This taxon is considered subjective synonym of
of the valid taxon Styxosaurus snowii
according to the Paleobiology Database.
See the page for Styxosaurus snowii →
Bibliography
Original description
S. P. Welles and J. D. Bump. 1949. Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota. Journal of Paleontology 23(5):521-535