Ben Creisler
Some recent tetrapod, bird, and mammal papers (with free pdfs) that may be of interest:
The size and shape of articular cartilage in the limbs of extant vertebrates are highly variable, yet they are critical for understanding joint and limb function in an evolutionary context. For example, inferences about unpreserved articular cartilage in early tetrapods have implications for how limb length, joint range of motion, and muscle leverage changed over the tetrapod water-land transition. Extant salamanders, which are often used as functional models for early limbed vertebrates, have much thicker articular cartilage than most vertebrate groups, but the exact proportion of cartilage and how it varies across salamander species is unknown. I aimed to quantify this variation in a sample of 13 salamanders representing a broad range of sizes, modes of life, and genera. Using contrast-enhanced micro-CT, cartilage dimensions and bone length were measured non-destructively in the humerus, radius, ulna, femur, tibia, and fibula of each specimen. Cartilage correction factors were calculated as the combined thickness of the proximal and distal cartilages divided by the length of the bony shaft. Articular cartilage added about 30% to the length of the long bones on average. Cartilage was significantly thicker in aquatic salamanders (42 Â 14% in the humerus and 35 Â 8 in the femur) than in terrestrial salamanders (21 Â 7% in both humerus and femur). There was no consistent relationship between relative cartilage thickness and body size or phylogenetic relatedness. In addition to contributing to limb length, cartilage caps increased the width and breadth of the epiphyses by amounts that varied widely across taxa. To predict the effect of salamander-like cartilage correction factors on muscle leverage, a simplified model of the hindlimb of the Devonian stem tetrapod Acanthostega was built. In this model, the lever arms of muscles that cross the hip at an oblique angle to the femur was increased by up to six centimeters. Future reconstructions of osteological range of motion and muscle leverage in stem tetrapods and stem amphibians can be made more rigorous by explicitly considering the possible effects of unpreserved cartilage and justifying assumptions based on available data from extant taxa, including aquatic and terrestrial salamanders.
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Free pdf:
Ian J. Ausprey (2021)
Adaptations to light contribute to the ecological niches and evolution of the terrestrial avifauna.
Proceedings of the Royal Society B: Biological Sciences 288(1950): 20210853
doi: Â
https://doi.org/10.1098/rspb.2021.0853https://royalsocietypublishing.org/doi/10.1098/rspb.2021.0853https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2021.0853Electronic supplementary material is available online at
https://doi.org/10.6084/m9.figshare.c.5411998.
The role of light in structuring the ecological niche remains a frontier in understanding how vertebrate communities assemble and respond to global change. For birds, eyes represent the primary external anatomical structure specifically evolved to interpret light, yet eye morphology remains understudied compared to movement and dietary traits. Here, I use Stanley Ritland's unpublished measurements of transverse eye diameter from preserved specimens to explore the ecological and phylogenetic drivers of eye morphology for a third of terrestrial avian diversity (N = 2777 species). Species with larger eyes specialized in darker understory and forested habitats, foraging manoeuvres and prey items requiring long-distance optical resolution and were more likely to occur in tropical latitudes. When compared to dietary and movement traits, eye size was a top predictor for habitat, foraging manoeuvre, diet and latitude, adding 8â28% more explanatory power. Eye size was phylogenetically conserved (Î = 0.90), with phylogeny explaining 61% of eye size variation. I suggest that light has contributed to the evolution and assembly of global vertebrate communities and that eye size provides a useful predictor to assess community response to global change.
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Free pdf:
Anton F.-J. Wroblewski & Bonnie E. Gulas-Wroblewski (2021)
Earliest evidence of marine habitat use by mammals.
Scientific Reports 11, Article number: 8846
doi:
https://doi.org/10.1038/s41598-021-88412-3https://www.nature.com/articles/s41598-021-88412-3Free pdf:
https://www.nature.com/articles/s41598-021-88412-3.pdfEvidence for the earliest invasion of the marine realm by mammals was previously restricted to Eocene (48.6â37.8 Ma) skeletal remains. We report incontrovertible ichnofossil evidence for brackish-water habitat use by at least two mammalian species in southern Wyoming during the late Paleocene (58 Ma). These are the first Paleocene mammal trackways recorded in the United States and only the fourth documented in the world. Multiple tracks preserved in restricted marine deposits represent animals repeatedly walking across submerged to partially emergent tidal flats. Hundreds of tracks are preserved in planform and cross-sectional exposure within five horizons along a 1032 m tracksite. Four prints exhibit five clear toe imprints, while two others distinctly display four toes. Some tracks penetrate beds populated by dwelling traces of marine bivalves and polychaetes in the upper layers and sea anemones at the base. Candidates for the five-toed tracemakers are pantodonts such as Titanoides, Barylambda, and Coryphodon, which have been recovered from late Paleocene strata throughout western North America. The four-toed tracks provide the earliest evidence of previously-undescribed large artiodactyls and/or tapiroids, mutually supporting recent molecular phylogenetic studies that place the origin of Cetartiodactyla near the Cretaceous-Paleogene boundary (~â67.7 Ma). Collectively, these trackways irrefutably demonstrate the utility of ichnological data in reconstructing the evolutionary history and adaptive behaviors of extinct taxa beyond the evidence provided by body fossils alone.
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Free pdf:
Marina Melchionna, Antonio Profico, Silvia Castiglione, Carmela Serio, Alessandro Mondanaro, Maria Modafferi, Davide Tamagnini, Luigi Maiorano, Pasquale Raia, Lawrence M. Witmer, Stephen Wroe & Gabriele Sansalone (2021)
A method for mapping morphological convergence on threeâdimensional digital models: the case of the mammalian sabreâtooth.
Palaeontology (advance online publication)
doi:
https://doi.org/10.1111/pala.12542 https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12542Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1111/pala.12542Morphological convergence can be assessed using a variety of statistical methods. None of the methods proposed to date enable the visualization of convergence. All are based on the assumption that the phenotypes either converge, or do not. However, between species, morphologically similar regions of a larger structure may behave differently. Previous approaches do not identify these regions within the larger structures or quantify the degree to which they may contribute to overall convergence. Here, we introduce a new method to chart patterns of convergence on threeâdimensional models using the R function conv.map. The convergence between pairs of models is mapped onto them to visualize and quantify the morphological convergence. We applied conv.map to a wellâknown case study, the sabreâtooth morphotype, which has evolved independently among distinct mammalian clades from placentals to metatherians. Although previous authors have concluded that sabreâtooths kill using a stabbing âbiteâ to the neck, others have presented different interpretations for specific taxa, including the iconic Smilodon and Thylacosmilus. Our objective was to identify any shared morphological features among the sabreâtooths that may underpin similar killing behaviours. From a sample of 49 placental and metatherian carnivores, we found stronger convergence among sabreâtooths than for any other taxa. The morphological convergence is most apparent in the rostral and posterior parts of the cranium. The extent of this convergence suggests similarity in function among these phylogenetically distant species. In our view, this function is most likely to be the killing of relatively large prey using a stabbing bite.
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