Scale embryogenesis in birds and reptiles. Such hypothetic dermal condensations may have re-utilized the Wnt/beta-catenin system, first present in teeth, in skin formation, leading to the formation of long tubular outgrowths, somewhat similar to the long bristles of the tail of Psittacosaurus (Mayr et al. The next visible step of skin differentiation has been well studied, mostly in birds. Chuong C-M, Chodankar R, Widelitz RB, Jiang T-X. 1996; Logan et al. A single fiber, or hair shaft, is produced by the hair follicle, which can be compared to the barb, the basic element of the feather. The ability to form epidermal glands and a first thin, protective layer against desiccation, adorned with alpha-keratinized bumps may have appeared with the early terrestrial tetrapods, a condition that has probably been conserved in some living amphibians, e.g. This is the first evidence in mammals for a classic pattern in nature called Bogert's Rule, which states that dark colors could aid with thermoregulation as they help absorb heat from the sun's rays. 2004), and (2) when beta-catenin is over-expressed in mouse embryo epidermis (Fig. Hairs began to protrude through the follicles (as seen in rat tails today). But, he says, the reality is much simpler. Clues from a mutant lizard inspired Milinkovitchs team to probe the mystery. Julian Muoz has a ruler that could size up the early universe, A star cluster in the Milky Way appears to be as old as the universe, Physicists split bits of sound using quantum mechanics, One photon is all it takes to kick off photosynthesis, all three structures evolved from a shared ancestor, also active in the skin of developing alligators, The anatomical placode in reptile scale morphogenesis indicates shared ancestry among skin appendages in amniotes, Nuclear -catenin localization supports homology of feathers, avian scutate scales, and alligator scales in early development, Ancient reptiles saw red before turning red, Rare reptile holds clue to penis evolution, Sunbirds dazzling feathers are hot, in both senses of the word, Bottlenose dolphin moms use baby talk with their calves, DNA has revealed the origin of this giant mystery gecko, How understanding horses could inspire more trustworthy robots, Polyester bees brew beer-scented baby food in plastic cribs, Camouflaging wheat with a wheat smell could be a new approach to pest control, Bowhead whales may have a cancer-defying superpower: DNA repair, RNA editing helps octopuses cope with the cold. The Ancient Armor of Fish - Scales - Provide Clues to Hair, Feather Get weekly and/or daily updates delivered to your inbox. insulate, as underfur thickens and thermoregulation matures. The mouse Engrailed-1 gene and ventral limb patterning. This epithelium is characterized by the expression of Pax6, the eye master gene, and by a pair of keratins, K12/K3. Gregg K, Rogers GE. 2004). Thus, by manipulating chick or mouse embryos in this manner, parallel effects have been obtained. The bottom portion of the hair peg forms the hair matrix, which is overlaid by the first conical inner root sheath. However, although the claws of squamates are principally made of beta-keratins, recent results show that they can also contain a few cysteine-rich alpha-keratins, and thus some hair-like proteins (Eckhart et al. The differentiation of prospective thigh mesoderm grafted beneath the apical ectodermal ridge of the wing bud in the chick embryo. Thesleff I. Epithelial-mesenchymal signalling regulating tooth morphogenesis. For a long time the non-mammalian parts of this family tree like the sail-backed Dimetrodon and weasel-like cynodonts were called mammal-like reptiles, but this was off the mark. Science Advances. Lepidosaurs and archosaurs are diapsids, but the chelonian are anapsids, and their relationships with regard to the other sauropsids are still debated. In the chick embryo, the future feather first appears on the back as a round primordium, composed of a placode overlying a dermal condensation by day 7. This is even true with the fine sandstones of the Liaoning province of China. Furthermore, studies of epidermal stem cells differentiation showed that the level of beta-catenin controls their lineage, i.e. Although the external shape of avian reticula bears some resemblance to the hypothetic granulated integument of first archosaurs, they are made only of alpha-keratins and are therefore not directly related. Reproduced with permission of the Company of Biologists. In the two following sections I will propose my detailed view concerning the scenario of feather, avian scales, hair and mammary glands origins, which is summarized in Fig. As to the early evolution of mammalian hair, Rowe et al. In particular, birds exhibit scaled feet and mammals are not only characterized by hairs, but also by the large number and diversification of their cutaneous glands. Did human hairs actually evolve from scales? Thank you for visiting nature.com. OGuin WM, Galvin S, Schermer A, Sun TT. In eutherians, the mammary gland became secondarily independent of hair. Prum RO. Houzelstein D, Cheraud Y, Auda-boucher G, Fontaine-Perus J, Robert B. What Makes Archaeopteryx Fossils the Bizarre Bridge Between Dinos and Birds? Skin from a fetal bearded dragon lizard shows a developing bump (white arrow, top panel) 20 days after the egg was laid. A special regulation event happens for the plantar face of the feet in both classes (Loomis et al. If fur truly did evolve from scales as was once believed, we would find many different varieties of it in fossils. Using hand-waving arguments, one could argue that the first placodes that evolved in stem reptiles might have . 6B). The discovery of many intermediate forms of feather-like appendages in the northern part of China, brought many new insights in the evolution of feathers (reviewed in Chuong et al. Xu X, Wang XL, Wu XC. The latter sustained a long outgrowth of the hair shaft. Meanwhile, a dragon carrying two copies of a natural EDA mutation (one from mom, one from dad) becomesscaleless. Sign up for our email newsletter for the latest science news, Want More? I am indebted to Drs. Sharpe PT. 1999, 2001; Brush, 2000). Did they evolve from scales? In CP/M, how did a program know when to load a particular overlay? The explanation is that retinoic acid treatment, which enhances Shh expression in the epidermis, leads to the formation of feathers on reticula, bypassing the earlier ectoderm down-regulation of Shh by En-1 (Prin & Dhouailly, 2004). Consequently, the epidermal potentiality is different in apteric and feathered regions from the epidermal ability in scaled regions. How many weeks of holidays does a Ph.D. student in Germany have the right to take? Dhouailly D. Formation of cutaceous appendages in dermo-epidermalrecombinations between reptiles, birds and mammals. Hair and feathers likely evolved in the Early Triassic ancestors of mammals and birds, at a time when synapsids and archosaurs show independent evidence of higher metabolic rates (erect gait and endothermy), as part of a major resetting of terrestrial ecosystems . Some speculations on the evolution of the vertebrate integument. And additional finds, including body impressions, suggest that the bellies of early synapsids were dotted with these same structures. Mammalian skin evolution: a re-evaluation. Prepare yourself. Thirty years later, I now believe that the same system has been independently re-utilized several times during amniote evolution. Multiple fossil finds are needed to clear up the ancestral protomammal state and when hair started to become a synapsid feature. Hair in mammals and feathers in birds have long been known to develop from placodespatches of thickened skin in embryos that are created by special cells known as columnar cells. Designer skin: lineage commitment in postnatal epidermis. 2000). Specifically, the researchers aimed to assess the impacts of climate, body size and color vision on hair evolution. The problem is that the fossil record isnt always obliging when it comes to direct evidence. These grafted cells are subsequently dragged distally from the induced skin by the movements and growth of the amnion. The morphogenesis of the scaled integument of reptiles is less well known than that of avian or mammalian skin. 2000). Mutations, by negatively regulating the local amount of beta-catenin, may have given rise to regional skin variations, depending on bird lineages: avian overlapping scales, as in chick feet, or glabrous skin, as on the neck of vultures. Evo-Devo of amniote integuments and appendages. Lillywhite HB. 1978; Dhouailly & Sawyer, 1984). Heres how you can help. 2004). Hairs, feathers and scales have a lot in common -- ScienceDaily 2008), activates not only the formation of placodes, but also the start of their differentiation. It is important to note the underlying redness and it is also important to note that all of the follicles in the photo are just single hairs. Prin F, Logan C, D'Souza D, Ensini M, Dhouailly D. Dorsal versus ventral scales and the dorsoventral patterning of chick foot epidermis. With the mammaliaform node, tooth replacement was diphyodont; suggesting the occurrence of lactation. or, by Tim Pierce, George Washington University. This interpretation creates understanding of why the complex formation of feathers at the tip of scuta is so easy to obtain in different types of experiments. 1B,B). 2001). 1984; Gregg & Rogers, 1986; Sawyer et al. Therefore, there are no distinct epidermal placodes and no dermal condensations in lizard scale formation. Some terrestrial species, such as mice, evolved footpads, which are deprived of hairs, but associated with isolated sweat glands. 2004a) or mouse (Fliniaux et al. 7 Traits Humans Inherited From Reptiles | Mental Floss So in this new study, published in the, Proceedings of the National Academy of Sciences, [subscription required], researchers ignored the fossil record and looked instead to the genetic record of living animals: namely, a chicken and an anole lizard. Finally, I will highlight the parallels between the regulation of the implicated pathways in birds (feathers vs. scales) and in mammals (hair vs. glands). 1990; Kanzler et al. ISSN 0028-0836 (print). These cells express the same developmental genes as bird and mammalian placodes, suggesting a common origin for modern hair, feathers and scales. The origin of the dorsal dermis from the somite dermomyotome has been traced in birds by chick/quail chimerae (Olivera-Martinez et al. These cells appear to migrate from the hair follicles and displace what remains of corneal epithelium. Not only their shape but also the set of keratins of each appendage type are different (Dhouailly et al. Taking together different experimental results that led to the scuta-feather metaplasia, I suggest the following scenario concerning the abilities of the anterior chick foot skin to form cutaneous appendages. 2007). Pangolins are within the clade Pholidota ( Tree of Life page for Eutheria) and their nearest relatives are anteaters, sloths, and armadillos. N. Di-Po and M. Milinkovitch. Agriculture Handbook 362. Only the sauropsids (birds and reptiles) possess an additional capacity for beta-keratin synthesis, an entirely different type of intermediate filament, which appears to result from a phylogenetic innovation that occurred after that of the alpha-keratins (Gregg & Rogers, 1986). Although the relationships of turtles are still controversial, they probably diverged from the other sauropsids after the innovation of beta-keratins. Studies in fetal Nile crocodiles, bearded dragon lizards and corn snakes appear to have settled a long-standing debate on the rise of skin coverings. Maderson PFA. This can occur in nature as shown by several cases of mutation in poultry (Somes, 1990). Dhouailly D, Rogers GE, Sengel P. The specification of feather and scale protein synthesis in epidermal-dermal recombinations. a, apterium; dd, dense dermis; ec, ectoderm; ep, epidermis; f, feather; fpr, feather primordial; g, glabrous; h, hair bud; me, mesenchyme; r, reticula; s, scuta; u, umbilical chord. 2000) that the beta-catenin level in the epidermis may be linked with the different types of epithelial outgrowth, scuta or feather development. A main difference exists during morphogenesis of scales, in lepidosaurs (Dhouailly & Maderson, 1984) and in crocodilians (ALibardi L, Thompson MD, 2001), and of avian scuta, feathers or hairs: only in the latter three is a placode individualized, followed by the formation of a dermal papilla. (DF) The usual expression of En-1 in the epidermis of the plantar region prevents the formation of beta-keratinized (-ker) cutaneous appendages (D,D), while the association of a plantar dermis with a tarsometatarsal epidermis leads to the formation of small scuta (E,E) and that with a neutral epidermis from the midventral apterium leads to feather morphogenesis (F,F). The curls on your head may have originally served as an evolutionary advantage for growing bigger human brains, according to new research that involved . The appearance of those two structures is linked to the initiation and the long phase of outgrowth especially of feathers and hairs, which both depend on a high expression of the Wnt canonical pathway. Development and evolution of the amniote integument: current landscape and future horizon. Sawyer RH. The roots of mammalian hair go far back into evolutionary history, according to a new study. Scales, Feathers and Hair Have a Common Ancestor 2003. However, the alleged primitive protofeathers formed of filamentous structures may, at least in some cases, have been misinterpreted, and correspond in fact to degraded collagen fibers, as in the early theropod dinosaur Sinosauropteryx (Lingham-Soliar et al. One theory displayed in "The evolution of mammalian keratinized structures" (abstract only) is that mammalian hair developed along the following pathway: So this paper would suggest that hair production evolved separately from but parallel to the movement away from reptilian scales. Andl T, Reddy ST, Gaddapara T, Millar SE. Better to call them protomammals, as they were more closely related to mammals than any reptile. In the chick, three main types of scales can be distinguished: large, oblong overlapping scales, or scuta, cover the dorsal surface of the tarsometatarsus and digits; smaller oblong overlapping scales, or scutella, cover the ventral face of the tarsometatarsus; and small, rounded, non-overlapping scales, or reticula, cover the plantar surface (Lucas & Stettenheim, 1972). Please be respectful of copyright. I would like to thank previous PhD students and postdoctoral fellows, whose experimental results led to the current hypothesis: Sandrine Blanchet-Rhtore, Rachida Cadi, Catherine Chaloin-Dufau, Pascale Delorme-Tacnet, Corinne Ferraris, Ingrid Fliniaux, Benoit Kanzler, Jean-Jacques Michaille, Frederic Michon, Isabel Olivera-Martinez, Sylvain Missier, David J. Pearton, Fabrice Prin, Jacques Thlu, Jean Viallet, and Ying Yang. 2000) and the skin is endowed with regional characteristics, as revealed by the experience with FGF2 beads (Fig. It appears that over a short period of a million years (well short it terms of evolution), fur spontaneously appearedfirst in patches on the face of the early mammals and eventually covering their whole bodies. Basically, pseudoscales. Thus they arise from the part of science that I know best: the embryogenesis of the integument of common day amniotes. Gat U, DasGupta R, Degenstein L, Fuchs E. De novo hair follicle morphogenesis and hair tumors in mice expressing a truncated -catenin in skin. Reproduced with permission of the Company of Biologists. All Rights Reserved. But a study. 1997) or by Shh signaling inhibition (Prin & Dhouailly, 2004). In all living vertebrates, at least from trout to human, specific types of alpha-keratins, K1-2/K10 and K3/K12, characterize the epidermis and corneal epithelium, respectively, showing a strong homology in the different lineages (OGuin et al. As their adhesiveness wanes, the stem cells escape from their location, called the bulge, into the dermis. Today, our mission remains the same: to empower people to evaluate the news and the world around them. Moreover, it may be a link between the Hox code in the hindlimb and the down-regulation of the beta-catenin in this region. Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. 2B) may contribute to the hypothesis that the feet of the ancestors of common day birds were almost entirely covered with feathers. Velmaat JM, Mailleux AA, Thiery JP, Bellusci S. Mouse embryonic mammogenesis as a model for the molecular regulation of pattern formation. 1987; Chaloin-Dufau et al. Can I use Sparkfun Schematic/Layout in my design? A cast of the skull of Estemmenosuchus, a synapsid that may have had smooth skin, at the Arizona Museum of Natural History. 1990), which give rise to successive hair generations. Widelitz RB, Jiang T-X, Lu J, Chuong C-M. BETA-catenin in epithelial morphogenesis: conversion of part of avian foot scales into feather buds with a mutated beta-catenin. All rights reserved. The other ectoderm derivatives, scales in birds, glands in mammals, and cornea in both lineages, appear to require a negative regulatory mechanism of this basic genetic program. Modulation of BMP signaling by Noggin is required for induction of the secondary (non tylotrich) hair follicle. Why Mammal Body Hair Is An Evolutionary Enigma Within a week, the first hair pegs are visible as projections into the mouse dermis of basal rabbit cells, which no longer express Pax6 and keratins K12/K3 (Fig. Epidermal glands in squamate: fine structure of pre-cloacal glands in Amphisbaena alba (Amphisbaenia, Amphis baenidae). The content is provided for information purposes only. Vol. 5D,D) (Nhri et al. 1998; Widelitz et al. 2008. 1 Answer. 2008). After Fliniaux et al. Pangolin scales are certainly not retained from fish. 2003; Pearton et al. Bereiter-Hahn J, Matolsty AG, Sylvia Richards K. Biology of the Integument Vol 2. 19, 1: 1-26. First thing in the morning, my mind is on autopilot. The latter possess placodes associated with dermal condensations (Sire et al. 2000; Prin & Dhouailly, 2004). There's no indication that hair evolved more than once, so fur has to be at least that old. Chuong C-M, Wu P, Zhang FC, et al. Where did hair and feathers originate from? Can a mammal grow feathers Epidermal keratinization in the salamander and a comparison with other amphibia. In contrast, the dermis of the chick plantar region is able to trigger a complete feather morphogenesis in an apteric epidermis, the later being endowed with an intact cutaneous appendage program (Prin et al. The extension of these micro-limbs into hairs was selected towards as a result of their thermally insulating effect by-product rather than for their sensory role, however. The expression of Shh, which is at a low level at the distal tip of the scuta, is up-regulated in two or three spots (arrowheads) of the scuta distal tip. What made megalodon such a terrifying predator? As late reptiles and early mammals developed whiskers and a better sense of hearing, their brains had to process more information. In mice, the expression of En-1 in the presumptive palmar/plantar ectoderm is required for eccrine gland development (Loomis et al. The role of epithelial-mesenchymal interactions in regulating gene expression during avian scale morphogenesis. Every print subscription comes with full digital access. Lemurs in colder regions are more likely to have dark hair. After Prin & Dhouailly, 2004. the diffusible proteins that remains similar, but the building of the sentences. The recent discovery of many intermediate forms of theropods and even of non-theropod dinosaurs exhibiting feather-like appendages in the Liaoning province of China has introduced new insights into the evolution of feathers (Brush, 2000; Prum & Williamson, 2001; Chuong & Homberger, 2003; Hou et al. Mammals have hair. However, the evolution of wild primate hair remained relatively understudied until recently. Such a redistribution is enhanced by BMP7 and FGF4 from the placodal epidermis and arrested by BMP2 (Michon et al. an epidermis adorned with a variety of alpha-keratinized bumps, and thus may have presented similarities with the integument of common day terrestrial amphibians. Our primary results showed that in mammals, the embryonic (Ferraris et al. After 1 week, the beta-catenin-expressing cells form hair plugs (C). Did Indiana Jones help or hurt archaeology? In crocodilian lineage, the dermal condensation appears after scale morphogenesis, and is diverted to osteoderm formation. With this theory, I suggest that the alpha-keratinized hairs from living synapsids may have evolved from the hypothetical glandular integument of the first amniotes, which may have presented similarities with common day terrestrial amphibians. Anonymous sites used to attack researchers. Image from Kielan-Jaworowska and Hurum, 2006. Dhouailly D. Specification of feather and scale patterns. Tzika, Di-Po, Milinkovitch UNIGE 2016, Reptile embryos, they discovered, develop tiny structures that possess all the morphological and molecular characteristics of anatomical placodes just like with birds and mammals. (D) After Widelitz et al. Associating external integument to internal scaffold is no simple task. Thus in my view, avian ectoderm and mammalian ectoderm are genetically programmed to build feathers or hairs, respectively. Nature 416: 816822. To find out, Nicolas Di-Po and Michel Milinkovitch at the University of Geneva in Switzerland studied skin development in embryos of Nile crocodiles (Crocodylus niloticus; pictured right), corn snakes (Pantherophis guttatus) and bearded dragons (Pogona vitticeps). This, suggest that keratin genes "are not restricted to mammals and suggest that the evolution of mammalian hair involved the co-option of pre-existing structural proteins." Reproduced with permission of the Company of Biologists. It can be postulated that an absence of the beta-catenin pathway activation can lead to the formation of interfollicular skin, i.e. Botchkarev V, Paus R. Molecular biology of hair morphogenesis: Development and cycling. The feather is the most complex cutaneous appendage yet to be produced during evolution. Epithelial-Mesenchymal Interactions in Development. 1998) and embryo (Nhri et al. Anterior segment development relevant to glaucoma. googletag.cmd.push(function() { googletag.display('div-gpt-ad-1449240174198-2'); }); Researchers in the Primate Genomics Lab at the George Washington University examined what factors drive hair variation in a wild population of lemurs known as Indriidae. Apart from any fair dealing for the purpose of private study or research, no Ferraris C, Chevalier G, Favier B, Jahoda CA, Dhouailly D. Adult corneal epithelium basal cells possess the capacity to activate epidermal, pilosebaceous and sweat gland genetic programs in response to embryonic dermal stimuli. Feathers, hair, and scales: Do they share a common ancestry? In reverse, the mammary gland apparently derives from an ancestral sweat or sebaceous gland that was associated with hair follicles, an association which is retained in living monotremes, and transiently in living marsupials. Previously, biologists had considered the possibility that hair evolved from scales or feathers, but the paucity of fossils showing the evolution from reptiles to . The origin and evolution of mammary glands. (D) Production of a skin with a pluristratified epidermis and three stage 3 hair pegs by a graft under the kidney capsule of mouse amnion associated to a mixed clump of Noggin- and Shh-producing cells. Another main difference between the skin and the cornea, in addition to the transparency of the latter, is the formation by the skin of cutaneous appendages, which are exclusively composed of epidermal cells and depend to a large extent upon dermal influences (Dhouailly, 1977; Chuong, 1998; Millar, 2002). Jean-Yves Sire and Matt Vickarious who organized the symposium on Vertebrate Integument in Paris. Get the most important science stories of the day, free in your inbox. 2004; Nhri et al. Ultrastructural observations on the embryonic development of the integument of Lacerta muralis (Lacertilia, Reptilia). Then I will outline how a shared similar stage of placode formation is reached in the formation of avian scales, feathers, and hairs, with the exception of reptilian scales. Drawing from brain endocasts created from CT scans of the 200-195 million year old mammals Morganucodon and Hadrocodium, Rowe and colleagues were able to track how mammal brains evolved. Medical research advances and health news, The latest engineering, electronics and technology advances, The most comprehensive sci-tech news coverage on the web. Engrailed-1 and the inhibition of cutaneous appendage morphogenesis in the chick foot. Finally, reticula are not true cutaneous appendages, and appear to be feathers arrested in the initiation step of their morphogenesis: formation of a slight bump, without a placode. In a variety of living amphibians, such as toads, a stratum corneum-like layer exists, but it is only one to three cell depths, and nuclear remnants still persist (Spearman, 2005). The amnion, which characterizes the amniotes, has a simple structure: a unistratified ectoderm overlying a unicellular stratum of somatopleural fibroblasts. When did hair first evolve? However, the fossil data for intermediate forms of these three so-called skin appendages have been lacking. In: Morris-Kay G, editor. 2000) did not obtain reticula-feather metaplasia, only scuta-feather metaplasia. Your feedback is important to us. It depends on an early induction by the neuroderm, followed by a negative regulation (our unpublished data). Spearman RIC. But it turns out that fur, feathers, and scales all evolved from one common ancestor, no matter how different these . This document is subject to copyright. 3B,D). The Evolution of Fur and Mammals | VirtEvo DevBlog & Speculative Biology
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