[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Mesozoic non-dino papers: marine reptiles, turtles, labyrinthodonts
From: Ben Creisler
A number of new non-dino papers that may be of interest:
Neil P. Kelley, Ryosuke Motani, Da-yong Jiang, Olivier Rieppel & Lars
Selective extinction of Triassic marine reptiles during long-term
sea-level changes illuminated by seawater strontium isotopes.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
The relationship between cycles of sea-level change and marine
diversity has long been the subject of debate. Large predators may be
particularly sensitive to changes in habitat availability and marine
productivity driven by changes in sea-level, especially those
dependent on nearshore benthic food resources. To test this
relationship, we compared the proportional diversity of differing
marine reptile ecotypes through the Triassic with the isotopic
composition of seawater strontium (87Sr/ 86Sr), a geochemical index
linked to tectonically controlled sea-level change. The proportional
abundance of marine reptiles adapted toward a diet of shelled prey
rose during times of rapid sea-level rise and fell during times of
rapid sea-level fall, while open water forms were more resistant to
these changes. Our results indicate that the rate of sea-level change,
rather than the absolute magnitude of sea-level or flooded shelf area,
played a role in shaping patterns of ecological diversification and
ecologically selective extinction during the Triassic. The link
between the isotopic composition of seawater strontium and the
evolution of marine reptiles demonstrates that sea-level change played
an important role in the structuring of marine ecosystems over
José Patricio O'Gorman, Leonardo Salgado, Ignacio Alejandro Cerda &
Zulma Gasparini (2012)
First record of gastroliths associated with elasmosaur remains from La
Colonia Formation (Campanian-Maastrichtian), Chubut, Patagonia
Argentina, with comments on the probable depositional
palaeoenvironment of the source of the gastroliths.
Cretaceous Research (advance online publication)
A gastrolith set, comprising 197 elements, associated with an
indeterminate elasmosaurid plesiosaur collected from the
Campanian-Maastrichtian La Colonia Formation, Chubut, Argentina, is
described. Most of the gastroliths are discoidal (41.9%) or spheroidal
(34.8%), with a mean Maximum Projection Sphericity Index value of 0.69
and a mean OP Index value of -0.74. The values of these indices are
compared with those recorded for gastroliths associated with other
Upper Cretaceous elasmosaurids to see if patterns with
palaeobiological relevance are evident. The mean values of the Maximum
Projection Sphericity Index and the Oblate-Prolate Index allow us to
infer a fluvial or estuarine origin for all the elasmosaurid
gastroliths for which these indices have been calculated. This
inference is palaeobiologically informative because it indicates that
at least some Upper Cretaceous elasmosaurs entered into estuarine (or
fluvial) environments. It also helps explain the interesting
vertebrate assemblage of the Allen and La Colonia formations where a
rich continental fauna is recorded but elasmosaurids and polycotylids
are the only well represented vertebrates with marine affinities.
Ingmar Werneburg (2012)
Jaw musculature during the dawn of turtle evolution.
Organisms Diversity & Evolution (advance online publication)
Using a new approach to study muscle anatomy in vertebrates, the fully
differentiated jaw musculature of 42 turtle species was studied and
character mappings were performed. Soft tissue arrangements were
correlated to the temporal openings (emarginations) of the skull and
the trochlearis system of the jaw apparatus among turtle taxa. When
compared to the cranial anatomy of stem Testudines, most characters
detected as diagnostic of particular extant groups have to be
considered as being evolved first within Testudines. Hence, jaw muscle
anatomy of extant turtles is difficult to compare to that of other
reptilian taxa. Moreover, the high number of apomorphic character
changes speaks for a divergating turtle and saurian morphotype of jaw
musculature, which could indicate either a position of turtles outside
of Sauria or a highly derived, undetectable origin within that group.
In general, a low direct correlation of most soft and hard tissue
characters was detected. This finding could imply that both character
complexes are more integrated to each other driven by functional
morphology; i.e., the composition of muscle fibre types. That
condition highlights the difficulty in using gross anatomy of jaw
muscle characters to interpret temporal bone arrangements among
amniotes in general.
Ylenia Chiari, Vincent Cahais, Nicolas Galtier and Frederic Delsuc (2012)
Phylogenomic analyses support the position of turtles as the sister
group of birds and crocodiles (Archosauria).
BMC Biology 2012, 10:65 (provisional version)
NOTE: pdf is Open Access
The morphological peculiarities of turtles have, for a long time,
impeded their accurate placement in the phylogeny of amniotes.
Molecular data used to address this major evolutionary question have
so far been limited to a handful of markers and/or taxa. These studies
have supported conflicting topologies, positioning turtles as either
the sister group to all other reptiles, to lepidosaurs (tuatara,
lizards and snakes), to archosaurs (birds and crocodiles), or to
crocodilians. Genome-scale data have been shown to be useful in
resolving other debated phylogenies, but no such adequate dataset is
yet available for amniotes.
In this study, we used next-generation sequencing to obtain seven new
transcriptomes from the blood, liver, or jaws from four turtles, a
caiman, a lizard, and a lungfish. We used a phylogenomic dataset based
on 248 nuclear genes (187,026 nucleotide sites) for 16 vertebrate taxa
to resolve the origins of turtles. Maximum likelihood and Bayesian
concatenation analyses and species tree approaches performed under the
most realistic models of the nucleotide and amino acid substitution
processes unambiguously support turtles as a sister group to birds and
crocodiles. The use of more simplistic models of nucleotide
substitution for both concatenation and species tree reconstruction
methods leads to the artefactual grouping of turtles and crocodiles,
most likely because of substitution saturation at third codon
positions. Relaxed molecular clock methods estimate the divergence
between turtles and archosaurs around 255 million years ago. The most
recent common ancestor of living turtles, corresponding to the split
between Pleurodira and Cryptodira, is estimated to have occurred
around 157 million years ago, in the Upper Jurassic period. This is a
more recent estimate than previously reported, and questions the
interpretation of controversial Lower Jurassic fossils as being part
of the extant turtles radiation.
These results provide a phylogenetic framework and timescale with
which to interpret the evolution of the peculiar morphological,
developmental, and molecular features of turtles within the amniotes.
S. Blair Hedges (2012)
Amniote phylogeny and the position of turtles.
BMC Biology 1 (64)
NOTE: pdf is Open Access
The position of turtles among amniotes remains in dispute, with
morphological and molecular comparisons giving different results.
Morphological analyses align turtles with either lizards and their
relatives, or at the base of the reptile tree, whereas molecular
analyses, including a recent study by Chiari et al. in BMC Biology,
place turtles with birds and crocodilians. Molecular studies have not
wavered as the numbers of genes and species have increased, but
morphologists have been reluctant to embrace the molecular tree.
Edwin A. Cadena & Mary H. Schweitzer (2012)
Variation in osteocytes morphology vs bone type in turtle shell and
their exceptional preservation from the Jurassic to the present.
Bone 51(3): 614-620
Here we describe variations in osteocytes derived from each of the
three bone layers that comprise the turtle shell. We examine
osteocytes in bone from four extant turtle species to form a
morphological 'baseline', and then compare these with morphologies of
osteocytes preserved in Cenozoic and Mesozoic fossils. Two different
morphotypes of osteocytes are recognized: flattened-oblate osteocytes
(FO osteocytes), which are particularly abundant in the internal
cortex and lamellae of secondary osteons in cancellous bone, and
stellate osteocytes (SO osteocytes), principally present in the
interstitial lamellae between secondary osteons and external cortex.
We show that the morphology of osteocytes in each of the three bone
layers is conserved through ontogeny. We also demonstrate that these
morphological variations are phylogenetically independent, as well as
independent of the bone origin (intramembranous or endochondral).
Preservation of microstructures consistent with osteocytes in the
morphology in Cenozoic and Mesozoic fossil turtle bones appears to be
common, and occurs in diverse diagenetic environments including
marine, freshwater, and terrestrial deposits. These data have
potential to illuminate aspects of turtle biology and evolution
previously unapproachable, such as estimates of genome size of extinct
species, differences in metabolic rates among different bones from a
single individual, and potential function of osteocytes as capsules
for preservation of ancient biomolecules.
I. V. Novikov (2012)
New data on trematosauroid labyrinthodonts of Eastern Europe: 4. Genus
Benthosuchus Efremov, 1937.
Paleontological Journal 46(4): 400-411
The trematosauroid genus Benthosuchus Efremov, 1937 is revised and its
diagnosis is emended. This genus includes the previously established
B. sushkini, B. korobkovi, and B. bashkiricus, and the new species B.
gusevae described here. The new form is archaic relative to congeners
and is similar in a number of characters to the archaic capitosaurid
Wetlugasaurus samarensis, which confirms direct affinity of the two