Secondary adaptation to aquatic life: an integrative morphofunctional analysis in Cetartiodactyla

• Applicants: Dr. Eli Amson; Privatdozent Dr. Oliver Hampe
• Subject Area: Palaeontology ; Geology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 495352270

Lifestyle transitions are major evolutionary events often reflected by extreme morphological modifications. One particularly obvious example is the secondary adaptation of whales to an aquatic lifestyle. Toothed and baleen whales (Cetacea) are included in the Cetartiodactyla clade with even-toed ungulates (“Artiodactyla”). Their early fossil record documents species within the paraphyletic “Archaeoceti” that are crucial to understand this major evolutionary transition from the terrestrial to the aquatic environment. Members of the earliest known family, the Pakicetidae, were mostly terrestrial with some adaptations to water. They lived during the early Eocene (ca. 50 million years ago). And it is mostly during the middle to late Eocene that the quadrupedal whales “Protocetidae” diversified. They represent a key stage of cetacean locomotor evolution, displaying swimming abilities close to modern otters. This project will focus in particular on a new middle Eocene protocetid from Peru, with exceptionally well-preserved postcranial elements, Peregocetus pacificus. Its postcranial gross morphology and microanatomy will be thoroughly described – combining external morphology observation and measurements to computed tomography data – and compared with other extinct and extant mammals to interpret the function of key anatomical traits. Variables of importance for the land-to-water transition will be further studied with phylogenetic comparative methods. This will involve reconstructing the most likely ancestral states for these variables and mapping the evolution of these aquatic adaptations on the phylogeny of cetartiodactyls. We will identify the most likely evolutionary model that led extinct whales to an aquatic lifestyle by means of evolutionary model comparison. Finally, a multivariate dataset will be used in a phylogenetically informed discriminant analysis to reconstruct the locomotion mode of Peregocetus pacificus and other extinct cetaceans.

• DFG Programme: Research Grants
• International Connection: Belgium, France, Italy, Peru
• Cooperation Partners: Giovanni Bianucci, Ph.D.; Olivier Lambert, Ph.D.; Christian de Muizon, Ph.D.; Rodolfo Salas-Gismondi, Ph.D.