What are the limits on whale ear bone size? Non-isometric scaling of the cetacean bulla

Sabrina L Groves; Carlos Mauricio Peredo; Nicholas D Pyenson

doi:10.7717/peerj.10882

What are the limits on whale ear bone size? Non-isometric scaling of the cetacean bulla

PeerJ. 2021 Feb 5:9:e10882. doi: 10.7717/peerj.10882. eCollection 2021.

Authors

Sabrina L Groves^{1

2}, Carlos Mauricio Peredo^{1

3

4}, Nicholas D Pyenson^{1

5}

Affiliations

¹ Department of Paleobiology, National Museum of Natural History, Washington, DC, USA.
² Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA.
³ Department of Earth and Environmental Science, University of Michigan - Ann Arbor, Ann Arbor, MI, USA.
⁴ Department of Marine Biology, Texas A&M University - Galveston, Galveston, TX, USA.
⁵ Department of Paleontology and Geology, Burke Museum of Natural History and Culture, Seattle, WA, USA.

Abstract

The history of cetaceans demonstrates dramatic macroevolutionary changes that have aided their transformation from terrestrial to obligate aquatic mammals. Their fossil record shows extensive anatomical modifications that facilitate life in a marine environment. To better understand the constraints on this transition, we examined the physical dimensions of the bony auditory complex, in relation to body size, for both living and extinct cetaceans. We compared the dimensions of the tympanic bulla, a conch-shaped ear bone unique to cetaceans, with bizygomatic width-a proxy for cetacean body size. Our results demonstrate that cetacean ears scale non-isometrically with body size, with about 70% of variation explained by increases in bizygomatic width. Our results, which encompass the breadth of the whale fossil record, size diversity, and taxonomic distribution, suggest that functional auditory capacity is constrained by congruent factors related to cranial morphology, as opposed to allometrically scaling with body size.

Keywords: Allometry; Bulla; Cetacean; Ear; Evolution; Mysticete; Odontocete; Scaling; Stem cetacean; Whale.

Grants and funding

Carlos Mauricio Peredo and Nicholas D. Pyenson were supported by the Remington Kellogg Fund and the Basis Foundation. Carlos Mauricio Peredo is further supported by National Science Foundation Award #1906181 and by the University of Michigan Society of Fellows. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.