Diferenzas entre revisións de «Pelaxe»

 
== Composición ==
<!--
[[File:Down Awn and guard hairs of cat 2012 11 13 9203r.JPG|thumb|Down, awn and guard hairs of a domestic tabby cat]]
Fur usually consists of two main layers:
*Down hair (known also as undercoat or ground hair) — the bottom layer consisting of wool hairs, usually wavy or curly without straight portions or sharp points; down hairs tend to be shorter, flat, curly, and more numerous than the top layer. Its principal function is [[thermoregulation]]; it maintains a layer of dry air next to the skin and repels water, thus providing thermal insulation.
*Guard hair — the top layer consisting of longer, generally coarser, nearly straight shafts of hair that protrude through the down hair layer. The [[Anatomical terms of location|distal]] ends of the guard hairs provide the externally visible layer of the coat of most mammals with well-developed fur. This layer of the coat displays the most marked [[pigmentation]] and gloss, including coat patterns adapted to display or [[camouflage]]. It is also adapted to shedding water and blocking sunlight, protecting the undercoat and skin from external factors such as rain and [[ultraviolet]] radiation. Many animals, such as domestic cats, erect their guard hairs as part of their [[threat display]] when agitated.
 
[[FileFicheiro:Down Awn and guard hairs of cat 2012 11 13 9203r.JPG|thumbminiatura|Down,Tipos awnde andpelo guardque hairs offorman a domesticpelame tabbydun catgato doméstico.]]
Mammals with well-developed down and guard hairs also usually have large numbers of [[awn hair]]s. These begin their growth much as guard hairs do, but change their mode of growth, usually when less than half the length of the hair has emerged. This portion of the hair is called awn. The rest of the growth is thin and wavy, much like down hair. In many species of mammals, the awn hairs comprise the bulk of the visible coat. The [[Anatomical terms of location|proximal]] part of the awn hair shares the function of the down hairs, whereas the [[Anatomical terms of location|distal]] part aids the water-shedding function of the guard hairs, though their thin basal portion prevents their being erected like true guard hairs.
A pelame dos animais xeralmente consta de dúas capas principais de pelo con distintas características, que son:
[[File:Wet Fur - CGI.jpg|thumb|Computer-generated wet fur]]
*Pelo da capa inferior de tipo peluxe. A capa inferior consta de pelos lanosos, xeralmente ondulados ou rizados sen porcións rectas nin puntas bicudas; adoitan ser pelos curtos, planos, rizados e máis numerosos que os da capa superior. A súa principal función é a [[termorregulación]]; manteñen unha capa de aire seco a rentes da pel e repelen a auga, o que proporciona o illamento térmico.
*Pelos da capa superior ou de cobertura. A capa superior constaq de pelos máis longos, xeralmente máis bastos, con talos case rectos, que fan protrusión entre os pelos da capa inferior. Os extremos distais destes pelos orixinan a capa visible externamente da pelame da maioría dos animais con pelame ben desenvolvida. Esta capa mostra a [[pigmento biolóxico|pigmentación]] e brillo máis marcado, incluíndo os patróns de debuxo e coloración adaptados para a exhibición ou a [[camuflaxe]]. Tamén está adaptada a protexer da auga e bloquear a luz solar, protexenco así a capa inferior e a pel de factores externos como a chuvia e a [[luz ultravioleta]]. Moitos animais, como os gatos domésticos, poden ourizar os pelos desta capa comoparte da súa exhibición de ameaza cando son inquietados.
 
Os mamíferos con capas inferior e superior de pelo ben desenvolvidas tamén adoitan ter un gran número de pelos intermedios. Estes empezan o seu crecemento de forma similar aos pelos típicos da capa superior, pero cambian o seu modo de crcemento, xeralmente cando emerxeu menos da metade da lonxitude do pelo. O resto do crecemento é formando un pelo delgado e ondulado, similar ao pelo da capa inferior. En moitas especies de mamíferos, estes pelos comprenden a maior parte da súa pelame visible. A parte proximal destes pelos ten a mesma función que os pelos da capa inferior, mentres que a parte distal achega a función de protección contra a auga que teñen os pelos a capa superior, aínd que a súa porción basal delgada impide que poidan ser ourizados como os verdadeiros pelos da capa superior.
The modern fur arrangement is known to have occurred as far back as [[Docodonta|docodonts]], [[haramiyida]]ns and [[Eutriconodonta|eutriconodonts]], with ''[[Castorocauda]]'', ''[[Megaconus]]'' and ''[[Spinolestes]]'' preserving compound follicles with guard hair and underfur.
[[Ficheiro:Wet Fur - CGI.jpg|miniatura|Pelame de auga xerada por computador.]]
 
As características modernas da pelaxe dos mamíferos crese que apareceron cos [[Docodonta|docodontos]], [[haramiyidano]]s e [[Eutriconodonta|eutriconodontos]], e os fósiles de ''[[Castorocauda]]'', ''[[Megaconus]]'' e ''[[Spinolestes]]'' conservaron folículos compostos con pelos das dúas capas.
==Mammals without fur==
Hair is one of the defining characteristics of mammals, however, several species or breeds have considerably reduced amounts of fur. These are often called "naked" or "hairless".
 
== Mamíferos sen pelo ==
===Natural selection===
O pelo é unha das características definitorias dos mamíferos, pero varios grupos, especies ou razas teñen unha cantidade de pelo considerablemente reducida ou case ausente, polo que se denominan "espidos" ou "sen pelo".
 
=== Selección natural ===
<!--
Some mammals naturally have reduced amounts of fur. Some [[semiaquatic]] or [[aquatic animal|aquatic]] mammals such as [[cetacean]]s, [[pinniped]]s and [[hippopotamuses]] have evolved hairlessness, presumably to reduce resistance through water. The [[naked mole-rat]] has evolved hairlessness, perhaps as an adaptation to their subterranean life-style. Two of the largest extant mammals, the [[elephant]] and the [[rhinoceros]], are largely hairless. The [[hairless bat]] is mostly hairless but does have short bristly hairs around its neck, on its front toes, and around the throat sac, along with fine hairs on the head and tail membrane. Most hairless animals cannot go in the sun for long periods of time, or stay in the cold for too long. <ref name=ADW>{{cite web|last=Thomson|first=Paul|title=Cheiromeles torquatus|url=http://animaldiversity.ummz.umich.edu/accounts/Cheiromeles_torquatus/|publisher=Animal Diversity Web|accessdate=29 October 2013|year=2002}}</ref>
 
According to Statistics Canada, 2.6 million fur-bearing animals raised on farms were killed in 2010. Another 700,000 were killed for fur by traps.<ref>[http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/prim46a-eng.htm "Fur production, by province and territory"].</ref><ref>[http://www.peta.org/issues/animals-used-for-clothing/fur/ The fur industry]. Peta, n.d.</ref>
-->
 
== Notas ==
{{Listaref|33em}}
192.021

edicións