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Evolution of hyperphalangy and digit reduction in the cetacean manus
Lisa Noelle Cooper1, Annalisa Berta, Susan D Dawson
1Anatomy Department, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272-0095, USA. lisa1225@yahoo.com
Anatomical Record (Hoboken, N.J. : 2007)
|May 23, 2007
Summary
Whale and dolphin flipper evolution shows increased finger bones (hyperphalangy) and digit loss, influencing flipper shape for swimming and turning. This study traces these changes in cetacean forelimbs.
Area of Science:
- Marine Biology
- Paleontology
- Evolutionary Biology
Background:
- Cetaceans possess unique flippers with hyperphalangy (increased phalanges) and variable digit numbers.
- Toothed whales (odontocetes) are typically pentadactylous, while baleen whales (mysticetes) are often tetradactylous and lack metacarpals.
Purpose of the Study:
- To survey cetacean metacarpal and phalangeal morphology.
- To trace the evolutionary history of hyperphalangy within cetacean phylogeny.
- To test hypotheses regarding cetacean digit loss.
Main Methods:
- Dissections of 16 cetacean flippers from 10 species.
- Analysis of phalangeal count data from radiographs and osteological specimens.
- Phylogenetic optimization of morphological characters.
Main Results:
- Digital ray I is reduced or lost in many cetaceans, with complete loss in tetradactylous mysticetes around 14 million years ago.
- Hyperphalangy is most pronounced in digits II and III (odontocetes) and III and IV (mysticetes), evolving by 7-8 million years ago.
- Digit loss and positioning correlate with flipper shape, impacting swimming and turning capabilities.
Conclusions:
- Cetacean flipper morphology, including digit reduction and hyperphalangy, is shaped by evolutionary pressures related to locomotion.
- Flipper shape variations are linked to specific swimming and maneuvering strategies.
- Hyperphalangy may enhance hydrodynamic performance by distributing forces and smoothing the flipper's leading edge.
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