An Email Exchange Regarding

An Email Exchange Regarding "Vestigial" Pelvic Bones in Whales

by Jim Pamplin

Episode IV in the 1984 PBS mini-series Voyage of the Mimi, (still shown to public school students) has a young Ben Affleck visiting paleontologist Dr. Whitmore at the Smithsonian Institute’s Natural History Museum, to get the low down on whale evolution. Affleck is skeptical when the scientist tells him whales evolved from land animals, but is finally convinced by the overwhelming "evidence". After showing young Ben some marine mammal skulls, Whitmore takes him to a catwalk near the ceiling of a hanging Gray Whale skeleton display. “Pelvic bones” are seen suspended from the ceiling by thin cables, unattached to any other bones of the skeleton. Ben comments,

"Finally, Dr. Whitmore showed me something that really convinced me: pelvic bones. We have pelvic bones. All animals that walk have pelvic bones. The pelvis is where the hind legs attach to the body. Some whales, like this Gray, still have pelvic bones, even though the bones don't have any purpose now. There wouldn't be any reason to ever have a pelvis if you didn't ever have hind legs. And there wouldn't be any reason to have hind legs if you didn't want to walk on land."

Watching this program raised a question in my mind. If these bones are not attached to the backbone, what holds them in place? Bones are normally anchor points for skeletal muscle. What muscles, if any, attach to these bones? To find an answer, I went to Google.com and typed in "Ask a cetologist." I selected a website from the search results and asked the following:

What muscles are attached to the "pelvic" bones of whales? What are such muscles attached to at their other end? What function do the muscles serve? Are they used for reproduction?
Thank you in advance for any information and sources you might be able to share.

Sincerely,

Jim Pamplin

On June 10, 2003 I received the following reply from:

Phillip J. Clapham, Ph.D.,
Large Whale Biology Program
Northeast Fisheries Science Center
166 Water Street
Woods Hole, MA 025434, U.S.A.

tel. 508 495-2316
fax 508 495-2066
email: pclapham@whsun1.wh.whoi.edu

Hi
I'm forwarding this to an anatomy expert, Jim Mead at Smithsonian...
Phil Clapham

Wednesday, June 11, 2003, I received the following reply from:

James G. Mead, Ph.D.
Curator of Marine Mammals, MRC 108
National Museum of Natural History
Smithsonian Institution
P.O. Box 37012
Washington, DC 20013-7012
mead.james@nmnh.si.edu
(202) 357-1923
(202) 786-2979 fax

The pelvic bones of whales serve as attachments for the musculature associated with the penis in males and its homologue, the clitoris, in females. The muscle involved is known as the ischiocavernosus and is quite a powerful muscle in males. It serves as a retractor muscle for the penis in copulation and probably provides the base for lateral movements of the penis. The mechanisms of penile motion are not well understood in whales. The penis seems to be capable of a lot of independent motion, much like the trunk of an elephant. How much of this is mediated by the ischiocavernosus is not known.

In females the anatomical parts are smaller and more diffuse. I would imagine that there is something homologous to the perineal muscles in man and tetrapods, which affect the entire pelvic area - the clitoris, vagina and anus.

The pelvic rudiments also serve as origins for the ischiocaudalis muscle, which is a ventral muscle that inserts on the tips of the chevron bones of the spinal column and acts to flex the tail in normal locomotion.

The only anatomical works on the pelvis that I known of are in large whales and as follows:

Abel, Othenio 1908 Die Morpholgie der Huftbeinrudimente der Cetaceen. Denkshriften - Osterreichische Akademie der Wissenshaften, Mathematisch - Naturwissenshaftliche Klasse, Wein, 81:139-195.

Arvy, L. 1976 Some Critical Remarks on the Subject of the Cetacean 'Girdles'. Investigations on Cetacea, 7:179 -186,

Avry, L. 1979 The Abdominal Bones of Cetaceans. Investigations on Catacea, 10:215-227.

Hosakawa, H. 1951 On the pelvic cartilages of the Balaenoptera-foetuses, with remarks on the specifical and sexual difference. Scientific Reports of the Whales Research Institute, 5:5-15.

Howell, A. B. 1930 Aquatic Mammals. Charles C Thomas, Publisher, Baltimore, xii + 338 pp. [p. 302 - 309 deal with the pelvic limb in cetacea].

Lonnberg, E. 1910 The pelvic bones of some cetacea. Arkiv fo"r Zoologi, 7(10) :1-15.

Schulte, H. von W. 1916 Anatomy of a fetus of Balaenoptera borealis. Memoirs of the American Museum of Natural History, new series, 1 (6) : 389-502, pls xliii-lvii.

Struthers, J. 1881 On the bones, articulations and muscles of the rudimentary hind-limb of the Greenland right-whale (Balaena mysticetus). Journal of Anatomy and physiology, 5:141-176 (bones and joints), 301-321 (muscles), pls. XIV-XVII.

Struthers, J. 1889 Memoir on the anatomy of the humback whale Megatera longimana. Maclachlan and Stewart, Edinburgh, [iv] + 188 = [1], 6 pls. Reprinted from the Jouranl of Anatomy and Physiology, 1887-89.

Turner, W. 1870 On the sternum and ossa innominata of the Longniddry whale. Journal of Anatomy and Physiology, 4:271, ill.

Good luck with your inquiries.

__________________________________________________________________________________

So, then, young Ben Affleck’s conclusion,

“…Some whales, like this Gray, still have pelvic bones, even though the bones don't have any purpose now. There wouldn't be any reason to ever have a pelvis if you didn't ever have hind legs. And there wouldn't be any reason to have hind legs if you didn't want to walk on land,"

as represented in Episode IV of the 1984 PBS miniseries Voyages of the Mimi, appears to have been misguided. Not only do the “pelvic" bones serve a very useful purpose in reproduction, but they also function as anchor points for muscles used in swimming.

So much for vestigial bones in whales.

Nessie...?