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Updated: May 23, 2025

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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River dolphin cochlea has not evolved convergently.

Mariana Viglino1, Travis Park2,3,4

  • 1Instituto Patagónico de Geología y Paleontología, Puerto Madryn, Chubut, Argentina.

Biology Letters
|May 20, 2025
PubMed
Summary

River dolphins do not show convergent evolution in their cochlear morphology. Instead, variations in sound production structures likely helped them adapt to challenging riverine environments.

Keywords:
CetaceaOdontocetiecholocationevolutioninner eartoothed whales

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Area of Science:

  • Evolutionary biology
  • Comparative anatomy
  • Marine biology

Background:

  • River dolphins (Cetacea, Odontoceti) inhabit complex, threatened aquatic environments.
  • Echolocation is crucial for river dolphin survival, and cochlear morphology reflects hearing and echolocation capabilities.
  • Previous studies on river dolphin cochleae lacked comprehensive taxonomic representation, potentially hindering evolutionary insights.

Purpose of the Study:

  • To investigate convergent evolution in cochlear morphology among river dolphins.
  • To include all extant and extinct riverine taxa in a broader evolutionary framework.
  • To analyze cochlear morphology using an inclusive definition of river dolphins.

Main Methods:

  • Generation of three-dimensional models from micro-CT scans of cochleae.
  • Comparative analysis of cochlear morphology across diverse river dolphin species, including extinct taxa.
  • Statistical evaluation to test for convergence and evolutionary patterns.

Main Results:

  • River dolphin cochleae are not significantly different from those of marine cetaceans.
  • Greater interspecific morphological variability was observed in river dolphin cochleae than anticipated.
  • Statistical analyses confirmed a lack of cochlear convergence in river dolphins.

Conclusions:

  • Evolutionary adaptations in river dolphins are not driven by cochlear convergence.
  • Other ecological factors and sound production apparatus (e.g., skull shape, melon) are more influential in shaping river dolphin evolution.
  • The study reframes understanding of river dolphin adaptation to their unique habitats.