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

John Grehan calabar.john at gmail.com
Sun Jul 7 20:34:07 CDT 2019


Hi Ken,

But of course "they did not suggest such tortoises rafted around the tip of
South America". That is what I said. Well Caccone et al were a bit vague as
to how chilensis, which is to the east of the Andes, made it to the other
side to hop on a raft to the Humboldt current. Admittedly they did not say
anything about how they reached the current from the east side of the
Andes. Maybe the hiked over the mountains (although they are elevationally
challenged). If Caccone et al did mean it to raft all the way (and they did
not indicate otherwise) then going around the Horn of South America seemed
the option, although admittedly they could have rafted across the Indian
Ocean and Pacific. So agreed, I was inferring what proceeding event was
implied by Caccone et al. Its a pity they were not explicit about the
origin of the Humboldt ride. That might have made for some imaginative
reading.

Thanks for the added info about the fossil. Most appreciated. I will
acknowledge your assistance in an article addressing this taxon.

John Grehan

On Sun, Jul 7, 2019 at 9:12 PM Kenneth Kinman via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> 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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