Alessandro Palci , Michael W. Caldwell and Randall L. Nydam (2013) Reevaluation of the anatomy of the Cenomanian (Upper Cretaceous) hind-limbed marine fossil snakes
Pachyrhachis,
Haasiophis, and
Eupodophis.
Journal of Vertebrate Paleontology, 33:6, 1328-1342.