[Taxacom] Australian turtles

Thu Dec 2 20:44:14 CST 2021

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:
>>>>>> >>> 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.
>>>>>> >>>
>>>>>> >>
>>>>>> _______________________________________________
>>>>>> 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>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>