[Taxacom] Australian turtles

Thu Dec 2 19:30:53 CST 2021

Scott - why do you have a working hypothesis for a narrow center of origin
(relative to the range of allopatric members of the clade) in the first
place? What theory or method leads you to that evolutionary model? What
precisely do you present as evidence?

John

On Thu, Dec 2, 2021 at 7:18 PM Scott Thomson <scott.thomson321 at gmail.com>
wrote:

> Oh sorry Michael,
>
> On your last point, I agree you need more evidence. The origin of the
> Chelidae in Argentina is a working hypothesis, based on many factors, not
> just the fossils, but paleoenvironments, vicariance events, etc. Myself and
> Argentinian paleos as well as several others have been discussing this
> alot. Its where we are at at present. It could change.
>
> Cheers Scott
>
> On Thu, Dec 2, 2021, 8:13 PM Scott Thomson <scott.thomson321 at gmail.com>
> wrote:
>
>> Well. Over the years as a paleo I have learnt that wishing for what could
>> have been preserved is fruitless. So you learn to work with what you have.
>>
>> As for fragmentary remains, if they cannot be identified how do you know
>> they are chelids. I have examined Cretaceous chelids in Lightning Ridge and
>> QM. They can be identified to genus and are clearly new species. The oldest
>> chelid I am aware of in Australia is a jawbone, clearly chelid and a new
>> genus and species. Though it is a long neck. I dont use Pan-Chelidae
>> because that grouping is poorly defined and missrepresents the
>> relationships of the family. What I have learnt is you cannot work on the
>> deep relationship's of this family without looking at Australian and South
>> American evolution together.
>>
>> Cheers Scott
>>
>> I
>>
>> On Thu, Dec 2, 2021, 7:44 PM Michael Heads <m.j.heads at gmail.com> wrote:
>>
>>> 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
>>>> >>> _______________________________________________
>>>> >>> Taxacom Mailing List
>>>> >>>
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>>>> >>> The Taxacom email archive back to 1992 can be searched at:
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>>>> >>>
>>>> >>> Nurturing nuance while assailing ambiguity for about 34 years,
>>>> 1987-2021.
>>>> >>>
>>>> >>
>>>> _______________________________________________
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>>>> You can reach the person managing the list at:
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>>>> The Taxacom email archive back to 1992 can be searched at:
>>>> http://taxacom.markmail.org
>>>>
>>>> Nurturing nuance while assailing ambiguity for about 34 years,
>>>> 1987-2021.
>>>>
>>>
>>>
>>> --
>>> 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>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>>