[Taxacom] Australian turtles

[Scott Thomson]

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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