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Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix
Author(s) -
SMITH H. F.,
FISHER R. E.,
EVERETT M. L.,
THOMAS A. D.,
RANDAL BOLLINGER R.,
PARKER W.
Publication year - 2009
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/j.1420-9101.2009.01809.x
Subject(s) - appendix , biology , phylogenetic tree , cladistics , phylogenetics , evolutionary biology , zoology , function (biology) , paleontology , genetics , gene
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.