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Abstract
A series of crosses was made involving lightly-, and heavily-, and non-feather-shanked chickens in an attempt to clear up the confusion in the literature concerning the inheritance of feathered shanks in chickens. The Langshan and Brahma breeds were both shown to possess the same single shank-feathering locus, but because of their differences in phenotype and penetrance in the genetic crosses it was suggested that they possessed different alleles at this locus. This locus was designated as Pti-1, with Pti-1L being the Langshan allele and Pti-1B the Brahma allele. The Brahma allele was shown to be dominant over the Langshan allele. Both the Sultan and Cochin breeds were shown to possess two shank-feathering loci, and the data suggested that one of the loci in the Sultan contained the Pti-1L allele. It is hypothesized that the comparable allele in the Cochin breed was Pti-1B. It is proposed that the second locus in both of these breeds is similar, and the symbol Pti-2 is suggested.
... Clean leg (lacking feathers) may in fact be the derived state in birds because many basal birds have feathered legs and the "4-winged" dinosaurs had feathered hindlimbs (Xu and Zhang 2005;Hu et al. 2009;Hone et al. 2010). Feathered leg is an attractive trait in fancy chicken breeding, with leg feathering in such breeds ranging from sparse like in Langshan chickens to extensive like in the Cochin breed (Somes 1992). Poultry geneticists have studied the inheritance of feathered legs since the beginning of the last century (Punnett and Bailey 1918;Dunn and Jull 1927;Warren 1933). ...
... Poultry geneticists have studied the inheritance of feathered legs since the beginning of the last century (Punnett and Bailey 1918;Dunn and Jull 1927;Warren 1933). Somes (1992), based on the results of test mating, provided genetic evidence for the presence of two independent dominant mutations, denoted Pti-1 and Pti-2, causing feathered legs in domestic chicken. Breeds with more sparsely feathered legs were supposed to be homozygous mutant at the Pti-1 locus but wild-type (pti-2/pti-2) at the second locus. ...
... Breeds with more sparsely feathered legs were supposed to be homozygous mutant at the Pti-1 locus but wild-type (pti-2/pti-2) at the second locus. Breeds with more heavily feathered legs like Sultan and Cochin were thought to carry the dominant mutations at both Pti-1 and Pti-2 (Somes 1992). A recessive allele (pti-3) at a third locus has been suggested to cause leg feathering in the Pavloff chicken (Somes 1990). ...
Feathered leg is a trait in domestic chickens that has undergone intense selection by fancy breeders. Previous studies have shown that two major loci controlling feathered leg are located on chromosomes 13 and 15. Here we present genetic evidence for the identification of candidate causal mutations at these loci. This was accomplished by combining classical linkage mapping using an experimental cross segregating for feathered leg and high-resolution identical-by-descent mapping using whole genome sequence data from 167 samples of chicken with or without feathered legs. The first predicted causal mutation is a single base change located 25 kb upstream of the gene for the forelimb-specific transcription factor TBX5 on chromosome 15. The second is a 17.7 kb deletion located about 200 kb upstream of the gene for the hindlimb-specific transcription factor PITX1 on chromosome 13. These mutations are predicted to activate TBX5 and repress PITX1 expression, respectively. The study reveals a remarkable convergence in the evolution of the feathered leg phenotype in domestic chickens and domestic pigeons as this phenotype is caused by non-coding mutations upstream of the same two genes. Furthermore, the PITX1 causal variants are large overlapping deletions, 17.7 kb in chicken and 44 kb in pigeons. The results of the present study are consistent with the previously proposed model for pigeon, that feathered leg is caused by reduced PITX1 expression and ectopic expression of TBX5 in hindlimb buds resulting in a shift of limb identity from hindlimb to more forelimb-like identity.
... Classical genetic studies implicate at least two loci in heavy foot feathering in chickens (Punnett and Bailey, 1918;Lambert and Knox, 1929;Warren, 1948;Somes, 1992), although the molecular genetic origins of the trait remain unknown. Previously, a chromosome region containing Pitx1 was implicated in foot feathering in silkie chickens (Dorshorst et al., 2010). ...
... This apparent conflict could be because the causative gene in silkies is not actually Pitx1 but rather a gene closely linked to it, or because Pitx1 expression differences are more pronounced and consistent at developmental stages that we did not assay. Furthermore, different populations of breeds such as silkies appear to have different constellations of ptilopody loci and alleles, and it is possible that we used strains that do not have Pitx1 mutations (Wexelsen, 1934;Somes, 1992). Also in contrast to our results in feather-footed pigeons, Tbx3 was not upregulated in ptilopodous chicken breeds (white leghorn 1 ± 0.17, silkie 0.48 ± 0.18, p=0.004; ...
Birds display remarkable diversity in the distribution and morphology of scales and feathers on their feet, yet the genetic and developmental mechanisms governing this diversity remain unknown. Domestic pigeons have striking variation in foot feathering within a single species, providing a tractable model to investigate the molecular basis of skin appendage differences. We found that feathered feet in pigeons result from a partial transformation from hindlimb to forelimb identity mediated by cis-regulatory changes in the genes encoding the hindlimb-specific transcription factor Pitx1 and forelimb-specific transcription factor Tbx5. We also found that ectopic expression of Tbx5 is associated with foot feathers in chickens, suggesting similar molecular pathways underlie phenotypic convergence between these two species. These results show how changes in expression of regional patterning genes can generate localized changes in organ fate and morphology, and provide viable molecular mechanisms for diversity in hindlimb scale and feather distribution.
... For the feathered feet trait, two loci were identified in a previous study (Somes 1992). Other feather traits were investigated by Noorai et al (2012), who found that the rumpless and ear-tufted traits loci were located on chicken chromosomes 2 and 15, respectively. ...
... In many breeds of domestic chicken, such as the Silky and Beijing-You chicken, a mutative transformation of scales to feathers on the tarsus, feet and toes, the so-called feathered feet trait (ptilopody), has become a breed characteristic (Bartels 2003). In a previous study, two QTL for the feathered feet trait were identified (Somes 1992), but the physical positions of these two QTL were not found. In this study, two QTL regions, 55 cM/1.56 ...
Physical appearance traits, such as feather-crested head, comb size and type, beard, wattles size and feathered feet, are used to distinguish between breeds of chicken, and may also be associated with economic traits. In this study, a genome-wide linkage analysis was used to identify candidate regions and genes for physical appearance traits and to potentially provide further knowledge of the molecular mechanisms that underlie these traits. The linkage analysis was conducted with an F2 population derived from Beijing-You chickens and a commercial broiler line. Single nucleotide polymorphisms (SNPs) were analyzed using the Illumina 60K Chicken SNP Beadchip. The data were used to map quantitative trait loci (QTLs) and genes for six physical appearance traits. A 10 cM/0.51 Mb region (0.0-10.0 cM/0.00-0.51 Mb) with 1% genome-wide significant level on LGE22C19W28_E50C23 linkage group (LGE22) for crest trait was identified, which is likely very closely linked to the HOXC8. A QTL with 5% chromosome-wide significant level for comb weight, which partly overlaps with a region identified in a previous study, was identified at 74cM/25.55 Mb on chicken (Gallus gallus) chromosome 3 (GGA3). For beard and wattles traits, a same region 11 cM/2.23 Mb (0.0-11.0 cM/0.00-2.23 Mb) including WNT3 and GH genes on GGA27 was identified. Two QTLs with 1% genome-wide significant level for feathered feet trait, one 9 cM/2.80 Mb (48.0-57.0/13.40-16.20 Mb) region on GGA13 and another 12 cM/1.45 Mb (41.0-53.0 cM/11.37-12.82 Mb) region on GGA15 were identified. These candidate regions and genes provide important genetic information for the physical appearance traits in chicken.
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... There are several chicken breeds that exhibit extensive feather formation along the shank and digits (e.g., Bantams, Cochins, and Silkies) that also provide useful models for study of the initial induction of epidermal organs of chick. The allele(s) involved in these traits affect both the mesenchyme and epidermis as shown in recombination studies (Goetinck, 1967;Somes, 1992). The molecular nature of these alleles is not known nor are the signaling systems or developmental processes that they disrupt. ...
... The ptilopodous phenotype of the Silkie breed is due to a dominant allele (Pti) that causes feathering of the shanks and toes (Somes, 1992). Feathering on the shank in Silkie occurs in a developmental sequence starting from digit 4 and the proximal metatarsal and subsequently across the foot toward digit 3 (Fig. 6A). ...
The induction and specification of a large number of vertebrate organs require reciprocal signaling between an epithelium and subjacent mesenchyme. In the formation of integumentary organs, the initial inductive signaling events leading to the formation of the organ primordia stem from the mesenchyme. However, the epithelium must have the capacity to respond to these signals. We demonstrate that bone morphogenetic protein 7 (Bmp7) is an early molecular marker for epidermal organ development during development of feathers and scales of the chick. Bmp7 is expressed broadly in the preplacode epidermis and subsequently becomes localized to the forming placodes of feathers and scales. An examination of Bmp7 expression in the scaleless mutant chicken integument indicates that Bmp7 expression in the epidermis is associated with the ability to form epidermal organs. We show that BMP7 function is necessary for the formation of epidermal placodes in both feather and scale forming epidermis. In addition, precocious expression of Bmp7 in the metatarsal epidermis of the Silkie mutant or treatment of the metatarsus with ectopic BMP7 protein results in feather development from scale forming integument. From these data, we propose that Bmp7 is necessary and sufficient, in a developmental context, to mediate the competence of an epithelium to respond to inductive signals from the underlying mesenchyme to form epidermal organs in the chick. We propose that regulation of Bmp7 in localized areas of the embryonic epidermis facilitates the development of regional formation of integumentary organs.
... The inheritance of the shank feathering trait in chicken has been studied by many poultry researchers (Danforth 1919;Lambert and Knox 1929;Warren 1949). A nonfeathering shank is a dominant trait in chicken, and it has been proposed that two factors such as PTI-1L and PTI-1B are responsible (Somes 1992). Up to date, chromosomes 13, 15 and 24 are the candidate chromosomal locations for this trait (Moiseeva et al. 2012). ...
The rational of conservation and sustainable use of indigenous chicken (IC) resources requires their morphobiometrical characterisation. This study morphobiometrically characterised the IC ecotypes in Rwanda. The morphological features and zoometric measurement data were randomly collected on 1670 mature IC of both sexes from five ecotypes of Rwanda. The nonparametric Kruskal–Wallis and Mann–Whitney U test were used in evaluating the effect of ecotypes on the qualitative morphological variables. Zoometric measurements were analysed with the PROC GLM of SAS. The findings showed that the feather morphology and distribution were mainly normal (98.3 and 84.40%, respectively) while feather colour was dominated with multicoloured (38.10%). The majority of the birds had red earlobe (49.20%), yellow shanks (53.80%) and single comb-type (71.70%). These parameters were different (p < 0.05) between the ecotypes. Bodyweight and linear body measurements were highly different (P < 0.001) between ecotypes. Differences associated with sex (P < 0.001) were observed in body weight and linear body measurements. The interaction between ecotype and sex significantly (P < 0.001) influenced body weight, body length, shank length, comb length, comb height, wattle length, chest circumference, neck length and wingspan. The IC ecotypes in Rwanda were found to be diverse morphobiometrically both in quantitative and qualitative traits. These variations provide a foundation for classification of the chicken into breeds.
... Serebrovsky (1926) suggested at least two dominant and at least two recessive feathered shank genes. Somes (1992) described two loci, PTII and PT12. PT11 has two alleles, the Langshan allele (PTII*L) and the Brahma allele ...
... Producing a chicken with a clean shank could be addressed over several generations. This was because feathered shank (ptilopody), located on chromosome 13, was multi-allelic (Somes, 1992), and there were modifiers that had to be addressed (Hutt, 1949). Early writers confirm that selection of cleanlegged birds was necessary during the foundation of the Barred Plymouth Rock (Procter, 1911). ...
Crossing of populations has been, and still is, a central component in domestication and breed and variety formation. It is a way for breeders to utilize heterosis and to introduce new genetic variation into existing plant and livestock populations. During the mid-19th century, several chicken breeds that had been introduced to America from Europe and Asia became the founders for those formed in the USA. Historical records about the genealogy of these populations are often unclear and inconsistent. Here, we used genomics in an attempt to describe the ancestry of the White Plymouth Rock (WPR) chicken. In total, 150 chickens from the WPR and 8 other stocks that historical records suggested contributed to its formation were whole-genome re-sequenced. The admixture analyses of the autosomal and sex chromosomes showed that the WPR was likely founded as a cross between a paternal lineage that was primarily Dominique, and a maternal lineage where Black Java and Cochin contributed in essentially equal proportions. These results were consistent and provided quantification with the historical records that they were the main contributors to the WPR. The genomic analyses also revealed genome-wide contributions (<10% each) by Brahma, Langshan, and Black Minorca. When viewed on an individual chromosomal basis, contributions varied considerably among stocks.
... The inheritance of the shank feathering trait has been studied by many poultry researchers including chicken (Danforth, 1919;Lambert & Knox, 1929;Warren, 1949), pidgeon (Wexelsen, 1933), and hawk (Ellis et al., 1999). Nonfeathering shank is a dominant trait in chicken and it has been proposed that two factors are responsible (pti-1 L , pti-1 B ) (Somes, 1992). Up to date, chromosomes 13, 15, and 24 (Moiseyeva et al., 2012) are the candidate chromosomal location for this trait. ...
Chicken eggs represent an important source of protein to the growing
human population and also supply repositories of unique genes that
could be used worldwide. The inheritance of shank feathering trait is
dominant upon non-feathering shank trait in chicken which is based on
two factors: pti-1L and pti-1B that are located on Chromosomes 13, 15,
and 24. Using 185 fertile eggs collected from two genetic lines (shank
feathering and non-feathering shank) of White Kurdish chicken, we
found that egg weight highly (P < 0.01) correlated with yolk weight
(r2=0.520, 0.704, respectively), albumen weight (r2=0.918, 0.835), and
shell weight (r2=0.626, 0.225). The first two principal components
explained the greatest variance in both the White with shank feathering
(85.6% of total variance) and non-feathering shank (76.5%). Therefore,
differences in the component traits of the eggs between the two genetic
lines may be influenced by the same gene actions as shank feathering
trait. According to these results, the two genetic lines of Kurdish
chicken yield significant differences in the internal traits of eggs.
... Extensive classical breeding experiments in both pigeons and chickens have demonstrated that foot feathering is controlled by a relatively small number of genetic loci of large effect (Doncaster, 1912;Hollander, 1937;Levi, 1986;Somes, 1992;Wexelsen, 1934). In more recent work, Dorshorst et al. (2010) and Sun et al. (2015) used SNP-phenotype associations to identify genomic regions associated with a variety of morphological features in chickens, including ptilopody. ...
Variation in regional identity, patterning, and structure of epidermal appendages contributes to skin diversity among many vertebrate groups, and is perhaps most striking in birds. In pioneering work on epidermal appendage patterning, John Saunders and his contemporaries took advantage of epidermal appendage diversity within and among domestic chicken breeds to establish the importance of mesoderm-ectoderm signaling in determining skin patterning. Diversity in chickens and other domestic birds, including pigeons, is driving a new wave of research to dissect the molecular genetic basis of epidermal appendage patterning. Domestic birds are not only outstanding models for embryonic manipulations, as Saunders recognized, but they are also ideal genetic models for discovering the specific genes that control normal development and the mutations that contribute to skin diversity. Here, we review recent genetic and genomic approaches to uncover the basis of epidermal macropatterning, micropatterning, and structural variation. We also present new results that confirm expression changes in two limb identity genes in feather-footed pigeons, a case of variation in appendage structure and identity.
... This epidermal variability is reminiscent of interspecific variation among wild birds, as some raptor and boreal species have feathered feet (e.g., some ptarmigans and owls). Previous studies of chicken development and genetics suggest changes in dermal-epidermal interactions as a mechanism governing the decision between scaled and feathered epidermis (Chang et al., 2004;Crowe et al., 1998;Dorshorst et al., 2010;Harris et al., 2002;Harris et al., 2004;Somes, 1992;Zou and Niswander, 1996). Recent findings about the molecular basis of epidermal variation in pigeons, however, suggest a more fundamental developmental basis (Domyan et al., 2016). ...
Intensive artificial selection over thousands of years has produced hundreds of varieties of domestic pigeon. As Charles Darwin observed, the morphological differences among breeds can rise to the magnitude of variation typically observed among different species. Nevertheless, different pigeon varieties are interfertile, thereby enabling forward genetic and genomic approaches to identify genes that underlie derived traits. Building on classical genetic studies of pigeon variation, recent molecular investigations find a spectrum of coding and regulatory alleles controlling derived traits, including plumage color, feather growth polarity, and limb identity. Developmental and genetic analyses of pigeons are revealing the molecular basis of variation in a classic example of extreme intraspecific diversity, and have the potential to nominate genes that control variation among other birds and vertebrates in general.
... A few key characteristics of chicken, including its vast economic importance in food production, human-like diseases, and manipulability of the embryos, have facilitated research into topics of importance for agriculture, medicine, and fundamental biology [2]. After domestication, spontaneous mutations in chickens have led to various phenotypic variations, such as Crest (Cr) [3], Naked neck (Nc) [4], Scaleless (Sc) [5], Frizzle (Fr) [6], Silky (H) [7], Ear tufts (Et) [8], Ptilopody or feathered shank (Pti) [9], Vulture hocks (Vh) [9,10], and Muffs and beard (Mb) [11]. Until now, several mutations underlying these phenotypic variations have been identified. ...
Muffs and beard (Mb) is a phenotype in chickens where groups of elongated feathers gather from both sides of the face (muffs) and below the beak (beard). It is an autosomal, incomplete dominant phenotype encoded by the Muffs and beard (Mb) locus. Here we use genome-wide association (GWA) analysis, linkage analysis, Identity-by-Descent (IBD) mapping, array-CGH, genome re-sequencing and expression analysis to show that the Mb allele causing the Mb phenotype is a derived allele where a complex structural variation (SV) on GGA27 leads to an altered expression of the gene HOXB8. This Mb allele was shown to be completely associated with the Mb phenotype in nine other independent Mb chicken breeds. The Mb allele differs from the wild-type mb allele by three duplications, one in tandem and two that are translocated to that of the tandem repeat around 1.70 Mb on GGA27. The duplications contain total seven annotated genes and their expression was tested during distinct stages of Mb morphogenesis. A continuous high ectopic expression of HOXB8 was found in the facial skin of Mb chickens, strongly suggesting that HOXB8 directs this regional feather-development. In conclusion, our results provide an interesting example of how genomic structural rearrangements alter the regulation of genes leading to novel phenotypes. Further, it again illustrates the value of utilizing derived phenotypes in domestic animals to dissect the genetic basis of developmental traits, herein providing novel insights into the likely role of HOXB8 in feather development and differentiation.
... As is so often the case, mutations affecting feather formation have proven very useful for understanding feather development. Do the chicken lineages that display "feathered feet" (Abbott, 1965;Goetinck, 1967;Sawyer, 1970;Somes, 1971Somes, , 1992Brotman, 1976;Altman and Katz, 1979) provide information concerning the proposed role of the embryonic layers in the origin of feathers? ...
The formation of scales and feathers in reptiles and birds has fascinated biologists for decades. How might the developmental processes involved in the evolution of the amniote ectoderm be interpreted to shed light on the evolution of integumental appendages? An Evo-Devo approach to this question is proving essential to understand the observation that there is homology between the transient embryonic layers covering the scale epidermis of alligators and birds and the epidermal cell populations of embryonic feather filaments. Whereas the embryonic layers of scutate scales are sloughed off at hatching, that their homologues persist in feathers demonstrates that the predecessors of birds took advantage of the ability of their ectoderm to generate embryonic layers by recruiting them to make the epidermis of the embryonic feather filament. Furthermore, observations on mutant chickens with altered scale and feather development (Abbott and Asmundson [1957] J. Hered. 18:63-70; Abbott [1965] Poult. Sci. 44:1347; Abbott [1967] Methods in developmental biology. New York: Thomas Y. Crowell) suggest that the ectodermal placodes of feathers, which direct the formation of unique dermal condensations and subsequently appendage outgrowth, provided the mechanism by which the developmental processes generating the embryonic layers diverged during evolution to support the morphogenesis of the epidermis of the primitive feather filament with its barb ridges.
A total of twenty-six local chickens were representing shank feathering and non-feathering shank were used to sequence five QTLs, which associated with shank feather trait in chicken. The five location sequence results were shown polymorphism between the shank feathering and non-feathering shank. All the candidate markers were differed between the shank feather and non-feathering shank. The big distance was in (ADL221), and the less distance was in marker MCW315.
The feather is a complex ectodermal organ with hierarchical branching patterns. It provides functions in endothermy, communication, and flight. Studies of feather growth, cycling, and health are of fundamental importance to avian biology and poultry science. In addition, feathers are an excellent model for morphogenesis studies because of their accessibility, and their distinct patterns can be used to assay the roles of specific molecular pathways. Here we review the progress in aspects of development, regeneration, and evolution during the past three decades. We cover the development of feather buds in chicken embryos, regenerative cycling of feather follicle stem cells, formation of barb branching patterns, emergence of intrafeather pigmentation patterns, interplay of hormones and feather growth, and the genetic identification of several feather variants. The discovery of feathered dinosaurs redefines the relationship between feathers and birds. Inspiration from biomaterials and flight research further fuels biomimetic potential of feathers as a multidisciplinary research focal point. Expected final online publication date for the Annual Review of Animal Biosciences Volume 3 is February 15, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
The skin displays marked anatomical variation in thickness, colour and in the appendages that it carries. These regional distinctions arise in the embryo, likely founded on a combinatorial positional code of transcription factors. Throughout adult life, the skin's distinct anatomy is maintained through both cell autonomous epigenetic processes and by mesenchymal-epithelial induction. Despite the readily apparent anatomical differences in skin characteristics across the body, several fundamental questions regarding how such regional differences first arise and then persist are unresolved. However, it is clear that the skin's positional code is at the molecular level far more extensive than that discernible at the phenotypic level. This provides a latent reservoir of anatomical complexity ready to surface if perturbed by mutation, hormonal changes, ageing or experiment.
Chicken gene inheritance analysis, started one century ago, had led to the development of the classical genetic map. Efforts and legacy of the previous geneticists' generations are not forgotten and constitute the fundamentals of contemporary genome research progress. Advances in molecular biology, cytogenetics and DNA technologies provided more powerful and sophisticated tools to tackle chicken gene mapping and genome research problems. In the 1990s configurations of chicken molecular and cytogenetic maps had begun standing out. New horizons in chicken genomics are opening with application of BAC libraries, BAC-contig physical maps, ESTs and whole genome sequencing. The chicken has been a notable experimental model for several fundamental and applied biologic disciplines in the last century, and will remain such in the 21st century. The upcoming complete genome sequencing combined with discovering gene functions will facilitate the improvement of traits of economic importance and value in poultry.
Genomics research on animals has generated huge databases and several new concepts and strategies, which are used to elucidate origin, evolution and phylogeny of species. Genetic and physical maps of genomes give details on chromosomal location, function, expression and regulation of genes. The series Genome Mapping and Genomics in Animals provides comprehensive and up-to-date reviews on genomic research on selected animal systems contributed by leading scientists from around the world.
This volume offers information on gene mapping and genomics research in domesticated and farmed animals including cattle, water buffalo, sheep, deer, poultry, turkeys, rabbits, dogs and pigs. While the genome maps for some species are very limited, full genome sequences are available for cattle, chickens and dogs. Genomic research contributes to the identification of genetic regions that control the functionality and well-being of animals. Several farmed species are also used as models for biomedical studies.
The discovery of several dinosaurs with filamentous integumentary appendages of different morphologies has stimulated models for the evolutionary origin of feathers. In order to understand these models, knowledge of the development of the avian integument must be put into an evolutionary context. Thus, we present a review of avian scale and feather development, which summarizes the morphogenetic events involved, as well as the expression of the beta (beta) keratin multigene family that characterizes the epidermal appendages of reptiles and birds. First we review information on the evolution of the ectodermal epidermis and its beta (beta) keratins. Then we examine the morphogenesis of scutate scales and feathers including studies in which the extraembryonic ectoderm of the chorion is used to examine dermal induction. We also present studies on the scaleless (sc) mutant, and, because of the recent discovery of "four-winged" dinosaurs, we review earlier studies of a chicken strain, Silkie, that expresses ptilopody (pti), "feathered feet." We conclude that the ability of the ectodermal epidermis to generate discrete cell populations capable of forming functional structural elements consisting of specific members of the beta keratin multigene family was a plesiomorphic feature of the archosaurian ancestor of crocodilians and birds. Evidence suggests that the discrete epidermal lineages that make up the embryonic feather filament of extant birds are homologous with similar embryonic lineages of the developing scutate scales of birds and the scales of alligators. We believe that the early expression of conserved signaling modules in the embryonic skin of the avian ancestor led to the early morphogenesis of the embryonic feather filament, with its periderm, sheath, and barb ridge lineages forming the first protofeather. Invagination of the epidermis of the protofeather led to formation of the follicle providing for feather renewal and diversification. The observations that scale formation in birds involves an inhibition of feather formation coupled with observations on the feathered feet of the scaleless (High-line) and Silkie strains support the view that the ancestor of modern birds may have had feathered hind limbs similar to those recently discovered in nonavian dromaeosaurids. And finally, our recent observation on the bristles of the wild turkey beard raises the possibility that similar integumentary appendages may have adorned nonavian dinosaurs, and thus all filamentous integumentary appendages may not be homologous to modern feathers.
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