This taxon is considered subjective synonym of
of the valid taxon Elasmosaurinae
according to the Paleobiology Database.
See the page for Elasmosaurinae →
Bibliography
Original description
R. A. Otero. 2016. Taxonomic reassessment of Hydralmosaurus as Styxosaurus: new insights on the elasmosaurid neck evolution throughout the Cretaceous. PeerJ 4:e1777:1-60
DOI ↗