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First published online March 14, 2008
Journal of Experimental Biology 211, 1141-1147 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.015339

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Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (Alligator mississippiensis)

T. J. Uriona and C. G. Farmer

Department of Biology, 257 South 1400 East, University of Utah, Salt Lake City, UT 84112, USA

e-mails: uriona{at}biology.utah.edu; farmer{at}biology.utah.edu

Accepted 4 February 2008

We used electromyography on juvenile American alligators to test the hypothesis that the following muscles, which are known to play a role in respiration, are recruited for aquatic locomotion: M. diaphragmaticus, M. ischiopubis, M. rectus abdominis, M. intercostalis internus, and the M. transversus abdominis. We found no activity with locomotion in the transversus. The diaphragmaticus, ischiopubis, rectus abdominis and internal intercostals were active when the animals executed a head-down dive from a horizontal posture. Weights attached to the base of the tail resulted in greater electrical activity of diaphragmaticus, ischiopubis and rectus muscles than when weights were attached to the head, supporting a role of this musculature in locomotion. The diaphragmaticus and rectus abdominis were active unilaterally with rolling maneuvers. Although the function of these muscles in locomotion has previously been unrecognized, these data raise the possibility that the locomotor function arose when Crocodylomorpha assumed a semi-aquatic existence and that the musculoskeletal complex was secondarily recruited to supplement ventilation.

Key words: pitch, roll, aquatic locomotion, lung, alligator, Alligator mississippiensis, archosaur, crocodilian, diaphragm, diaphragmaticus, ischiopubis, rectus abdominis, intercostalis, buoyancy, metacentric height, evolution, ventilation, ventilatory mechanics, pelvic aspiration