vertebrae from "Zeuglodon hydrarchus", better known as Dr. Albert Koch's "Hydrarchos". , synonymized it with Pontogeneus priscus, which a 2005 study declared a nomen dubium. Reassigned species Basilosaurus drazindai was named by a 1997 study based on a single lumbar vertebra. Originally, the species was thought to have lived in Pakistan and the UK. It was later declared a nomen dubium by Uhen (2013), but Gingerich and Zouhri (in press) reassigned it to the genus Eocetus. This species was at one point in time concluded to be the earliest record of the genus Basilosaurus, before its reclassification. Zeuglodon elliotsmithii, Z. sensitivius, Z. sensitivus, and Z. zitteli were synonymized and grouped under the genus Saghacetus by a 1992 study. Zeuglodon paulsoni from Ukraine (then the Russian Empire) was named by . It was synonymized with Platyosphys but is now considered nomen dubium. Gingerich and Zouhri (in press), however, maintain Platyosphys as valid. Basilosaurus caucasicus also known as Basilosaurus caucasicum or Zeuglodon caucasicum was species described in the Russian Empire, it gets its name from the Caucasus of where it was found in the 1890s. The specimen was found. The fossil was reassigned to the toothed whale Microzeuglodon caucasicum. Basilosaurus harwoodi was discovered in Murray River near Wellington in South Australia, this species classification is quite controversial, yet today it is agreed that the Australian, Basilosaurus harwoodi (or Zeuglodon harwoodi) is most likely a member of the genus Metasqualodon as noted by T. S. Hall 1911. In 1906, German naturalist Othenio Abel thought fossils from the Eocene of Alabama, previously described in 1900 as being a Basilosaurus hip bone by American zoologist Frederic Augustus Lucas, represented the shoulder of a large bird similar to Gastornis, and named it Alabamornis gigantea. Lucas later countered his conclusion in 1908 as he reassigned the fossil specimens to the original conclusion of a Basilosaurus hip bone. Description Basilosaurus is one of the largest animals known to exist between the K–Pg extinction event 66 million years ago (mya) and around 15 million years ago when modern cetaceans began to reach enormous sizes. B. cetoides measured long and weighed more than , while B. isis measured long and weighed nearly . Basilosaurus is distinguished from other genera of basilosaurids by its larger body size and its more elongated posterior thoracic, lumbar, and anterior caudal vertebrae. Basilosaurus does not have the vertically oriented metapophyses seen in its closest relative