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[dinosaur] Metoposaurus growth + Permian-Triassic boundary in Catalan Pyrenees + limbless squamates





Ben Creisler
bcreisler@gmail.com


Some recent non-dino papers that may be of interest:


Free pdf:

Elżbieta M. Teschner, P. Martin Sander & Dorota Konietzko-Meier (2017)
Variability of growth pattern observed in Metoposaurus krasiejowensis humeri and its biological meaning.
Journal of Iberian Geology (advance online publication)
DOI: https://doi.org/10.1007/s41513-017-0038-y
https://link.springer.com/article/10.1007/s41513-017-0038-y


Free pdf:
https://link.springer.com/content/pdf/10.1007%2Fs41513-017-0038-y.pdf



Purpose

Histological studies on temnospondyl amphibian bones remain rare. A systematic revision of the histology was applied for the purpose of testing the histovariability in the humeri and becoming new information about the growth pattern.

Methods

The present study includes 12 humeri of Metoposaurus krasiejowensis, which originate from the Late Triassic clay pit near Krasiejów, southwestern Poland. The specimens were scanned with a microCT and the histological thin-sections have been obtained with the standard petrographic method.

Results

The evaluation of the studied bones shows a uniform growth series resulting in one morphotype. Strikingly, the histological analysis reveals a greater diversity with two different histotypes: Histotype I shows a distinct differentiation between alternating zones and annuli with poor to moderate vascularization and increase of bone remodeling during growth. Histotype II does not show any distinct zones and annuli but is characterized by a high vascularization and fast growth coexisting with an extensive bone remodeling.

Conclusions

Based on these two different growth patterns, several hypotheses can be established: The specimens do not show any pattern of histological variation; humeri represent a taxonomic diversity; the analyzed Metoposaurus bones stem from two different populations separated by space and; or time or sexual dimorphism.

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Eudald Mujal, Josep Fortuny, Jordi Pérez-Cano, Jaume Dinarès-Turell, Jordi Ibáñez-Insa, Oriol Oms, Isabel Vila, Arnau Bolet & Pere Anadón (2017)
Integrated multi-stratigraphic study of the Coll de Terrers late Permian–Early Triassic continental succession from the Catalan Pyrenees (NE Iberian Peninsula): A geologic reference record for equatorial Pangaea.
Global and Planetary Change (advance online publication)
doi: https://doi.org/10.1016/j.gloplacha.2017.10.004
http://www.sciencedirect.com/science/article/pii/S0921818116305756


The most severe biotic crisis on Earth history occurred during the Permian–Triassic (PT) transition around 252 Ma. Whereas in the marine realm such extinction event is well-constrained, in terrestrial settings it is still poorly known, mainly due to the lack of suitable complete sections. This is utterly the case along the Western Tethys region, located at Pangaea's equator, where terrestrial successions are typically build-up of red beds often characterised by a significant erosive gap at the base of the Triassic strata. Henceforth, documenting potentially complete terrestrial successions along the PT transition becomes fundamental. Here, we document the exceptional Coll de Terrers area from the Catalan Pyrenees (NE Iberian Peninsula), for which a multidisciplinary research is conducted along the PT transition. The red-bed succession, located in a long E-W extended narrow rift system known as Pyrenean Basin, resulted from a continuous sedimentary deposition evolving from meandering (lower Upper Red Unit) to playa-lake/ephemeral lacustrine (upper Upper Red Unit) and again to meandering settings (Buntsandstein facies). Sedimentary continuity is suggested by preliminary cyclostratigraphic analysis that warrants further analysis. Our combined sedimentological, mineralogical and geochemical data infer a humid-semiarid-humid climatic trend across the studied succession. The uppermost Permian strata, deposited under an orbitally controlled monsoonal regime, yields a relatively diverse ichnoassemblage mainly composed of tetrapod footprints and arthropod trace fossils. Such fossils indicate appropriate life conditions and water presence in levels that also display desiccation structures. These levels alternate with barren intervals formed under dry conditions, being thus indicative of strong seasonality. All these features are correlated with those reported elsewhere in Gondwana and Laurasia, and suggest that the Permian–Triassic boundary might be recorded somewhere around the Buntsandstein base. Consequently, Coll de Terrers and the whole Catalan Pyrenees become key regions to investigate in detail the Permian extinction event and the Triassic ecosystems recovery.


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Carlos R. Infante, Ashley M. Rasys & Douglas B. Menke (2017)
Appendages and gene regulatory networks: Lessons from the limbless.
Genesis (advance online publication)
DOI: 10.1002/dvg.23078  
http://onlinelibrary.wiley.com/doi/10.1002/dvg.23078/full  



Among squamate reptiles, dozens of lineages have independently evolved complete or partial limb reduction. This remarkable convergence of limbless and limb-reduced phenotypes provides multiple natural replicates of different ages to explore the evolution and development of the vertebrate limb and the gene regulatory network that controls its formation. The most successful and best known of the limb-reduced squamates are snakes, which evolved a limb-reduced body form more than 100 million years ago. Recent studies have revealed the unexpected finding that many ancient limb enhancers are conserved in the genomes of snakes. Analyses in limbed animals show that many of these limb enhancers are also active during development of the phallus, suggesting that these enhancers may have been retained in snakes due their importance in regulating transcription in the external genitalia. This hypothesis is substantiated by functional tests of snake enhancers, which demonstrate that snake enhancer elements have lost limb function while retaining genital enhancer function. The large degree of overlap in the gene regulatory networks deployed during limb and phallus development may act to constrain the divergence of shared gene network components and the evolution of appendage morphology. Future studies will reveal whether limb regulatory elements have undergone similar functional changes in other lineages of limb-reduced squamates.


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