[Taxacom] Your straw man argument (was: Galapagos tortoise bedtime story)

Kenneth Kinman kinman at hotmail.com
Sun Jul 7 20:12:19 CDT 2019


John,
        Well, it's easy to argue against a "straw man" that doesn't exist and then label it a bedtime story.   They did not suggest such tortoises rafted around the tip of South America, so you're arguing against something that they didn't say.   It is perfectly reasonable to suggest that one or more such rafts did ride the Humboldt Current from the mainland of western South America.
         I did some more checking, and it seems likely that the Miocene species Ch. gringorum of Patagonia gave rise not only to Ch. chilensis east of the Andes, but also to the early ancestors of the Galapagos tortoises to the west of the Andes.  The Strait of Magellan had absolutely nothing to do with it (and they did not suggest that it did).  It is interesting that Ch. gringorum may have also given rise to (or was basal to) other species of the genus as well.  I would suggest you read that paper (quote and weblink below):

A 2017 Conference paper says:
"Chelonoidis gringorum (Simpson, 1942) is a medium-sized testudinid taxon known mainly from the Early-Middle Miocene of Patagonia. Most fossil specimens come from the deposits in the area of Trelew – Gaiman – Dolavon (Chubut Province, Argentina). Besides the type material (a partial shell), several specimens have been referred to Ch. gringorum over the years, constituting the best-known fossil testudinid species in South America. Most phylogenetic analyses place Ch. gringorum as basal to the extant clade that includes Ch. chilensis and the Galápagos tortoises, or as basal to all extant species of Chelonoidis."

https://www.researchgate.net/publication/321289805_Chelonoidis_gringorum_unshelled_a_state-of-the-art_of_the_southernmost_tortoises_of_the_world


________________________________
From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of John Grehan via Taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Sunday, July 7, 2019 12:06 PM
To: taxacom
Subject: [Taxacom] Galapagos tortoise bedtime story

Here's another for those who believe in such things. Caccone et al 1999
found that the sister group to the Galapagos tortoise is Chelonoidis
chilensis. This species is distributed east of the Andes mostly in
Argentina (north of the Patagonia) and Bolivia. The only tortoise in the
genus that is on the Pacific Coast is C. carbonarius (Panama). Caccone et
al attribute the origin of the Galapagos tortoise to the Humboldt current,
but left out the more difficult question of how the tortoises found large
enough rafts (if such things could be produced in the scrublands or dry
forest habitats) that would remain stable enough to navigate around the tip
of South America, presumably via the Strait of Magellan, and AGAINST the
Cape Horn and Circumpolar Currents. Its wonder they didn't end up in South
Africa. Believe it or not.

John Grehan
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