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New Jurassic Portlandemys species + microsaurs + early amphibians + varanoid lizards



Ben Creisler
bcreisler@gmail.com


New papers in PLoS ONE that may be of interest:


Jérémy Anquetin , Christian Püntener & Jean-Paul Billon-Bruyat (2015)
Portlandemys gracilis n. sp., a New Coastal Marine Turtle from the
Late Jurassic of Porrentruy (Switzerland) and a Reconsideration of
Plesiochelyid Cranial Anatomy.
PLoS ONE 10(6): e0129193.
doi:10.1371/journal.pone.0129193
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0129193


Background

Several groups of stem cryptodires became adapted to coastal marine
environments as early as the Late Jurassic, 40 million years before
the Pan-Chelonioidea. The Plesiochelyidae are a major component of
this first radiation of crown-group turtles into marine habitats. They
are abundant in many European localities, but their systematics is
still greatly confused. Only three species are represented by cranial
material: Plesiochelys etalloni, Plesiochelys planiceps, and
Portlandemys mcdowelli.

Methodology/Principal Findings

In the present study, we describe a cranium and a mandible from the
Kimmeridgian of Porrentruy (Switzerland), which we refer to a new
species, Portlandemys gracilis n. sp. This new taxon differs from
Portlandemys mcdowelli in several aspects of the cranium and mandible,
notably in being generally more gracile, but the two species share a
narrow skull, a more acute angle between the labial ridges on the
mandible, and a unique configuration of the anterodorsal part of the
basicranium. The cranial anatomy of plesiochelyid turtles is discussed
in details based primarily on these new specimens and new cranial
material of Plesiochelys etalloni from Solothurn, Switzerland.

Conclusions/Significance

Several characters (e.g., the contribution of the parietal to the
foramen nervi trigemini, the configuration of the dorsum sellae and
sella turcica, the presence of an infolding ridge on the posterior
surface of the quadrate) appear as potential candidates to help
elucidate plesiochelyid relationships. Some of these characters are
included in a previously published phylogenetic dataset and help to
stabilize the relationships of plesiochelyid turtles and closely
related taxa. For the first time, our results suggest that
plesiochelyids, 'Thalassemys' moseri, and Solnhofia parsonsi
(representing the Eurysternidae) form a clade at the base of
Eucryptodira.
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Jason D. Pardo , Matt Szostakiwskyj & Jason S. Anderson (2015)
Cranial Morphology of the Brachystelechid ‘Microsaur’ Quasicaecilia
texana Carroll Provides New Insights into the Diversity and Evolution
of Braincase Morphology in Recumbirostran ‘Microsaurs’.
PLoS ONE 10(6): e0130359.
doi:10.1371/journal.pone.0130359
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0130359

Recumbirostran ‘microsaurs,’ a group of early tetrapods from the Late
Carboniferous and Early Permian, are the earliest known example of
adaptation to head-first burrowing in the tetrapod fossil record.
However, understanding of the diversity of fossorial adaptation within
the Recumbirostra has been hindered by poor anatomical knowledge of
the more divergent forms within the group. Here we report the results
of μCT study of Quasicaecilia texana, a poorly-known recumbirostran
with a unique, broad, shovel-like snout. The organization of the skull
roof and braincase of Quasicaecilia is found to be more in line with
that of other recumbirostrans than previously described, despite
differences in overall shape. The braincase is found to be broadly
comparable to Carrolla craddocki, with a large presphenoid that
encompasses much of the interorbital septum and the columella
ethmoidalis, and a single compound ossification encompassing the
sphenoid, otic, and occipital regions. The recumbirostran braincase
conserves general structure and topology of braincase regions and
cranial nerve foramina, but it is highly variable in the number of
ossifications and their extent, likely associated with the reliance on
braincase ossifications to resist compression during sediment
compaction and mechanical manipulation by epaxial and hypaxial
musculature. Expansion of the deep ventral neck musculature in
Quasicaecilia, autapomorphic among recumbirostrans, may reflect unique
biomechanical function, and underscores the importance of future
attention to the role of the cervical musculature in contextualizing
the origin and evolution of fossoriality in recumbirostrans.



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Jordi Marcé-Nogué, Josep Fortuny, Soledad De Esteban-Trivigno,
Montserrat Sánchez, Lluís Gil & Àngel Galobart  (2015)
3D Computational Mechanics Elucidate the Evolutionary Implications of
Orbit Position and Size Diversity of Early Amphibians.
PLoS ONE 10(6): e0131320.
doi:10.1371/journal.pone.0131320
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0131320



For the first time in vertebrate palaeontology, the potential of
joining Finite Element Analysis (FEA) and Parametrical Analysis (PA)
is used to shed new light on two different cranial parameters from the
orbits to evaluate their biomechanical role and evolutionary patterns.
The early tetrapod group of Stereospondyls, one of the largest groups
of Temnospondyls is used as a case study because its orbits position
and size vary hugely within the members of this group. An adult skull
of Edingerella madagascariensis was analysed using two different cases
of boundary and loading conditions in order to quantify stress and
deformation response under a bilateral bite and during skull raising.
Firstly, the variation of the original geometry of its orbits was
introduced in the models producing new FEA results, allowing the
exploration of the ecomorphology, feeding strategy and evolutionary
patterns of these top predators. Secondly, the quantitative results
were analysed in order to check if the orbit size and position were
correlated with different stress patterns. These results revealed that
in most of the cases the stress distribution is not affected by
changes in the size and position of the orbit. This finding supports
the high mechanical plasticity of this group during the Triassic
period. The absence of mechanical constraints regarding the orbit
probably promoted the ecomorphological diversity acknowledged for this
group, as well as its ecological niche differentiation in the
terrestrial Triassic ecosystems in clades as lydekkerinids,
trematosaurs, capitosaurs or metoposaurs.


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Matthew R. McCurry, Michael Mahony, Phillip D. Clausen, Michelle R.
Quayle, Christopher W. Walmsley, Tim S. Jessop, Stephen Wroe, Heather
Richards & Colin R. McHenry(2015)
The Relationship between Cranial Structure, Biomechanical Performance
and Ecological Diversity in Varanoid Lizards.
PLoS ONE 10(6): e0130625.
doi:10.1371/journal.pone.0130625
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0130625

Skull structure is intimately associated with feeding ability in
vertebrates, both in terms of specific performance measures and
general ecological characteristics. This study quantitatively assessed
variation in the shape of the cranium and mandible in varanoid
lizards, and its relationship to structural performance (von Mises
strain) and interspecific differences in feeding ecology. Geometric
morphometric and linear morphometric analyses were used to evaluate
morphological differences, and finite element analysis was used to
quantify variation in structural performance (strain during simulated
biting, shaking and pulling). This data was then integrated with
ecological classes compiled from relevant scientific literature on
each species in order to establish structure-function relationships.
Finite element modelling results showed that variation in cranial
morphology resulted in large differences in the magnitudes and
locations of strain in biting, shaking and pulling load cases. Gracile
species such as Varanus salvadorii displayed high strain levels during
shaking, especially in the areas between the orbits. All models
exhibit less strain during pull back loading compared to shake
loading, even though a larger force was applied (pull =30N, shake =
20N). Relationships were identified between the morphology,
performance, and ecology. Species that did not feed on hard prey
clustered in the gracile region of cranial morphospace and exhibited
significantly higher levels of strain during biting (P = 0.0106).
Species that fed on large prey clustered in the elongate area of
mandible morphospace. This relationship differs from those that have
been identified in other taxonomic groups such as crocodiles and
mammals. This difference may be due to a combination of the open
‘space-frame’ structure of the varanoid lizard skull, and the ‘pull
back’ behaviour that some species use for processing large prey.