| Named By: | P. D. Gingerich & M. D. Uhen in 1996 |
| Time Period: | Late Eocene |
| Location: | Egypt - Birket Qarun Formation |
| Size: | Roughly estimated to be around 5 meters long |
| Diet: | Carnivore/Piscivore |
| Fossil(s): | Partial remains of the skull, mandible and post cranial skeleton |
| Classification: | | Chordata | Mammalia | Cetacea | Archaeoceti | Basilosauridae | Dorudontinae | |
Ancalecetus (from Greek ankale, "bent arm", and ketos, "whale") is an extinct genus of early whale known from the Late Eocene (Priabonian, 37.2 to 33.9 million years ago) Birket Qarun Formation (29.3degN 30.0degE / 29.3; 30.0, paleocoordinates 24.6degN 26.2degE / 24.6; 26.2) in Wadi Al-Hitan, Egypt. The species is named after anthropologist and primate researcher Elwyn L. Simons who discovered the type specimen in 1985.
The holotype is a partial cranium (the top of the skull was destroyed by erosion), both dentaries, 20 vertebrae and some sternal elements, partial ribs, and most of both forelimbs. Ancalecetus differs from other archaeocetes and modern whales in having narrow scapulae, very limited mobility in the shoulder joint, and fusion of the humerus, ulna, and radius at the elbow joint. In the wrist, the carpal bones are small like in Zygorhiza, but, unlike in this other basilosaurid, the magnum is fused with the trapezoid in Ancalecetus.