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[dinosaur] Fossil down feather + avian squamosal + bird brain size and lifespan + more

Ben Creisler

Some recent avian-related papers:

Free pdf:

Arindam Roy, Case V. Miller, Michael Pittman, Thomas G. Kaye & Adolf Peretti (2020)
Three-dimensionally 'Stage IIIb' fossil down feather supports developmental modularity in feather evolution.
bioRxiv 2020.08.26.268060 (preprint)
doi: https://doi.org/10.1101/2020.08.26.268060

We describe a unique three-dimensionally preserved fossil down feather from the Late Cretaceous of Myanmar. The morphology is highly congruent with Stage IIIb of the widely accepted Prum and Brush model of feather evolution-development. This makes the new specimen the first evidence of this developmental stage in the fossil record. The Stage IIIb diagnosis is robustly supported by the absence of a central rachis and by its paired barbules emanating from radially positioned barbs that are attached to a short calamus. Prum and Brush model hypothesises a bifurcation in the evolution-development pathway at Stage III. Stage IIIa involves rachis development and branching into barbs. Stage IIIb involves branching of the barbs from the calamus and then further branching of the barbules from the barbs. These two pathways then converge into Stage IIIa+b where feathers produce a rachis, barbs and barbules in nested order, finally leading to Stage IV. Evolution-development studies on the morphogenesis of feathers have unequivocally shown that such feather branching can be controlled by BMP, Noggin, Shh and several other proteins. Therefore, molecular crosstalk can convert a barb into a rachis and vice versa. The topology of this down feather, consistent with specific patterns of modular protein-protein signalling already observed, provides the first definitive evidence that such signalling was responsible for the evolution of a diverse inventory of feather morphologies in non-avialan dinosaurs and early birds since the middle Jurassic.


Gerald Mayr & Albrecht Manegold (2020)
On the comparative morphology of the juvenile avian skull: an assessment of squamosal shape across avian higherâlevel taxa.
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.24504

The comparative morphology of juvenile avian skulls is poorly known. Here, we survey the shape of the squamosal (os squamosum) across juvenile skulls of avian higherâlevel clades. In all palaeognathous birds, the rostral end of the squamosal does not surpass the parietal and does not reach the frontal. This morphology is likely to be plesiomorphic for neornithine birds. A short squamosal also occurs in some Neognathae, but in most neognathous birds the squamosal contacts the frontal, and in some taxa the bone is strongly elongated and distinctly surpasses the parietal. Some clades show a notable variation in squamosal morphology. This is, for example, true for Strigiformes, where the taxon Athene differs from the other examined owls in squamosal size, and for the Passeriformes, where Old World Suboscines are characterized by a distinctive squamosal morphology. A unique derived squamosal morphology is for the first time reported for the Apodidae and Hemiprocnidae, in which the bone forms an elongated rostral process that runs along most of the orbital rim. In nonâavian theropods, the squamosal articulates with the postorbital and delimits the upper temporal opening. Extant birds lack a postorbital, but a topological correlation between the squamosal and the postorbital process is maintained in most taxa of the Neognathae. The phylogenetic significance of squamosal morphology is diminished by the fact that closely related taxa often show very disparate shapes of the bone, and squamosal morphology appears to be determined by multiple functional constraints including skull geometry, brain morphology and, possibly, nostril type.


Dante JimÃnezâOrtega, Niclas Kolm, Simone Immler, Alexei A. Maklakov & Alejandro GonzalezâVoyer (2020)
Long life evolves in large brained bird lineages.
Evolution (advance online publication)
doi: https://doi.org/10.1111/evo.14087

The brain is an energetically costly organ that consumes a disproportionate amount of resources. Species with larger brains relative to their body size have slower life histories, with reduced output per reproductive event and delayed development times that can be offset by increasing behavioral flexibility. The "cognitive buffer" hypothesis maintains that large brain size decreases extrinsic mortality due to greater behavioral flexibility, leading to a longer lifespan. Alternatively, slow life histories, and long lifespan can be a preâadaptation for the evolution of larger brains. Here we use phylogenetic path analysis to contrast different evolutionary scenarios and disentangle direct and indirect relationships between brain size, body size, life history and longevity across 339 altricial and precocial bird species. Our results support both a direct causal link between brain size and lifespan, and an indirect effect via other life history traits. These results indicate that large brain size engenders longer life, as proposed by the "cognitive buffer" hypothesis.


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Ivan J. Starikov and Michael Wink (2020)
Old and Cosmopolite: Molecular Phylogeny of TropicalâSubtropical Kites (Aves: Elaninae) with Taxonomic Implications.
Diversity 12(9): 327
doi: https://doi.org/10.3390/d12090327

Kites of the Elaninae group are small and medium-sized, mostly tropical raptors traditionally considered as an early diverged subfamily of the Accipitridae. We used nucleotide sequences of three genetic markers (mitochondrial Cyt b and COI, nuclear RAG-1) to reconstruct the phylogenetic relationships of the Elaninae, other kites, and representatives of different families of diurnal raptors. Our results confirm the basal position of Elaninae, separated the latest in Early Miocene, including Chelictinia riocourii, which was not sequenced before and belongs to this group. Not only DNA data but also cytological, morphological, and ecological data show the singularity of Elaninae. We suggest elevating this group to family level as Elanidae within the order Accipitriformes. It includes Gampsonyx swainsonii as a monotypic subfamily because of distinctive traits and DNA sequence data. Taxonomic implications for other macrogroups of Accipitriformes are discussed.


Free pdf:

AnaÃs Duhamel, Julian P. Hume, Pauline Guenser, CÃline Salaviale & Antoine Louchart (2020)
Cranial evolution in the extinct Rodrigues Island owl Otus murivorus (Strigidae), associated with unexpected ecological adaptations.
Scientific Reports Â10, Article number: 14019
DOI: https://doi.org/10.1038/s41598-020-69868-1

Island birds that were victims of anthropic extinctions were often more specialist species, having evolved their most distinctive features in isolation, making the study of fossil insular birds most interesting. Here we studied a fossil cranium of the âgiantâ extinct scops owl Otus murivorus from Rodrigues Island (Mascarene Islands, southwestern Indian Ocean), to determine any potential unique characters. The fossil and extant strigids were imaged through X-ray microtomography, providing 3D views of external and internal (endocast, inner ear) cranial structures. Geometric morphometrics and analyses of traditional measurements yielded new information about the Rodrigues owlâs evolution and ecology. Otus murivorus exhibits a 2-tier âlag behindâ phenomenon for cranium and brain evolution, both being proportionately small relative to increased body size. It also had a much more developed olfactory bulb than congeners, indicating an unexpectedly developed olfactory sense, suggesting a partial food scavenging habit. In addition, O. murivorus had the eyes placed more laterally than O. sunia, the species from which it was derived, probably a side effect of a small brain; rather terrestrial habits; probably relatively fearless behavior; and a less vertical posture (head less upright) than other owls (this in part an allometric effect of size increase). These evolutionary features, added to gigantism and wing reduction, make the extinct Rodrigues owlâs evolution remarkable, and with multiple causes.

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