Convergent evolution of forelimb-propelled swimming in seals

Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true seals (phocids) propelling themselves primarily with their hindlimbs, whereas eared seals (otariids) rely on their wing-like foreflippers. 1 , 2 Current explanations of this functional dichotomy invoke...

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Bibliographic Details
Published in:Current Biology
Main Authors: Hocking, David P., Marx, Felix G., Wang, Shibo, Burton, David, Thompson, Mark, Park, Travis, Burville, Ben, Richards, Hazel L., Sattler, Renae, Robbins, James, Miguez, Roberto Portela, Fitzgerald, Erich M. G., Slip, David J., Evans, Alistair R.
Format: Article in Journal/Newspaper
Language:English
Published: 2021
Subjects:
hydrodynamics
computational fluid dynamics
Pinnipedia
Otariidae
Phocidae
Monachinae
flippers
anatomy
Leopard Seals
Online Access:https://researchers.mq.edu.au/en/publications/f73abc57-00aa-483a-8f0a-904f8d1ba933
https://doi.org/10.1016/j.cub.2021.03.019
http://www.scopus.com/inward/record.url?scp=85107301303&partnerID=8YFLogxK
http://purl.org/au-research/grants/arc/LP150100403
http://purl.org/au-research/grants/arc/DP180101797
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Summary:Modern pinnipeds (true and eared seals) employ two radically different swimming styles, with true seals (phocids) propelling themselves primarily with their hindlimbs, whereas eared seals (otariids) rely on their wing-like foreflippers. 1 , 2 Current explanations of this functional dichotomy invoke either pinniped diphyly 3–5 or independent colonizations of the ocean by related but still largely terrestrial ancestors. 6–8 Here, we show that pinniped swimming styles form an anatomical, functional, and behavioral continuum, within which adaptations for forelimb swimming can arise directly from a hindlimb-propelled bauplan. Within phocids, southern seals (monachines) show a convergent trend toward wing-like, hydrodynamically efficient forelimbs used for propulsion during slow swimming, turning, bursts of speed, or when initiating movement. This condition is most evident in leopard seals, which have well-integrated foreflippers with little digit mobility, reduced claws, and hydrodynamic characteristics comparable to those of forelimb-propelled otariids. Using monachines as a model, we suggest that the last common ancestor of modern seals may have been hindlimb-propelled and aquatically adapted, thus resolving the apparent contradiction at the root of pinniped evolution.

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