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Jurassic turtles from France and Switzerland + early tetrapod locomotion (free pdfs)



From: Ben Creisler
bcreisler@gmail.com

A new non-dino paper in open-access PeerJ:


Jérémy Anquetin, Christian Püntener & Jean-Paul Billon-Bruyat (2014)
A taxonomic review of the Late Jurassic eucryptodiran turtles from the
Jura Mountains (Switzerland and France).
PeerJ 2:e369
http://dx.doi.org/10.7717/peerj.369
https://peerj.com/articles/369/


Background. Eucryptodiran turtles from the Late Jurassic (mainly
Kimmeridgian) deposits of the Jura Mountains (Switzerland and France)
are among the earliest named species traditionally referred to the
Plesiochelyidae, Thalassemydidae, and Eurysternidae. As such, they are
a reference for the study of Late Jurassic eucryptodires at the
European scale. Fifteen species and four genera have been typified
based on material from the Late Jurassic of the Jura Mountains. In the
past 50 years, diverging taxonomic reassessments have been proposed
for these turtles with little agreement in sight. In addition, there
has been a shift of focus from shell to cranial anatomy in the past
forty years, although most of these species are only represented by
shell material. As a result, the taxonomic status of many of these 15
species remains ambiguous, which prevents comprehensive comparison of
Late Jurassic turtle assemblages throughout Europe and hinders
description of new discoveries, such as the new assemblage recently
unearthed in the vicinity of Porrentruy, Switzerland.

Methods. An exhaustive reassessment of the available material provides
new insights into the comparative anatomy of these turtles. The
taxonomic status of each of the 15 species typified based on material
from the Late Jurassic of the Jura Mountains is evaluated. New
diagnoses and general descriptions are provided for each valid taxon.

Results. Six out of the 15 available species names are recognized as
valid: Plesiochelys etalloni, Craspedochelys picteti, Craspedochelys
jaccardi, Tropidemys langii, Thalassemys hugii, and ‘Thalassemys’
moseri. The intraspecific variability of the shell of P. etalloni is
discussed based on a sample of about 30 relatively complete specimens
from Solothurn, Switzerland. New characters are proposed to
differentiate P. etalloni, C. picteti, and C. jaccardi, therefore
rejecting the previously proposed synonymy of these forms. Based
partly on previously undescribed specimens, the plastral morphology of
Th. hugii is redescribed. The presence of lateral plastral fontanelles
is notably revealed in this species, which calls into question the
traditional definitions of the Thalassemydidae and Eurysternidae.
Based on these new data, Eurysternum ignoratum is considered a junior
synonym of Th. hugii. The Eurysternidae are therefore only represented
by Solnhofia parsonsi in the Late Jurassic of the Jura Mountains.
Finally, ‘Th.’ moseri is recognized as a valid species, although a
referral to the genus Thalassemys is refuted.
====


A recent non-dino paper that may be of interest:

John A. Nyakatura, Emanuel Andrada, Stefan Curth & Martin S. Fischer (2014)
Bridging “Romer’s Gap”: Limb Mechanics of an Extant Belly-Dragging
Lizard Inform Debate on Tetrapod Locomotion During the Early
Carboniferous.
Evolutionary Biology (advance online publication)
DOI: 10.1007/s11692-013-9266-z
http://link.springer.com/article/10.1007%2Fs11692-013-9266-z

Free pdf:

http://www.researchgate.net/profile/John_Nyakatura/publication/259569265_Bridging_Romer's_Gap_Limb_Mechanics_of_an_Extant_Belly-Dragging_Lizard_Inform_Debate_on_Tetrapod_Locomotion_During_the_Early_Carboniferous/file/72e7e52c95d36efc10.pdf

Correction to text (free):

http://download.springer.com/static/pdf/158/art%253A10.1007%252Fs11692-014-9280-9.pdf?auth66=1399941042_091247d4e9895df183b85db35982c30d&ext=.pdf

Devonian stem tetrapods are thought to have used ‘crutching’ on land,
a belly-dragging form of synchronous forelimb action-powered
locomotion. During the Early Carboniferous, early tetrapods underwent
rapid radiation, and the terrestrial locomotion of crown-group node
tetrapods is believed to have been hindlimb-powered and ‘raised’,
involving symmetrical gaits similar to those used by modern
salamanders. The fossil record over this period of evolutionary
transition is remarkably poor (Romer’s Gap), but we hypothesize a
phase of belly-dragging sprawling locomotion combined with symmetrical
gaits. Since belly-dragging sprawling locomotion has differing
functional demands from ‘raised’ sprawling locomotion, we studied the
limb mechanics of the extant belly-dragging blue-tongued skink. We
used X-ray reconstruction of moving morphology to quantify the
three-dimensional kinematic components, and simultaneously recorded
single limb substrate reaction forces (SRF) in order to calculate SRF
moment arms and the external moments acting on the proximal limb
joints. In the hindlimbs, stylopodal long-axis rotation is more
emphasized than in the forelimbs, and much greater vertical and
propulsive forces are exerted. The SRF moment arm acting on the
shoulder is at a local minimum at the instant of peak force. The
hindlimbs display patterns that more closely resemble ‘raised’
sprawling species. External moment at the shoulder of the skink is
smaller than in ‘raised’ sprawlers. We propose an evolutionary
scenario in which the locomotor mechanics of belly-dragging early
tetrapods were gradually modified towards hindlimb-powered, raised
terrestrial locomotion with symmetrical gait. In accordance with the
view that limb evolution was an exaptation for terrestrial locomotion,
the kinematic pattern of the limbs for the generation of propulsion
preceded, in our scenario, the evolution of permanent body weight
support.