Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix

H. F. Smith, R. E. Fisher, M. L. Everett, A. D. Thomas, R. Randal Bollinger, W. Parker

Research output: Contribution to journalArticlepeer-review

94 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)1984-1999
Number of pages16
JournalJournal of Evolutionary Biology
Issue number10
StatePublished - Oct 2009


  • Appendix
  • Cecum
  • Cladistic
  • Lagomorphs
  • Marsupials
  • Morphology
  • Parsimony
  • Primates
  • Rodents
  • Vermiform

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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