Opinions from K. Carpenter 1999
- 'Alzadasaurus is a subjective synonym of Thalassomedon'
- 'Alzadasaurus colombiensis is recombined as Callawayasaurus colombiensis'
- 'Alzadasaurus kansasensis belongs to Alzadasaurus' according to Welles 1952
- 'Alzadasaurus kansasensis is a subjective synonym of Styxosaurus snowii'
- 'Alzadasaurus pembertoni is a subjective synonym of Styxosaurus snowii'
- 'Alzadasaurus riggsi is a subjective synonym of Thalassomedon hanningtoni'
- 'Brancasaurus belongs to Elasmosauridae'
- 'Callawayasaurus belongs to Elasmosauridae'
- 'Cimoliosaurus snowii is recombined as Styxosaurus snowii'
- 'Cimoliosaurus snowii is recombined as Cimoliasaurus snowii' according to Williston 1890
- 'Cryptoclididae belongs to Plesiosauria'
- 'Elasmosauridae belongs to Plesiosauroidea'
- 'Elasmosaurus belongs to Elasmosauridae'
- 'Thalassonomosaurus marshi is a subjective synonym of Styxosaurus snowii'
- 'Elasmosaurus marshii is recombined as Thalassonomosaurus marshi' according to Welles 1943
- 'Elasmosaurus morgani is recombined as Libonectes morgani'
- 'Elasmosaurus platyurus belongs to Elasmosaurus'
- 'Elasmosaurus serpentinus belongs to Elasmosaurus' according to Riggs 1939
- 'Elasmosaurus serpentinus is recombined as Hydralmosaurus serpentinus'
- 'Hydralmosaurus belongs to Elasmosauridae'
- 'Hydrotherosaurus belongs to Elasmosauridae'
- 'Libonectes belongs to Elasmosauridae'
- 'Microcleidus belongs to Elasmosauridae'
- 'Morenosaurus stocki belongs to Morenosaurus'
- 'Muraenosaurus belongs to Plesiosauroidea'
- 'Plesiopleurodon belongs to Pliosauridae'
- 'Plesiosauridae belongs to Plesiosauroidea'
- 'Plesiosauroidea belongs to Plesiosauria'
- 'Polycotylus ischiadicus is recombined as Thalassiosaurus ischiadicus' according to Welles 1943
- 'Thalassiosaurus ischiadicus is a subjective synonym of Styxosaurus snowii'
- 'Styxosaurus belongs to Elasmosauridae'
- 'Styxosaurus browni is a subjective synonym of Hydralmosaurus serpentinus'
- 'Styxosaurus browni belongs to Styxosaurus' according to Welles 1952
- 'Thalassiosaurus is a subjective synonym of Styxosaurus'
- 'Thalassomedon belongs to Elasmosauridae'
- 'Thalassomedon hanningtoni belongs to Thalassomedon'
- 'Thalassonomosaurus is a subjective synonym of Styxosaurus'
- 'Tuarangisaurus belongs to Elasmosauridae'
- 'Tuarangisaurus keyesi belongs to Tuarangisaurus'