In 1852,
Joseph Leidy had erected
Pontogeneus priscus based on the centrum of a single cervical vertebra in the collections of the
Academy of Natural Sciences in
Philadelphia. Leidy noted that the centrum had been collected from exposures along the Washita River in
Louisiana. synonymized these two taxa to form
Pontogeneus brachyspondylus which he listed as
incertae sedis. designated
Pontogeneus priscus and
Zeuglodon brachyspondylus to be
nomina dubia based on the lack of diagnostic characters that distinguish the type specimens from other basilosaurids. While
Pontogeneus priscus is no longer considered valid, "Z." brachyspondylus appears similar to
Masracetus from
Egypt (which was also referred to
Z. brachyspondylus in the past) and may represent either a species of
Masracetus or a distinct and closely related but as-yet-unnamed genus. ==Formerly assigned to
Pontogeneus==