Pappochelys
Name:
Pappochelys
(Grandfather turtle).
Phonetic: Pap-po-kel-iss.
Named By: R. R. Schoch & H. -D.
Sues -2015.
Classification: Chordata, Reptilia,
Pantestudines.
Species: P. rosinae (type).
Diet: Uncertain.
Size: About 20 centimetres long.
Known locations: Germany - Erfurt Formation.
Time period: Ladinian of the Triassic.
Fossil representation: Almost complete individual.
With a holotype specimen only twenty centimetres long Pappochelys seems an unassuming little creature at first glance, however this genus may just revolutionise our construction of the turtle evolutionary family tree. Ever since evolution went from being theory to accepted and proven fact, naturalists have being trying to find the exact place for everything, and much of this time turtles have always been placed within the anapsid group of reptiles. This is because most turtles that were known at the beginning of this research had no skull openings other than what they needed for their eyes and nostrils.
As
time progressed however, more and more fossil forms began to be added
to the list, and some of these genera were observed to actually have
additional skull openings similar to the diapsid reptiles (lizards,
snakes, crocodiles, dinosaurs, etc). These observations
caused many palaeontologists to reconsider the old anapsid lineage
which was based more upon assumption. Furthermore, studies based
upon molecular data suggested that turtles really were descended from
diapsid reptiles as opposed to anapsids. However it takes time to
change a long established theory, and for the most part turtles still
superficially resembled anapsids, with no transitional forms to prove
otherwise. Then in 2015, Pappochelys was
described.
Scientists
don’t actually like to use the term ‘missing link’, they prefer
to say ‘transitional form’, but whatever you parlance,
Pappochelys is the first genus that offers to form
an evolutionary
link between developed turtles and diapsid ancestors. Pappochelys
represents a near perfect intermediate link between Odontochelys,
one
of the earliest confirmed turtles, and Eunotosaurus,
a genus of
reptile that lived during the Permian. Eunotosaurus
does display
special adaptations to its ribs which many researchers have interpreted
as a precursor to the development of a turtle shell, though other
researchers have said that it is merely a coincidence and that
Eunotosaurus was actually a parareptile. The
description of
Pappochelys however places Eunotosaurus
back into the frame as the
ancestral form of turtles. Aside from denoting a diapsid lineage for
turtles, the authors of the Pappochelys
description also suggested
that Pappochelys and other turtles lay within the
Lepidosauromorpha,
meaning that they are more closely related to lizards and snakes than
they are crocodiles and dinosaurs.
Pappochelys
was a small creature and the holotype fossils were recovered from what
appears to have been lake sediment. The bones of Pappochelys
also
show thickening which would have made them heavier and allow
Pappochelys to swim more easily under the water.
These all indicate
that Pappochelys was likely semi-aquatic.
Further reading
- A Middle Triassic stem-turtle and the evolution of the turtle body
plan. - Nature. - R. R. Schoch & H. -D. Sues
-2015.
- Microanatomy of the stem-turtle Pappochelys rosinae indicates a
predominantly fossorial mode of life and clarifies early steps in the
evolution of the shell. - Scientific Reports. 9 (1): 10430. - Rainer R.
Schoch, Nicole Klein, Torsten M. Scheyer & Hans-Dieter Sues -
2019.
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