Small mammals have big tails in the tropics

John Alroy*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Aim: The aim was to test whether large-scale patterns of variation in the bodily proportions of small mammals relate to latitude and climate. Location: The New World. Time period: Current. Major taxa studied: Marsupials, lipotyphlans and rodents. Methods: Distributional, morphological and phylogenetic data were compiled for 149 faunal samples including 360 species of New World small mammals. Phylogenetic autocorrelation was addressed using phylogenetic generalized least squares regression. Results: The faunal data show that tails are systematically larger in the tropics relative to head and body lengths. Furthermore, the data for individual species demonstrate a negative relationship between tail length and the distance of the midpoint of a geographical range from the equator. Hind foot and ear length also decline at high latitudes, but the relationships are much weaker. Allen's rule states that all extremities, including ears, feet and tails, should be larger at low latitudes because heat loss is not a limiting factor. However, no correlation between any measurement and mean annual temperature is found in two major groups (cricetid rodents and didelphid marsupials) or in all mammals combined. Main conclusions: Allen's rule does not apply at the macroevolutionary scale, and a new one does. Given that long tails stabilize movement between tree branches and are better suited for being prehensile, this rule might relate to increasing arboreality in the tropics.

Original languageEnglish
Pages (from-to)1042-1050
Number of pages9
JournalGlobal Ecology and Biogeography
Issue number8
Early online dateApr 2019
Publication statusPublished - Aug 2019


  • Allen's rule
  • ecomorphology
  • latitudinal gradients
  • macroecology
  • mammals
  • tail length


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