Present address: Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ, USA.
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Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix
Article first published online: 12 AUG 2009
DOI: 10.1111/j.1420-9101.2009.01809.x
© 2009 The Authors. Journal Compilation © 2009 European Society For Evolutionary Biology
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How to Cite
SMITH, H. F., FISHER, R. E., EVERETT, M. L., THOMAS, A. D., RANDAL BOLLINGER, R. and PARKER, W. (2009), Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix. Journal of Evolutionary Biology, 22: 1984–1999. doi: 10.1111/j.1420-9101.2009.01809.x
Publication History
- Issue published online: 14 SEP 2009
- Article first published online: 12 AUG 2009
- Received 3 May 2009; revised 14 June 2009; accepted 19 June 2009
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Keywords:
- appendix;
- cecum;
- cladistic;
- lagomorphs;
- marsupials;
- morphology;
- parsimony;
- primates;
- rodents;
- vermiform
Abstract
A recently improved understanding of gut immunity has merged with current thinking in biological and medical science, pointing to an apparent function of the mammalian cecal appendix as a safe-house for symbiotic gut microbes, preserving the flora during times of gastrointestinal infection in societies without modern medicine. This function is potentially a selective force for the evolution and maintenance of the appendix, and provides an impetus for reassessment of the evolution of the appendix. A comparative anatomical approach reveals three apparent morphotypes of the cecal appendix, as well as appendix-like structures in some species that lack a true cecal appendix. Cladistic analyses indicate that the appendix has evolved independently at least twice (at least once in diprotodont marsupials and at least once in Euarchontoglires), shows a highly significant (P < 0.0001) phylogenetic signal in its distribution, and has been maintained in mammalian evolution for 80 million years or longer.