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[dinosaur] Arboreal mammal bone + ophthalmosaurid limb microanatomy + Early Mississippian tetrapod ecosystem in Scotland




Ben Creisler
bcreisler@gmail.com

Some recent non-dino papers:


Free pdf:

Fabio Alfieri, John A. Nyakatura & Eli Amson (2020)
Evolution of bone cortical compactness in slow arboreal mammals.
Evolution (advance online publication)
doi: Âhttps://doi.org/10.1111/evo.14137
https://onlinelibrary.wiley.com/doi/10.1111/evo.14137

Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1111/evo.14137

Convergent evolution is a major topic in evolutionary biology. Low bone cortical compactness (CC, a measure of porosity of cortical bone) in the extant genera of "tree sloths," has been linked to their convergent slow arboreal ecology. This proposed relationship of low CC with a slow arboreal lifestyle suggests potential convergent evolution of this trait in other slow arboreal mammals. Femoral and humeral CC were analyzed in "tree sloths," lorisids, koala, and extinct palaeopropithecids and Megaladapis, in comparison to closely related but ecologically distinct taxa, in a phylogenetic framework. Low CC in "tree sloths" is unparalleled by any analyzed clade and the high CC in extinct sloths suggests the recent convergence of low CC in "tree sloths." A tendency for low CC was found in Palaeopropithecus and Megaladapis. However, lorisids and the koala yielded unexpected CC patterns, preventing the recognition of a straightforward convergence of low CC in slow arboreal mammals. This study uncovers a complex relationship between CC and convergent evolution of slow arboreality, highlighting the multifactorial specificity of bone microstructure.

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Talevi Marianella, Campos Lisandro & S. FernÃndez Marta (2020)
Microanatomy and histology of the distal limb elements of Ophthalmosaurids from the Middle Jurassic to the Lower Cretaceous of the NeuquÃn Basin, Patagonia, Argentina.
Cretaceous Research 104737 (advance online publication)
doi: https://doi.org/10.1016/j.cretres.2020.104737
https://www.sciencedirect.com/science/article/abs/pii/S0195667120304249


Highlights

First report of distal limb elements microstructure and paleohistology in Ophthalmosaurids.
Presence of abundant cartilage in articular and non-articular surfaces of the phalanges independently of ontogenetic age and shape.
The loss of perichondral tissue is not related to the shape of the distal limb elements.


Abstract

One of the most significant morphological modifications in numerous tetrapod lineages in their secondary adaptation to life in open marine environment is the transformation of the limb into fins. The loss of perichondral bone has been pointed out as the mechanism through which this transformation was achieved. Advanced ichthyosaurs, including ophthalmosaurids, are characterized by the zeugopodium and autopodium not clearly differentiated, and bones dorsoventrally flattened and nodular. In the case of distal limb elements, particularly phalanges, two main arrangements can be recognized in dorsal and ventral views: one is characterized by spaced and quite rounded elements, whereas in the other phalanges tightly packed arrangement is observed, showing almost straight articular surfaces which result in polygonal outlines. Previously only distal limb elements of non-ophthalmosaurids, were described. In this study, we describe and interpret the microstructure of distal limb elements of six specimens of ichthyosaur, five ophthalmosaurids and one non-ophthalmosaurid. Our result shows persistence of abundant cartilage in articular and non-articular surfaces (with exception of the dorsal and ventral surfaces) independently of ontogenetic stage and shape. The coat layer of calcified cartilage is thicker in juvenile than adult specimens and this could be related to the bone remodeling. It is probable that the persistence of significant amount of cartilage in the joint surfaces of the distal limb elements of ichthyosaurs would be linked to more evenly distribute forces through the limb, the increase in the number of articulations and the increase maneuverability during swimming.

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C.E. Bennett, T.I. Kearsey, S.J. Davies, M.J. Leng, D. Millward, T.R. Smithson, P.J. Brand, M.A.E. Brown, D.K. Carpenter, J.E.A. Marshall, H. Dulson & L. Curry (2020)
Palaeoecology and palaeoenvironment of Mississippian coastal lakes and marshes during the early terrestrialisation of tetrapods.
Palaeogeography, Palaeoclimatology, Palaeoecology 110194 (advance online publication)
doi: https://doi.org/10.1016/j.palaeo.2020.110194
https://www.sciencedirect.com/science/article/abs/pii/S0031018220306428


Highlights

New terrestrial ecosystems established in the Tournaisian after a mass extinction.
Dolostones and evaporites are common in tetrapod-bearing successions of Scotland.
Dolomite formed occurred in open and closed saline lakes, brine pans and sabkhas.
The lakes were a habitat for a diverse vertebrate, mollusc and arthropod fauna.
Saline lakes may be important in the radiation of life from marine to freshwater.

Abstract

The Ballagan Formation of northern Britain provides an exceptional record of Early Mississippian ecosystems that developed as tetrapods emerged onto land. In this paper, we study two 500-metre sections of the formation near Berwick-upon-Tweed, which are characterised by abundant ferroan dolostone beds. Five lithofacies are identified: cemented siltstone and sandstone, homogeneous dolomicrite, mixed dolomite and siltstone, mixed calcite and dolomite, and dolomite with evaporite minerals. Cemented sediments have non-planar to planar subhedral dolomite crystals, up to 40âÎm in size, whereas other facies predominantly comprise dolomicrite or planar euhedral dolomite rhombs 15âÎm in size, with patches of larger rhombs indicating partial recrystallisation. The macro- and microfossil content of the dolostones is dominated by sarcopterygian (rhizodont) and actinopterygian fish, bivalves, Serpula, ostracods and Chondrites trace fossils; with rarer Spirorbis, chondrichthyans (Ageleodus, hybodonts and ?ctenacanths, xenacanths), non-gyracanth acanthodians, gastropods, eurypterids, brachiopods, plant debris, wood, lycopsid roots, charcoal, megaspores, phycosiphoniform burrows, Zoophycos? and Rhizocorallium. The oxygen and carbon isotope composition of dolomites range from â3.6â to â1.7â (for Î18O) and â2.6â to +1.6â (for Î13C) respectively indicating dolomite growth in mixed salinity waters. Frequent marine storm-surge events transported marine waters and animals into floodplain lakes, where evaporation, interstitial sulphate-reducing bacteria, iron reduction and methanogenesis allowed dolomite growth in the shallow sub-surface. Secondary pedogenic modification (by roots, brecciation, desiccation, and soil forming processes) is common and represents lake evaporation with, in some cases, saline marsh development. The dolostone facies are part of a complex environmental mosaic of sub-aerial dry floodplain, wet marshy floodplains, rivers, and lakes ranging in salinity from freshwater to hypersaline. Marine influence is strongest at the base of the formation and decreases over time, as the floodplain became drier, and forested areas became more established. Coastal lakes were an important habitat for animals recovering from the end-Devonian Hangenberg Crisis and may have acted as a pathway for euryhaline fishes, molluscs and arthropods to access freshwater environments.

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Free pdf:

Guillaume Poncelet and Sebastian M. Shimeld (2020)
The evolutionary origins of the vertebrate olfactory system.
Open Biology 10(12): 200330
doi: https://doi.org/10.1098/rsob.200330
https://royalsocietypublishing.org/doi/10.1098/rsob.200330

Free pdf:
https://royalsocietypublishing.org/doi/pdf/10.1098/rsob.200330


Vertebrates develop an olfactory system that detects odorants and pheromones through their interaction with specialized cell surface receptors on olfactory sensory neurons. During development, the olfactory system forms from the olfactory placodes, specialized areas of the anterior ectoderm that share cellular and molecular properties with placodes involved in the development of other cranial senses. The early-diverging chordate lineages amphioxus, tunicates, lampreys and hagfishes give insight into how this system evolved. Here, we review olfactory system development and cell types in these lineages alongside chemosensory receptor gene evolution, integrating these data into a description of how the vertebrate olfactory system evolved. Some olfactory system cell types predate the vertebrates, as do some of the mechanisms specifying placodes, and it is likely these two were already connected in the common ancestor of vertebrates and tunicates. In stem vertebrates, this evolved into an organ system integrating additional tissues and morphogenetic processes defining distinct olfactory and adenohypophyseal components, followed by splitting of the ancestral placode to produce the characteristic paired olfactory organs of most modern vertebrates.




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