Unlike many of the Triassic marine reptiles, this particular beast was of Paleogene age, and represented such a novelty in its discovery. Originally framed as a giant crocodilian, its name, meaning “king lizard of Isis,” reflected the view of many mid-1800s giant fossil animals, being of reptilian nature regardless of reptilian characteristics. It wasn’t long after verifiable mammalian elements were identified, and what we know today comprises the longest-bodied archaeocete (“ancient whale,” a paraphyletic grade of pre-crown whales) known.
This follows in a series of reconstructions in which I depict marine tetrapods with elongated bodies, many of which had flipper-like limb modifications, small heads (proportionately) being adaptations to aquatic predation or feeding in some manner or other (there being many variationsof similar adaptations despite distinct ancestry).
Jaime A. Headden
The Bite Stuff 
Jim, Basilosaurus isis was named by Andrews 1914, not by Harlan