See text Basilosauridae is a family of extinct cetaceans that lived during the middle to late Eocene.

[6] Basilosaurids ranged in size from 4 to 16 m (13 to 52 ft) and were fairly similar to modern cetaceans in overall body form and function.

[8] Basilosaurid forelimbs have broad and fan-shaped scapulae attached to a humerus, radius, and ulna which are flattened into a plane to which the elbow joint was restricted, effectively making pronation and supination impossible.

Unlike modern whales, basilosaurids possessed small hindlimbs with well defined femur, lower leg and feet.

[14] The largest known basilosaurid, Perucetus colossus, is believed to be even bigger, with a length of about 17–20 metres (56–66 ft) and possibly comparable to, if not larger than, the modern blue whale in terms of weight,[15] though other researchers argue that it was much lighter.