Developing echolocation: distinctive patterns in the ontogeny of the tympanoperiotic complex in baleen and toothed whales (Cetacea)

Cetaceans (baleen and toothed whales) present a unique set of adaptations for life in water. Among other abilities, the two living groups can hear and produce different sound frequencies: baleen whales use low frequencies primarily for communication, while toothed whales acquired the ability to echolocate using high frequency sounds. Both groups exhibit modifications to the morphology of the ear bones (tympanic bulla and periotic) that closely track their behaviour and ecology. While the evolution of sound reception in whales is being thoroughly investigated, the changes in prenatal development (ontogeny) that generate these disparate ear bone morphologies remain mostly unknown. In this study, we characterize the ontogeny of the ear bones in Cetacea by looking at the progression of ossification and associated changes in morphology using a combination of traditional measurements and an innovative landmark-free method to quantify shape on a newly assembled 3D dataset spanning the ontogeny and phylogeny of extant Cetacea. We found that the two groups of Cetacea share some aspects of inner ear ontogeny, such as a common growth trajectory of the periotic. However, differences in ossification, allometry and growth trajectory, particularly in the tympanic bone, reflect their divergent inner ear morphology and hearing abilities.The data is uploaded as two zipped folders, one for the tympanic bulla and the other for the periotic. The GPSA software is available at https://morphlab.sc.fsu.edu/software/gpsa/ to repeat the analyses using the provided PLY files. Code to analyze the homologized points and ordination values obtained with the GPSA is provided in the following GitHub repository: https://doi.org/10.5281/zenodo.5534706 See the publication for further information. Funding provided by: H2020 Marie Skłodowska-Curie ActionsCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010665Award Number: 894584PLY files: A total of 75 specimens of Cetacea from 7 international museum collections, 28 Mysticeti (baleen whales) and 47 Odontoceti (toothed whales), spanning from embryos (50% total gestational length, n = 19), and postnatal specimens (neonates, juveniles and adults, n = 11). This unparalleled dataset has representatives of all four living mystictes families and of five of the 10 extant families of odontocetes. Data was collected using CT scanning and reconstructed in 3D using Avizo 2020.3. It was then processed in Geomagic Wrap 2017 to create shapes with uniform number of triangles to use in the GPSA analysis. GPSA results: Results of this analysis are also provided, including a text file that describes all procedures performed in the software. A separate text files describes the procedure used to obtain prototype shape. Additional information on the dataset collection, shape preparation and GPSA analyses are available in the publication connected to this dataset and its Supplementary materials