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Re: Mesozoic turtle papers: Proterochersis + Bauruemys



Ben Creisler
bcreisler@gmail.com

When I checked the pdfs, they turned out to be only the abstract with
no other content. My apologies. These looked like legitimate full
papers from the website. I sent the post without reading the entire
article first (which is usually no problem). However, there is a
problem here. These appear to be advance abstracts for a July 15, 2015
turtle symposium, not articles, so they still may be of  interest but
not what I assumed they were.

On Fri, Feb 27, 2015 at 8:46 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
>
> Two new papers in PeerJ preprints:
>
> Tomasz Szczygielski (2015)
> New data on the oldest turtles: revision and reconsideration of
> Proterochersidae.
> PeerJ PrePrints 3:e1059
> doi: http://dx.doi.org/10.7287/peerj.preprints.858v1
> https://peerj.com/preprints/858/
>
> Background. The origin of turtles, their earliest evolution and the
> homologies of the elements building their shell are still enigmatic
> and remain an object of ongoing discussion and research. Although the
> oldest fully shelled turtle – Proterochersis robusta from the Lower
> Stubensandstein (Norian) of Germany – was described more than a
> century ago, until recently it was mostly ignored by researchers. This
> is surprising, not only because of its notable stratigraphic position,
> but also due to the critical significance of this taxon in two
> competing hypotheses of turtle interrelationships. The divergence time
> of two main branches of Testudines crown group depends on whether
> Proterochersis is a basal pleurodire or a stem turtle. Methods. A
> detailed study of the German material of Proterochersis and
> Murrhardtia was performed by the author and the available specimens
> were compared with still growing collection of proterochersid remains
> from the Norian location in Poręba (Poland). Results. Two
> controversial taxa from Germany, Proterochersis intermedia and
> Murrhardtia staeschei are proved to be the synonyms of P. robusta.
> Establishment of another two proterochersid taxa is proposed and new
> primitive postcranial characters are recognized, supporting the stem
> position of Proterochersidae on the turtle phylogenetic tree.
> Discussion. Two general hypotheses concerning the split time of
> Cryptodira and Pleurodira are functioning in the literature, and
> Proterochersis plays a crucial role in these considerations. According
> to traditional view, this taxon is the oldest side-necked turtle,
> based on the sutural connection between its pelvis and shell. Numerous
> recent analyses tended to allocate the Pleurodira much higher on the
> tree, resulting in stem position of Proterochersis, though such
> placement usually lacked a strong support. This was caused by an
> incompletness of Proterochersis material (only shells) and errors in
> interpretation of some characters. New data, gathered mostly from the
> Polish – much more complete and well preserved – specimens, supports
> the basal position of Proterochersidae and provides new insights in
> the ancestral structure of the turtle shell.
>
>
> ==
>
>
> Thiago F. Mariani & Pedro S. R. Romano (2015)
> Skull morphometrics of the Late Cretaceous side-necked turtle
> Bauruemys elegans (Pleurodira, Podocnemididae) from Presidente
> Prudente Formation, São Paulo, Brazil.
> PeerJ PrePrints 3:e1060
> doi:  http://dx.doi.org/10.7287/peerj.preprints.859v1
> https://peerj.com/preprints/859/
>
> Background. Previous quantitative studies about Bauruemys elegans
> (Suárez, 1969) shell variation, as well as the taphonomy
> interpretation of its type locality, have suggested that all specimens
> collected in this locality may have belonged to the same population.
> We rely on this hypothesis in a morphometric study of the skull. Also,
> we tried to assess the eating preference habits differentiation that
> might be explained as due to ontogenetic changes.Methods. We took 29
> linear measurements from 21 skulls of B. elegans. First, a Principal
> Components Analysis (PCA) was performed using 27 measurements
> (excluding total length and width characters) in order to plot the
> overall individual dispersion in PCs to visualize patterns of
> scattering based on the form variance. Secondly, PCA was carried out
> using ratios of length and width of each original measurement to
> assess shape variation among individuals. Finally, original
> measurements were log-transformed to describe allometries along the
> ontogenetic development.Results. The first three PCs of the first
> analysis comprising 70.2% of the variance. PC1 was related to size
> variation and all others related to shape variation. MCZ4123 and
> MN7071-V have been plotted outside the 95% ellipse in PC1xPC2 axes.
> The first three PCs of the second analysis comprising 64% of the
> variance. When considering PC1xPC2 and PC2xPC3, all specimens have
> been plotted inside the 95% ellipse, which is in contrast to PC1xPC3
> in which two individuals (MCT1753- R and MN6750-V) are outliers. In
> the third analysis, five measurements were positively allometric, 18
> were negatively allometric and four represent truly negatively
> allometry. All bones of the posterior and the lateral emarginations,
> as well as the squamosal, lengthen due to size increasing, different
> from the jugal and the quadratojugal which decrease in
> width.Discussion. Some specimens show small differences in form
> (MCZ4123 and MN7071-V) and shape (MCT1753-R and MN6750-V). Form
> differences were already detected in a shell morphometry study, but
> interpreted as due to ontogeny, which might be the case of the present
> data. Moreover, all outlier specimens are crushed and/or distorted,
> thus the form/shape differences might be partially due to taphonomy.
> The allometric lengthen of parietal, quadrate, squamosal, maxilla,
> associated with the narrowing of jugal and quadratojugal may be
> related to changes in feeding habit between different stages of
> development. This change in shape might represent a progressive skull
> stretching and enlargement of posterior and lateral emargination
> during ontogeny, and consequently, the increment of the
> feeding-apparatus musculature. Smaller individuals may have fed of
> softer diet whereas bigger ones probably have had a harder diet, as
> seen in some living species of Podocnemis. We conclude that the skull
> variation is higher than expected and might be related to differences
> in feeding habits along the ontogeny of B. elegans.