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[dinosaur] Gansus foot scales + iridescent feather evolution + birds of Gondwana Rainforests (free pdfs)




Ben Creisler
bcreisler@gmail.com

Some recent avian-related papers:


Free pdf:

Tao Zhao, Zhiheng LI, He Zhang & Yanhong Pan (2021)
Foot scales in the Early Cretaceous bird Gansus yumenensis from China.
bioRxiv 2021.06.07.447457 (preprint)
doi: https://doi.org/10.1101/2021.06.07.447457
https://www.biorxiv.org/content/10.1101/2021.06.07.447457v1


Most modern birds have scales covering the foot and feathers elsewhere. Discoveries of fossil feathers attached to the metatarsus in non-avian dinosaurs and basal birds suggests that the avian scales are secondarily derived from feathers. However, our knowledge of early avian scales and their taphonomy is still limited, due to the scarcity of fossil record. Here we employ multiple techniques to characterize the morphological and chemical details preserved and investigate how they are preserved in the skin of IVPP V15077, a referred specimen of the Early Cretaceous Gansus yumenensis. Results show that two types of scales, scutellate and interstitial scales, are preserved in IVPP V15077, which, in combination with previous discovery of scutate and reticulate scales in other Early Cretaceous birds, indicates that all four types of scales present in modern birds have appeared in the Early Cretaceous. SEM observations and Raman analysis suggest that the skin of Gansus yumenensis may be pigmented. Elemental mapping indicates that aluminosilicates and calcium phosphate are involved in the mineralization of the skin.

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Free pdf:

Klara K. NordÃn, Chad M. Eliason & Mary Caswell Stoddard (2021)
Evolution of brilliant iridescent feather nanostructures.
bioRxiv 2021.05.31.446390 (preprint)
doi: https://doi.org/10.1101/2021.05.31.446390
https://www.biorxiv.org/content/10.1101/2021.05.31.446390v1


The brilliant iridescent plumage of birds creates some of the most stunning color displays known in the natural world. Iridescent plumage colors are produced by nanostructures in feathers and have evolved in a wide variety of birds. The building blocks of these structures--melanosomes (melanin-filled organelles)--come in a variety of forms, yet how these different forms contribute to color production across birds remains unclear. Here, we leverage evolutionary analyses, optical simulations and reflectance spectrophotometry to uncover general principles that govern the production of brilliant iridescence. We find that a key feature that unites all melanosome forms in brilliant iridescent structures is thin melanin layers. Birds have achieved this in multiple ways: by decreasing the size of the melanosome directly, by hollowing out the interior, or by flattening the melanosome into a platelet. The evolution of thin melanin layers unlocks color-producing possibilities, more than doubling the range of colors that can be produced with a thick melanin layer and simultaneously increasing brightness. We discuss the implications of these findings for the evolution of iridescent structures in birds and propose two evolutionary paths to brilliant iridescence.

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Free pdf:

Kieren J Mitchell, Andrew F Hugall, Holly Heiniger, Leo Joseph & Paul M Oliver (2021)
Disparate origins for endemic bird taxa from the 'Gondwana Rainforests' of Central Eastern Australia.
Biological Journal of the Linnean Society, blab031
doi: https://doi.org/10.1093/biolinnean/blab031
https://academic.oup.com/biolinnean/advance-article/doi/10.1093/biolinnean/blab031/6291935



Subtropical and temperate rainforests of Central Eastern Australia are some of the largest remaining fragments of their kind globally. The biota of these rainforests appears to comprise two broad biogeographical elements: a more ancient (Miocene or older) and typically upland temperate ('Gondwanan') element and a younger (Plio-Pleistocene) lowland tropical element. We present the first phylogenetic synthesis of the spatiotemporal origins for the eight bird taxa endemic to Central Eastern Australian Rainforests. At least five of these eight focal taxa show Plio-Pleistocene divergences from their respective northern sister taxa, consistent with origins driven by recent expansion and contraction of lowland rainforest. In contrast, two more strictly upland species, the rufous scrub-bird (Atrichornis rufescens) and the logrunner (Orthonyx temminckii), diverged from their nearest living relatives during the Miocene, suggesting potentially longer histories of persistence and more temperate origins. Finally, we did not recover reciprocal monophyly in mitogenomes from the two extant lyrebirds, Albertâs lyrebird (Menura alberti) and the superb lyrebird (Menura novaehollandiae). The disparate divergence ages recovered among all eight taxa are consistent with the biota of the Central Eastern Australian Rainforests comprising isolates either of younger age and tropical lowland origins or of older age and temperate upland origins.



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