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Evolution of long necks (sauropods, pterosaurs, plesiosaurs, etc.)



From: Ben Creisler
bscreisler@yahoo.com
 
A new paper not yet mentioned on the DML:
 
 Wilkinson, D. M. and Ruxton, G. D. (2011) 
Understanding selection for long necks in different taxa. 
Biological Reviews (advance online publication) 
doi: 10.1111/j.1469-185X.2011.00212.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-185X.2011.00212.x/abstract
 
 
 
 There has been recent discussion about the evolutionary pressures underlying 
the long necks of extant giraffes and extinct sauropod dinosaurs. Here we 
summarise these debates and place them in a wider taxonomic context. We 
consider the evolution of long necks across a wide range of (both living and 
extinct) taxa and ask whether there has been a common selective factor or 
whether each case has a separate explanation. We conclude that in most cases 
long necks can be explained in terms of foraging requirements, and that 
alternative explanations in terms of sexual selection, thermoregulation and 
predation pressure are not as well supported. Specifically, in giraffe, 
tortoises, and perhaps sauropods there is likely to have been selection for 
high browsing. It the last case there may also have been selection for reaching 
otherwise inaccessible aquatic plants or for increasing the energetic 
efficiency of low browsing. For camels, wading birds and ratites,
 original selection was likely for increased leg length, with correlated 
selection for a longer neck to allow feeding and drinking at or near substrate 
level. For fish-eating long-necked birds and plesiosaurs a small head at the 
end of a long neck allows fast acceleration of the mouth to allow capture of 
elusive prey. A swan's long neck allows access to benthic vegetation, for 
vultures the long neck allows reaching deep into a carcass. Geese may be an 
unusual case where anti-predator vigilance is important, but so may be 
energetically efficient low browsing. The one group for which we feel unable to 
draw firm conclusions are the pterosaurs, this is in keeping with the current 
uncertainty about the biology of this group. Despite foraging emerging as a 
dominant theme in selection for long necks, for almost every taxonomic group we 
have identified useful empirical work that would increase understanding of the 
selective costs and benefits of a long neck.