Ben Creisler
Some recent avian papers:
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Background
Vertebrates possess a diverse range of integumentary epithelial appendages, including scales, feathers and hair. These structures share extensive early developmental homology, as they mostly originate from a conserved anatomical placode. In the context of avian epithelial appendages, feathers and scutate scales are known to develop from an anatomical placode. However, our understanding of avian reticulate (footpad) scale development remains unclear.
Results
Here, we demonstrate that reticulate scales develop from restricted circular domains of thickened epithelium, with localised conserved gene _expression_ in both the epithelium and underlying mesenchyme. These domains constitute either anatomical placodes, or circular initiatory fields (comparable to the avian feather tract). Subsequent patterning of reticulate scales is consistent with reactionâdiffusion (RD) simulation, whereby this primary domain subdivides into smaller secondary units, which produce individual scales. In contrast, the footpad scales of a squamate model (the bearded dragon, Pogona vitticeps) develop synchronously across the ventral footpad surface.
Conclusions
Widely conserved gene signalling underlies the initial development of avian reticulate scales. However, their subsequent patterning is distinct from the footpad scale patterning of a squamate model, and the feather and scutate scale patterning of birds. Therefore, we suggest reticulate scales are a comparatively derived epithelial appendage, patterned through a modified RD system.
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?Crossvallia waiparensis, sp. nov.Â
We describe a new large-sized species of the Sphenisciformes (penguins) from Paleocene strata of the Waipara Greensand in New Zealand. ?Crossvallia waiparensis, sp. nov. is represented by leg bones of a single individual as well as two tentatively referred proximal humeri and resembles Crossvallia unienwillia from the late Paleocene of Antarctica in size and morphology. The new species is the fifth published species of stem group Sphenisciformes from the Waipara Greensand and the fourth one, which has been formally named. It is distinguished from a recently reported tarsometatarsus of an unnamed large-sized penguin species from the Waipara Greensand and is the oldest well-represented giant penguin. ?C. waiparensis approaches the size of the Eocene taxa Anthropornis and Palaeeudyptes and provides further evidence that penguins attained a very large size early in their evolutionary history.
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Although the avian family Anhingidae is unequivocally monophyletic, the number and relationships of the component species within the single genus (Anhinga) have long remained unclear. Here, we use extensive mitochondrial and nuclear DNA sequence data (8,878 bp) to show that four species should be recognized. Our fully resolved and wellâsupported tree shows that the American Anhinga (Anhinga anhinga) is sister to the three Old World species, with the Oriental (A. melanogaster) and African (A. rufa) Darters sister within the Old World clade, which also includes the Australian Darter (A. novaehollandiae). We estimate that the divergence between the New World and Old World branches occurred 19-22 mya, with the Australian Darter separating from its Old World congeners 14-16 mya and the Oriental and African species splitting ~10 mya. The genus is yet another example of osteological conservatism in the Suliformes, which is comparable to that shown by the cormorants and shags. Nevertheless, the relationships we infer are congruent with recent plumage studies and are biogeographically plausible. We suggest that further investigation of the variation within the African and Australian Darters would be of interest.
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Also may be of interest:
Free pdf:
Esteban FernÃndez-Juricic, ÂPatrice E. Baumhardt, ÂLuke P. Tyrrell, ÂAmanda Elmore, ÂShelagh T. DeLiberto & Scott J. Werner (2019)
Vision in an abundant North American bird: The Red-winged Blackbird.
The Auk: ukz039 (advance online publication)
doi:
https://doi.org/10.1093/auk/ukz039https://academic.oup.com/auk/advance-article/doi/10.1093/auk/ukz039/5549081 Avian vision is fundamentally different from human vision; however, even within birds there are substantial between-species differences in visual perception in terms of visual acuity, visual coverage, and color vision. However, there are not many species that have all these visual traits described, which can constrain our ability to study the evolution of visual systems in birds. To start addressing this gap, we characterized multiple traits of the visual system (visual coverage, visual acuity, centers of acute vision, and color vision) of the Red-winged Blackbird (Agelaius phoeniceus), one of the most abundant and studied birds in North America. We found that Red-winged Blackbirds have: wide visual coverage; one center of acute vision per eye (fovea) projecting fronto-laterally with high density of single and double cones, making it the center of both chromatic and achromatic vision; a wide binocular field that does not have the input of the centers of acute vision; and an ultraviolet sensitive visual system. With this information, we parameterized a Red-winged Blackbird-specific perceptual model considering different plumage patches. We found that the male red epaulet was chromatically conspicuous but with minimal achromatic signal, but the male yellow patch had a lower chromatic but a higher achromatic signal, which may be explained by the pigment composition of the feathers. However, the female epaulet was not visually conspicuous in both the chromatic and achromatic dimensions compared with other female feather patches. We discuss the implications of this visual system configuration relative to the foraging, antipredator, mate choice, and social behaviors of Red-winged Blackbirds. Our findings can be used for comparative studies as well as for making more species-specific predictions about different visual behaviors for future empirical testing.