Palaeobiological assessment of some basilosauridarchaeocetes (mammalia, cetacea) and its affinity with recent odontocetes: new insights from Wadi El-Hitan, Fayoum, Egypt

Basilosauridae are aquatic Archaeoceti whales, included larger Basilosaurus isis and smaller Dorudon atrox in the middle to upper Eocene Gehannam and Birket Qaroun formations (38–36.5 Ma) of Wadi El-Hitan, Fayoum, Egypt. In this study, 123 specimens of Basilosauridae are discovered from Gehannam and Birket Qaroun formations. B. isis and D. atrox are represented by 116 and 7 specimens, respectively. Gehannam Fm is more productive than Birket Qaroun Fm (86 vs 37 specimens). Preservation and taphonomy of specimens recorded from Birket Qaroun are better than those of Gehannam according to their articulation, completeness, abrasion, and weathering. Comparison between D. atrox and recent odontocetes whales’ Orcinus orca reveals several similarities, for example aquatic habitat, Basilosauridae predatory behaviour, and skull bones arrangement in a usual mammalian pattern. However, D. atrox lacks the cranial telescoping of skull and echolocation capability of O. orca. D. atrox has a fluke like O. orca, but lacks a caudal peduncle like this seen in O. orca. O. orca lacks the hindlimb that occurs in D. atrox. D. atrox was smaller than O. orca; both of them inhabit shallow water and feed on fish and squid but with different mechanisms.