Data from: From limb to fin: an Eocene protocetid forelimb from Senegal sheds new light on the early locomotor evolution of cetaceans

Cetaceans constitute a textbook example of the secondary adaptation of
tetrapods to aquatic life. This major event in the evolutionary history of
mammals is often linked in the literature to the limb‐to‐fin transition.
Paradoxically, limb bones are scarce in the fossil record of early
cetaceans, and the transition from a limb‐adapted morphology for an
amphibious life in shallow water to a fin‐adapted morphology for a pelagic
lifestyle remains poorly documented. Here, we describe new protocetid
remains from the upper Lutetian of Senegal, including a nearly complete
articulated forelimb. A cladistic analysis including 24 taxa and 137
morphological characters recovers the new African specimen close to
Carolinacetus. It also confirms that cetacean dispersal to the New World
was not the result of a single colonization event. A 3D model of the
forelimb was reconstructed. Anatomical comparisons suggest that it is
unlikely that the Senegalese forelimb was used as a rigid pectoral flipper
for steering as in basilosaurids and modern cetaceans. Instead, we suggest
that the hand was actively used during swimming. This challenges previous
reconstructions of protocetids as mainly foot‐powered swimmers, and
suggests that swimming specializations of early cetaceans were probably
more diverse than previously considered.