[Taxacom] Australian turtles

Thu Dec 2 17:44:26 CST 2021

Hi Scott,

You wrote: 'With turtles we have a major advantage over a lot of groups,
they fossilise really well. The shell is very hard, so if it is a
depositional environment
and turtles were there there will always be turtle fossils'. But not if the
fossiliferous rocks have been removed by erosion or metamorphosed. Or the
fossils may just be too fragmentary to identify properly, as with the
Australian fossil 'pan-chelids' from Early Cretaceous.

Also, just because a group has it's sister in area X doesn't mean that that
is the centre of origin.

On Fri, Dec 3, 2021 at 11:11 AM Scott Thomson via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> The Chelids are related to the Araripemyidae as I said. That family is only
> found in South America and the oldest chelids are also from those beds.
>
> With turtles we have a major advantage over alot of groups, they fossilise
> really well. The shell is very hard, so if it is a depositional environment
> and turtles were there there will always be turtle fossils. There are 1200
> odd species of fossil turtles compared to 357 living ones.
>
> So yes in turtles the known stratigraphic setting has bearing. Could they
> have been elsewhere sure, but generally if they were we would have found
> them. So what I am saying is based on physical existing evidence.
>
> Cheers Scott
>
> On Thu, Dec 2, 2021, 5:56 PM John Grehan <calabar.john at gmail.com> wrote:
>
> > Thanks for that update Scott.  You say that "When looking at
> relationships
> > of the Chelidae they clearly arose in South America" - how do
> relationships
> > determine that?
> >
> > You also note that "the oldest Chelid fossils being from Argentina." Are
> > you saying that the location of the oldest fossil has something to do
> with
> > a taxon being there longest?
> >
> > Cheers, John
> >
> > On Thu, Dec 2, 2021 at 4:48 PM Scott Thomson <scott.thomson321 at gmail.com
> >
> > wrote:
> >
> >> The Georges and Thomson 2010 paper is now 11 years old and significant
> >> work has been done since. The 2021 TTWG checklist will give a better
> >> appreciation of species.
> >>
> >> When looking at relationships of the Chelidae they clearly arose in
> South
> >> America, the oldest Chelid fossils being from Argentina. My own view is
> the
> >> evolved from the Araripemidae an extinct group of Pelomedusoides
> turtle. So
> >> although their modern sister group is the living Pelomedusoides,
> >> Podocnemidae and Pelomedusidae that arrangemt is honestly paraphyletic
> and
> >> Chelids should be considered Pelomedusoides along with the other
> families.
> >> Most people think of Chelids backwards by the way, short necks evolved
> from
> >> long necks not the other way around. Araripemys was a long neck. The
> split
> >> occurred Cretaceous at the latest, Aptian.
> >>
> >> Geographically they evolved in South America and spread through
> >> Antarctica to Australia. The are fossils of turtles from Antarctica
> >> believed to be Pleurodiran. I have not examined but I would hazard they
> are
> >> Chelids. So Gondwannan yes but southern Gondwannan. There movement into
> the
> >> tropics of South America and Australia is only recent, last 40 million
> >> years. They remain the most cold resilient freshwater turtle families.
> So
> >> when I show the distribution of the Chelidae you need to centre the
> earth
> >> on Antarctica to understand their distribution. Chelids are salt
> >> intolerant, sea water is a barrier for them. No fossils of Chelids have
> >> been found outside of southern Gondwanna.
> >>
> >> Trionychididae are sister to the Carettochelyidae and both groups are
> >> ancient going back to early Cretaceous with world eide distributions.
> Their
> >> group the Trionychoidea are sister to all other Cryptodirous turtles the
> >> split probably goes back to the Jurassic. The Trionychoidea are salt
> >> tolerant and even now can be found in open ocean. There are fossil
> >> Trionychids in Australia. Carettochelyidae may only have one modern
> species
> >> but it has 20 described species in 4 genera.
> >>
> >> The genus Natator like a lot of sea turtles is just another species of
> >> Chelonia. Sea turtles suffer both taxonomic inflation and taxonomic
> >> inertia. Sinking sea turtle taxa is almost impossible due to their high
> >> profile. Only one species of sea turtle has been sunk in 100 years
> Chelonia
> >> agassizi, even that is still argued about. So Natator is of course
> syster
> >> to C. mydas and should be in the same genus. Modern Sea turtles are
> only 70
> >> million years old, not that old for turtles.
> >>
> >> Hard thing with turtles is they disobey many assumptions, basically
> >> because they had time. The Triassic and KT extinction knocked off a lot
> of
> >> species but they got through both fine. The oldest turtles are now back
> to
> >> 240mya so lets call that 1/4 of a billion cause that is a soft maximum,
> its
> >> from China, specimens of similar age are found in Europe and Africa. So
> in
> >> all likely hood turtles have had a world wide existance since just after
> >> the first amniotes appeard. I consider them the most successful amniote,
> >> they were there at the beginning or shortly after, still here now.
> >>
> >> Cheers Scott
> >>
> >>
> >> On Thu, Dec 2, 2021, 4:35 PM John Grehan via Taxacom <
> >> taxacom at mailman.nhm.ku.edu> wrote:
> >>
> >>> Scott - turtles are not a group I have studied, but in a quick glancing
> >>> look at Georges & Thomson (2010) I note:
> >>>
> >>> "Trionychidae  30 living species in North America, Africa, Asia, and
> >>> New Guinea." Interesting range. Does that include Madagascar? What is
> the
> >>> sister group?
> >>>
> >>> "Chelidae.Australia, New Guinea, Timor and Roti ...South America. This
> is
> >>> said to be of " of undisputed Gondwanan origin", but is it? What we
> have
> >>> seems to be a circum-Pacific range rather than one including core
> >>> Gondwana
> >>> (e.g. Africa, India, Madagascar. What is the sister group?
> >>>
> >>> Heads (2014) notes that the sea turtles Natator that breeds along the
> >>> coast
> >>> of northern Australia has a sister group, Chelonia, that has a
> worldwide
> >>> distribution. Heads suggests that as with Arhemia (plant genus) and its
> >>> relatives, the distribution is consistent with early vicariance of
> >>> widespread ancestors at breaks around the Arafura and Coral Seas.
> >>>
> >>> By the way, (2010) is a very nice overview, but I would selfishly have
> >>> liked to have seen distribution maps for each taxon. That would have
> made
> >>> the paper much easier to assimilate for the biogeographer where
> locations
> >>> are recognized as informative. Perhaps something to keep in mind in the
> >>> future please? (if RepFocus has the ranges illustrated then not such a
> >>> problem, but it is nice when one can cite a publication source
> directly).
> >>>
> >>> Cheers, John
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> >>>
> >>
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-- 
Dunedin, New Zealand.

My books:

*Biogeography and evolution in New Zealand. *Taylor and Francis/CRC, Boca
Raton FL. 2017.
https://www.routledge.com/Biogeography-and-Evolution-in-New-Zealand/Heads/p/book/9781498751872

*Biogeography of Australasia:  A molecular analysis*. Cambridge University
Press, Cambridge. 2014. www.cambridge.org/9781107041028

*Molecular panbiogeography of the tropics. *University of California Press,
Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968

*Panbiogeography: Tracking the history of life*. Oxford University Press,
New York. 1999. (With R. Craw and J. Grehan).
http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC
<http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&source=gbs_navlinks_s>