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RE: Floating allosaurs?? (sort of...)



At 02:01 PM 26/01/01 -0800, Nathan Myhrvold wrote:
That's interesting. It isn't at all what I had read - there was a recent
paper comparing DNA in Galapagos tortises to mainland species, which I
thought were more normal tortise sizes.   Do you have any references?

The paper you refer to is "Origin and evolutionary relationships of giant Galapagos tortoises" by
Adalgisa Caccone , James P. Gibbs, Valerio Ketmaier, Elizabeth Suatoni, and Jeffrey R. Powell, published in
Proc. Nat. Acad. Sci. 96: 13223?13228 (and available as a pdf file).  Though the paper found that the closest living relative of the Galapagos tortoises was G. chilensis, the smallest tortoise in South America today, it went on to say:

"Although G. chilensis is the closest living relative of the Galapagos tortoise, it is unlikely that the direct ancestor of G. nigra was a small-bodied tortoise. Several lines of reasoning (for review, see ref. 2) suggest that gigantism was a preadapted condition for successful colonization of remote oceanic islands,
rather than an evolutionary trend triggered by the insular environment. Giant tortoises colonized the Seychelles at least three separate times (29). Fossil giant tortoises are known from mainland South America, and morphological analysis of these and extant species are consistent with a clade containing giant tortoise fossils and
G. chilensis (30)."

I am also basing my comments on conversations with turtle biologists!

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com