Aegicetus gehennae, a new late Eocene protocetid (Cetacea, Archaeoceti) from Wadi Al Hitan, Egypt, and the transition to tail-powered swimming in whales

Aegicetus gehennae, a new protocetid whale species from the UNESCO World Heritage Site Wadi Al-Hitan (Whale Valley) in Egypt, represents a significant step in the evolution of whales towards tail-powered swimming. This late Eocene fossil, dating back to the early-Priabonian age, exhibits distinctive cranial and postcranial features, including ventrally-deflected exoccipitals and an exceptionally broad sternum. The specimen's vertebral column formula (7:15:4:4:9+) and reduced hind limbs suggest a more fully aquatic lifestyle compared to earlier protocetids. Unlike later whales, Aegicetus likely lacked a tail fluke, indicating that the transition to tail-powered swimming involved mid-body-and-tail undulation rather than a fully developed fluke. This discovery sheds light on the morphological changes accompanying the shift from foot-powered to tail-powered locomotion in early whales.

Gingerich, P. D., Antar, M. S. M., & Zalmout, I. S. (2019). Aegicetus gehennae, a new late Eocene protocetid (Cetacea, Archaeoceti) from Wadi Al Hitan, Egypt, and the transition to tail-powered swimming in whales. Plos One, 14(12), e0225391. https://doi.org/10.1371/journal.pone.0225391