A diminutive new basilosaurid whale reveals the trajectory of the cetacean life histories during the Eocene

Abstract

Soon after whales originated from small terrestrial artiodactyl ancestors, basal stem forms (archaeocetes) came to inhabit more specialized aquatic ecologies and underwent a tremendous adaptive radiation that culminated in the adoption of a fully aquatic lifestyle. This adaptive strategy is first documented by the geographically widespread extinct family Basilosauridae. Here we report a new basilosaurid genus and species, Tutcetus rayanensis, from the middle Eocene of Fayum, Egypt. This new whale is not only the smallest known basilosaurid, but it is also one of the oldest records of this family from Africa. Tutcetus allows us to further test hypotheses regarding basilosaurids’ early success in the aquatic ecosystem, which lasted into the latest Eocene, and their ability to outcompete amphibious stem whales and opportunistically adapt to new niches after they completely severed their ties to the land. Tutcetus also significantly expands the size range of the basilosaurids and reveals new details about their life histories, phylogeny, and paleobiogeography.

Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale Perucetus colossus

“… Gingerich (2016) estimated that a 15 m long B. isis weighed 5,840 kg (also see Marino et al, 2000 ; Marino, McShea & Uhen, 2004 ; Uhen, 2004 ), approximately the weight of today’s killer whales ( Orcinus orca ), although this estimate may have a wide range of imprecision (see Gingerich, 2016 ). At about 9 m in length, Cynthiacetus had a smaller body mass than Perucetus , but it was among the larger basilosaurids, which have a range in body sizes ( Corrie & Fordyce, 2022 ; Antar et al, 2023 ).…”