Sauvage (1873), Quenstedt (1882), Delair (1958), Charig (1967), Carroll (1988), Sepkoski (2002), Gasparini et al. (2006), Buchy et al. (2007), Young et al. (2010), Nascimento and Zaher (2011), Cau and Fanti (2011), Bronzati et al. (2012), Young et al. (2013), Young (2013), Young et al. (2014), Herrera and Vennari (2014), Sertich and O'Connor (2014) and Parrilla-Bel and Canudo (2015).

It was assigned to Amphicoelia by Owen (1861); to Mosasauria by Sauvage (1873); to Dinosauri by Quenstedt (1882); to Teleosauridae by Delair (1958); to Crocodilia by Sepkoski (2002); to Metriorhynchidae by Carroll (1988), Gasparini et al. (2006) and Buchy et al. (2007); to Thalattosuchia by Charig (1967) and Bronzati et al. (2012); to Geosaurini by Cau and Fanti (2011), Young et al. (2013), Young (2013), Young et al. (2014) and Herrera and Vennari (2014); to Neosuchia by Nascimento and Zaher (2011) and Sertich and O'Connor (2014); and to Geosaurinae by Young et al. (2010) and Parrilla-Bel and Canudo (2015).