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Mesozoic turtle papers: Proterochersis and Hylaeochelys



From: Ben Creisler
bcreisler@gmail.com

Two recent papers about turtles that may be of interest:


In open access:

Walter G Joyce, Rainer R Schoch and Tyler R Lyson (2013)
The girdles of the oldest fossil turtle, Proterochersis robusta, and
the age of the turtle crown.
BMC Evolutionary Biology 2013, 13:266
doi:10.1186/1471-2148-13-266
http://www.biomedcentral.com/1471-2148/13/266/abstract
http://www.biomedcentral.com/content/pdf/1471-2148-13-266.pdf


Abstract (provisional)
Background
Proterochersis robusta from the Late Triassic (Middle Norian) of
Germany is the oldest known fossil turtle (i.e. amniote with a fully
formed turtle shell), but little is known about its anatomy. A newly
prepared, historic specimen provides novel insights into the
morphology of the girdles and vertebral column of this taxon and the
opportunity to reassess its phylogenetic position.

Results
The anatomy of the pectoral girdle of P. robusta is similar to that of
other primitive turtles, including the Late Triassic (Carnian)
Proganochelys quenstedti, in having a vertically oriented scapula, a
large coracoid foramen, a short acromion process, and bony ridges that
connect the acromion process with the dorsal process, glenoid, and
coracoid, and by being able to rotate along a vertical axis. The
pelvic elements are expanded distally and suturally attached to the
shell, but in contrast to modern pleurodiran turtles the pelvis is
associated with the sacral ribs.

Conclusions
The primary homology of the character "sutured pelvis" is
unproblematic between P. robusta and extant pleurodires. However,
integration of all new observations into the most complete
phylogenetic analysis that support the pleurodiran nature of P.
robusta reveals that this taxon is more parsimoniously placed along
the phylogenetic stem of crown Testudines. All current phylogenetic
hypotheses therefore support the basal placement of this taxon, imply
that the sutured pelvis of this taxon developed independently from
that of pleurodires, and conclude that the age of the turtle crown is
Middle Jurassic.

===

Adán Pérez-García & Francisco Ortega (2013)
A new species of the turtle Hylaeochelys (Eucryptodira) outside its
known geographic and stratigraphic ranges of distribution.
Comptes Rendus Palevol (advance online publication)
doi: http://dx.doi.org/10.1016/j.crpv.2013.10.009
http://www.sciencedirect.com/science/article/pii/S1631068313001723


A relatively complete shell of a turtle, recently found in the
Tithonian (Freixial Formation) of the Lusitanian Basin (Portugal), is
presented and described here. Its taxonomic adscription and systematic
position are discussed in this paper. This turtle is identified as a
basal member of Eucryptodira. Other basal representatives of this
group, all of them attributed to Plesiochelyidae, had previously been
recognized in this Formation. The new specimen cannot be assigned to
that family. It is recognized as a member of the genus Hylaeochelys.
The presence of Hylaeochelys had been, so far, only confirmed in Early
Cretaceous levels of England. Therefore, this finding expands both the
range of geographic distribution of the genus and its stratigraphic
distribution. The new specimen is attributed to a new species of this
so far monospecific taxon: Hylaeochelys kappa sp. nov.