Thoracosaurus was named by Leidy (1852). It is not extant. Its type is Gavialis neocesariensis. It is the type genus of Thoracosauridae. It was considered paraphyletic by Brochu (2004).

It was assigned to Gavialidae by Hay (1902); to Thoracosauridae by Cope (1871), Cope (1875), Hay (1930); to Tomistomidae by Swinton (1938); to Crocodylinae by Estes and Berberian (1970); to Crocodylidae by Carroll (1988), Erickson (1998); to Thoracosaurinae by Nopcsa (1928), Carpenter (1983), Bryant (1989), Storrs and Efimov (2000); to Gavialoidea by Brochu and Rincón (2004), Brochu (2004), Delfino et al. (2005), Jouve et al. (2006), Vélez-Juarbe et al. (2007), Martin and Buffetaut (2008), Jouve et al. (2008), Puértolas et al. (2011), Salas-Gismondi et al. (2016); to Gavialidae by Rio and Mannion (2021); and to Eusuchia by Darlim et al. (2022).