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Lower Cretaceous non-Marine
Turtles
In the Lower Cretaceous of Australia non-marine turtles have been
found to be reasonably common in a number of deposits such as the
Wonthaggi Formation, Victoria, from the Aptian and a number of other
sites of Albian age throughout eastern Australia. Indeterminate
cryptodires have been recovered from these sites, a characteristic of
which was retraction of the neck into the shell in a vertical fashion.
Chelycarapookus arctuatus was the smallest
known named species, about 200 mm long, from the Albian in the Merino
Group strata near Casterton in western Victoria. It was described from
an internal shell mould. Chelycarapookus, a
primitive turtle with a rounded shell similar to that of the sinemydids,
a group of Asian cryptodirans from the Cretaceous. The relationships of
this species is uncertain because the only known specimen is too poorly
preserved to allow a conclusive determination.
In the Eumeralla Formation at Dinosaur Cove in Victoria a specimen
of Otwayemys cunicularius
from the lower Albian, a second cryptodiran, about 20 % larger than
Chelycarapookus was found. It is known from the remains of
several individuals, a shell, fragments of a skull and vertebrae. It
has been suggested that Otwayemys may be
related to the meiolaniids, very large turtles with horns and a tail
club, that survived on the Australian mainland and surrounding islands
until a few thousand years ago. In the Griman Creek Formation at
Lightning Ridge what has been described as probably meiolaniid material
from the lower-middle Albian has been found, indicating an animal that
had a snout that was short and broad, claws that were hoof-like, and along
the margins of the carapace were prominent triangular projections. It
has been suggested that a very long evolutionary history, from the
Cretaceous to the Holocene, would be implied if it is confirmed that
Otwayemys and the specimens from Lightning Ridge
are meiolaniid relatives, and on the Australian continent a radiation of
primitive turtles during the Late Mesozoic that is unique.
Sources & Further reading
- Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in
Australia, Mesozoic life from the southern continent, CSIRO
Publishing.
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