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Convergent Evolution of Swimming Adaptations in Modern Whales Revealed by a Large Macrophagous Dolphin from the Oligocene of South Carolina.

Authors
  • Boessenecker, Robert W1
  • Churchill, Morgan2
  • Buchholtz, Emily A3
  • Beatty, Brian L4
  • Geisler, Jonathan H4
  • 1 Department of Geology and Environmental Geosciences, College of Charleston, Charleston, SC 29424, USA; University of California Museum of Paleontology, University of California, Berkeley, CA 94720, USA. Electronic address: [email protected]
  • 2 Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, WI 54901, USA.
  • 3 Department of Biological Sciences, Wellesley College, Wellesley, MA 02481, USA.
  • 4 Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA.
Type
Published Article
Journal
Current biology : CB
Publication Date
Aug 17, 2020
Volume
30
Issue
16
Identifiers
DOI: 10.1016/j.cub.2020.06.012
PMID: 32649912
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Modern whales and dolphins are superbly adapted for marine life, with tail flukes being a key innovation shared by all extant species. Some dolphins can exceed speeds of 50 km/h, a feat accomplished by thrusting the flukes while adjusting attack angle with their flippers [1]. These movements are driven by robust axial musculature anchored to a relatively rigid torso consisting of numerous short vertebrae, and controlled by hydrofoil-like flippers [2-7]. Eocene skeletons of whales illustrate the transition from semiaquatic to aquatic locomotion, including development of a fusiform body and reduction of hindlimbs [8-11], but the rarity of Oligocene whale skeletons [12, 13] has hampered efforts to understand the evolution of fluke-powered, but forelimb-controlled, locomotion. We report a nearly complete skeleton of the extinct large dolphin Ankylorhiza tiedemani comb. n. from the Oligocene of South Carolina, previously known only from a partial rostrum. Its forelimb is intermediate in morphology between stem cetaceans and extant taxa, whereas its axial skeleton displays incipient rigidity at the base of the tail with a flexible lumbar region. The position of Ankylorhiza near the base of the odontocete radiation implies that several postcranial specializations of extant cetaceans, including a shortened humerus, narrow peduncle, and loss of radial tuberosity, evolved convergently in odontocetes and mysticetes. Craniodental morphology, tooth wear, torso vertebral morphology, and body size all suggest that Ankylorhiza was a macrophagous predator that could swim relatively fast, indicating that it was one of the few extinct cetaceans to occupy a niche similar to that of killer whales. Copyright © 2020 Elsevier Inc. All rights reserved.

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