DOI: 10.6086/d1r69c
title: Developing echolocation: distinctive patterns in the ontogeny of the tympanoperiotic complex in baleen and toothed whales (Cetacea)

description: 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.
description: PLY 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
 (&lt;2 months from conception) to adults are analysed in this study
 for the tympanic bulla. As the periotic starts ossifying in later stages
 of gestation [9, 10], only 46 of these specimens could be used for
 analyses of this element. Specimens were binned into embryos or early
 fetuses (estimated age &lt;50% total gestational length, n = 45), late
 fetuses (&gt;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.
description: 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.