Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix |
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| Authors: | H. F. SMITH R. E. FISHER M. L. EVERETT A. D. THOMAS R. RANDAL BOLLINGER W. PARKER |
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| Affiliation: | 1. Department of Basic Medical Sciences, University of Arizona College of Medicine‐Phoenix, in Partnership with Arizona State University, Phoenix, AZ, USA;2. Present address: Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ, USA.;3. School of Life Sciences, Arizona State University, Tempe, AZ, USA;4. Department of Surgery, Duke University Medical Center, Durham, NC, USA;5. Department of Immunology, Duke University, Durham, NC, USA |
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| 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. |
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| Keywords: | appendix cecum cladistic lagomorphs marsupials morphology parsimony primates rodents vermiform |
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