[Taxacom] Australian turtles

[John Grehan]

Hi Scott, if you do not work from a center of origin model for allopatry I
guess I am confused as to why you used that model to explain an
Australia-South America distribution. Can you clarify please?

John

On Thu, Dec 2, 2021 at 9:57 PM Scott Thomson <scott.thomson321 at gmail.com>
wrote:

> I do not work from that premise as a model, I do not think it explains all
> of the distribution of the Chelids. I think it may be applicable to the
> early radiation of this family but its subsequent radiations have other
> factors .
>
> At present I am determining the groups relationships, not all the data is
> in. Not all the modern species are even described. Testing hypotheses on
> how they radiated comes later. So as I said it may change I could be wrong.
>
> Cheers Scott
>
> On Thu, Dec 2, 2021, 10:44 PM John Grehan <calabar.john at gmail.com> wrote:
>
>> So are you saying that you work from the premise that allopatric
>> distributions of a clade result from a sequential spread of ancestors from
>> a more restricted distribution range and that the location of the oldest
>> fossil marks or approximates that narrower center of origin? If so, what
>> leads you to that model?
>>
>> On Thu, Dec 2, 2021 at 9:32 PM Scott Thomson <scott.thomson321 at gmail.com>
>> wrote:
>>
>>> Its a working hypothesis, if evidence comes its wrong it will change.
>>>
>>> At present there are no stem chelids from outside southern South
>>> America. The modern allopatric populations are all crown chelids. Even the
>>> older ones from Australia. This has been a successful group that radiated
>>> significantly since the Eocene.
>>>
>>> Weaknesses in what I am saying is that there are very few Cretaceous
>>> sites in Brasil, most of them are to the north and have no Chelids. Same
>>> goes for Colombia. Cainozoic sites have Chelids but are too young.
>>>
>>> In Australia there are also few Cretaceous sites relevant to Chelids,
>>> those that exist are poorly described. So better work may uncover
>>> information that could change this. But most cheid fossils in Australia are
>>> modern genera.
>>>
>>> So in the end its the best explanation of the available data, right now.
>>>
>>> Chelids are unusual, most turtle families have large distributions
>>> geographically. Chelids seem to have been very restricted and have a
>>> significant number of fossils, so this is not an effort to make pedictions
>>> of ghost lineages.
>>>
>>> For Emydids or Testudinids this is far more difficult and the
>>> paleozoogeography of Podocnemidae and Trionychidae is very complex for
>>> example.
>>>
>>> As a caveat when I say Argentina for example I am pinning it on the
>>> fossils that support this, the area of early evolution of the family no
>>> doubt included southern Brasil, but preservation there is Cainozoic, but
>>> that is speculation.
>>>
>>> Cheers Scott
>>>
>>> On Thu, Dec 2, 2021, 9:31 PM John Grehan <calabar.john at gmail.com> wrote:
>>>
>>>> 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
>>>>>>>> >>>
>>>>>>>> >>> Send Taxacom mailing list submissions to:
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>>>>>>>> >>> For list information; to subscribe or unsubscribe, visit:
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>>>>>>>> >>> You can reach the person managing the list at:
>>>>>>>> >>> taxacom-owner at mailman.nhm.ku.edu
>>>>>>>> >>> 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.
>>>>>>>> >>>
>>>>>>>> >>
>>>>>>>> _______________________________________________
>>>>>>>> Taxacom Mailing List
>>>>>>>>
>>>>>>>> Send Taxacom mailing list submissions to:
>>>>>>>> taxacom at mailman.nhm.ku.edu
>>>>>>>> For list information; to subscribe or unsubscribe, visit:
>>>>>>>> http://mailman.nhm.ku.edu/cgi-bin/mailman/listinfo/taxacom
>>>>>>>> You can reach the person managing the list at:
>>>>>>>> taxacom-owner at mailman.nhm.ku.edu
>>>>>>>> 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>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>