[Taxacom] Australian turtles

[Scott Thomson]

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
>>>>>>> >>> _______________________________________________
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>>>>>>> >>>
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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.
>>>>>>> >>>
>>>>>>> >>
>>>>>>> _______________________________________________
>>>>>>> Taxacom Mailing List
>>>>>>>
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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.
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> 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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