Ben Creisler
New avian-related papers:
Amanda R. Falk, James C. Lamsdell and Enpu Gong (2020)
Principal component analysis of avian hind limb and foot morphometrics and the relationship between ecology and phylogeny.
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2020.39
https://www.cambridge.org/core/journals/paleobiology/article/principal-component-analysis-of-avian-hind-limb-and-foot-morphometrics-and-the-relationship-between-ecology-and-phylogeny/144C8D8E6E3ECD3A119A3AE7A5401FC2
Principal component analysis of avian hind limb and foot morphometrics and the relationship between ecology and phylogeny.
Paleobiology (advance online publication)
DOI: https://doi.org/10.1017/pab.2020.39
https://www.cambridge.org/core/journals/paleobiology/article/principal-component-analysis-of-avian-hind-limb-and-foot-morphometrics-and-the-relationship-between-ecology-and-phylogeny/144C8D8E6E3ECD3A119A3AE7A5401FC2
Principal component analysis has been used to test for similarities in ecology and life habit between modern and fossil birds; however, the two main portions of the hind limb--the foot and the long bone elements--have not been examined separately. We examine the potential links between morphology, ecology, and phylogeny through a synthesis of phylogenetic paleoecological methods and morphospace analysis. Both hind limb morphologies and speciesâ ecologies exhibit extreme phylogenetic clumping, although these patterns are at least partially explainable by a Brownian motion style of evolution. Some morphologies are strongly correlated with particular ecologies, while some ecologies are occupied by a variety of morphologies. Within the morphospace analyses, the length of the hallux (toe I) is the most defining characteristic of the entire hind limb. The foot and hind limb are represented on different axes when all measurements are considered in an analysis, suggesting that these structures undergo morphological change separately from each other. Early birds tend to cluster together, representing an unspecialized basal foot morphotype and a hind limb reliant on hip-driven, not knee-driven, locomotion. Direct links between morphology, ecology, and phylogeny are unclear and complicated and may be biased due to sample size (~60 species). This study should be treated as a preliminary analysis that further studies, especially those examining the vast diversity of modern birds, can build upon.
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Daniel G. Blackburn (2020)
Functional morphology, diversity, and evolution of yolk processing specializations in embryonic reptiles and birds.
Journal of Morphology (advance online publication)
doi: https://doi.org/10.1002/jmor.21267
https://onlinelibrary.wiley.com/doi/10.1002/jmor.21267
Evolution of the terrestrial, amniotic egg of vertebrates required new mechanisms by which yolk material could be processed for embryonic use. Recent studies on each of the major extant reptile groups have revealed elaborate morphological specializations for yolk processing, features that differ dramatically from those of birds. In the avian pattern, liquid yolk is housed in a yolk sac whose endodermal lining absorbs and digests yolk material and sends resultant nutrients into the blood circulation. In snakes, lizards, turtles, and crocodilians, as documented herein, the yolk sac becomes invaded by endodermal cells that proliferate and phagocytose yolk material. Blood vessels then invade, and the endodermal cells become arranged around them, forming elongated "spaghettiâlike" strands that fill the yolk sac cavity. This pattern provides an effective means by which yolk material is cellularized, digested, and transported by vitelline vessels to the developing embryo. Phylogenetically, the (nonâavian) "reptilian" pattern was ancestral for sauropsids and was modified or replaced in ancestors to birds. This review postulates that evolution of the "avian" pattern involved increased reliance on extracellular digestion of yolk, allowing embryonic development to occur more rapidly than in typical reptiles. Comparative studies of yolk processing that draw on morphological, biochemical, molecular approaches are needed to explain how and why the "reptilian" pattern was replaced in birds or their archosaurian ancestors.
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