ECHO - Evolutionary Convergence in Historical Oceans: The case of whales and ichthyosaurs

The research project ECHO aims to understand the phenomenon convergent evolution through a classical example: Whales and ichthyosaurs. Whales are mammals, whereas ichthyosaurs are extinct reptiles, and both groups had ancestors on land. We use data from the inside and the outside of their skeletons to answer how ichthyosaurs evolved the ability to give live birth under water, whether the fish-shaped body is an unavoidable result of swimming fast in the oceans, and whether these two animals were feeding in the same way. In order to understand the evolution of the ability to give live birth under water, physiological processes are key, especially thermoregulation and growth rate. Data for investigating this can be gained from inner microstructure in bones, whether they are fossil or extant. Since the start of the project, we have collected data from some of the earliest ichthyosaurs as well as their descendants that are 100 million years younger, both from the museum collection at the Natural History Museum in Oslo and from collections in Zürich, Paris and Washington DC, and from modern toothed whales for comparison. The data are a combination of thin sections and CT data, and we are now in the process of using qualitative and quantitative methods to analyse the structures that we observe. Through this, we have learnt that it is necessary to expand and refine the statistical methods we use to also include other skeletal elements than femora, and this is a work we started during a methodological workshop we organized in October 2023. As for output, we have presented our preliminary results in three scientific conferences out of which one was an invited key note lecture (Delsett at II Meeting in vertebrate paleophysiology, Sorbonne). One paper is currently in review and a second one about to be submitted. Postdoctoral fellow Mathieu Gabriel Faure-Brac also published a paper in early 2024 on amniote thermoregulation that underpins some of the work we are currently doing, and gave an interview for forskning.no. We also aim to study the evolution of the fish-shaped body of whales and ichthyosaurs and how it relates to locomotion. In order to do this, we are currently establishing a measurement database for ichthyosaur specimens that will be compared to whales in the upcoming year. We have also established a collaboration with the University of Edinburgh and their Engineering department to make biomechanical models for how movements in a vertebral column affect the inner microstructure of the bones. This will be important also when we analyze CT data for fossil whale vertebrae that we are collecting from the Smithsonian’s NMNH. The third part of ECHO is about feeding under water, focusing on how ichthyosaurs and whales use their hyoid apparatus (“tongue bones”). We have published one paper where we studied the shape of these bones through time and between ichthyosaurs and toothed whales. We found that ichthyosaurs had too slender hyoid elements to ever evolve suction feeding, which is surprising knowing how common this feeding mode is in the ocean. The next phase of this research aims to understand the biomechanics of the hyoid, where we will use CT data showing the inner architecture of the bones, which will be analysed together with collaborators at the University of Edinburgh. PI Lene Liebe Delsett has given talks about the project for kindergarden teachers, biology students, high school students, young researchers and for families. She has also presented the work in two podcasts: Naturfagpodden and Livet, universet og alt. Delsett has written two essays for Morgenbladet, about deep sea mining and menopause in toothed whales, and one for Paleobloggen, about fossil whales that were claimed to be larger than the blue whale. Delsett and Faure-Brac are hired full time to work on the project. To technicians are hired for the post processing of CT scan data and for establishing the measurement database. In addition, ECHO cooperates with colleagues at the natural history museums in Paris, Bergen, Washington DC, Uppsala and at the University of Cape Town. Three students have been co-supervised by Delsett the last year, two of them working with data from the Natural History Museum in Copenhagen. The coming year three students will submit their theses, and three new students have been admitted for the last year of the project (2025-2026).

The most recent 300 million years of evolution of life on Earth has demonstrated the repeated evolution of fish-shaped marine predators. Vertebrate lineages have evolved fish-shaped bodies dozens of times, oftentimes from four-legged terrestrial ancestors. Of these, ichthyosaurs and whales evolved similar adaptations in response to environmental pressures, as one of the most classic examples of convergent evolution. Yet, we have been left to ponder the significance of evolutionary convergences. The ECHO project will address this by systematically quantifying the extent of convergence between the textbook example of whales and ichthyosaurs in feeding, locomotion and birth, on multiple scales. Drawing on the ECHO team’s expertise, we will deploy a novel methodological approach to study these two groups, leveraging ichthyosaur fossils collected in the Arctic, a large Scandinavian whale collection, and the world’s largest collection of whale fossils at the Smithsonian’s National Museum of Natural History. We will use data from the inside and outside of the skeletons, measuring size and shape of the bones that contribute to the streamlined body shape, to find out whether the evolutionary pathways were similar for the two groups. From the inside of skeletons, we will use CT scanning and actual thin sections to study the microstructure, which records ecology, growth and movements. This will enable us to find out when ichthyosaurs evolved live birth, and whether they grow in the same manner as whales. Just as society applies a cumulative understanding of history to frame and understand present day events, we need paleontological evidence to better understand present-day ecosystems. As 2/3 of the ocean is negatively impacted by human activity, it is increasingly obvious that more sustainable management is needed, and by using this case of convergent evolution to understand patterns in marine evolution, we aim to contribute to the new field of conservation paleobiology.