Evolución paralela: Diferenzas entre revisións

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Miguelferig (conversa | contribucións)
Miguelferig (conversa | contribucións)
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==== Evolución paralela entre marsupiais e placentarios ====
Un dos exemplos máis espectaculares de evolución paralela proporciónano as dúas pólas principais en que se dividiron os [[mamífero]]s, os [[placentario]]s e os [[marsupiais]], que seguiron vías evolutivas independentes ao separánrense as masas de terra do antigocontinente de [[Gondwana]] hai uns 100 millóns de anos. En [[Neotrópico|Suramérica]], os marsupiais e os placentarios compartiron o ecosistema (antes da conexión entre América do Norte e do Sur); en [[Australia (continente)|Australia]], os marsupiais prevaleceron; e no Vello Mundo os placentarios foron os vencedores. Anteriormente, en todos eses lugares os mamíferos eran pequenos e ocupapan postos limitados no ecosistema ata que se produciu a [[evento de extinción cretáceo-paleoxeno|extinción en masa dos dinosauros]] hai 60 millóns e anos. Nese momento, os mamíferos das tres masas de terra empezaron a presentar unha maior variedade de formas e papeis no ecosistema. Aínda que algunhas formas eran íunicas de cada ambiente, a miúdo xurdiron tamén animais sorprendentemente similares en dous ou nos tres dos continentes separados. Exemplos destes son [[Litopterna|litopternos]] e [[cabalo]]s, cuxas patas son difíciles de distinguir; os tigres dentees de sabre europeos ([[Machairodontinae]]) e o marsupial dentes de sabre suramericano ''([[Thylacosmilus]])''; o [[lobo de Tasmania]] e o [[lobo]] europeo; e as [[toupa]]s placentarias e marsupiais, esquíos voadores e probablemente os ratos [[Antechinus]].
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One of the most spectacular examples of parallel evolution is provided by the two main branches of the [[mammal]]s, the [[placentals]] and [[marsupial]]s, which have followed independent evolutionary pathways following the break-up of land-masses such as [[Gondwanaland]] roughly 100 million years ago. In [[Neotropic|South America]], marsupials and placentals shared the ecosystem (prior to the [[Great American Interchange]]); in [[Australia (continent)|Australia]], marsupials prevailed; and in the Old World the placentals won out. However, in all these localities mammals were small and filled only limited places in the ecosystem until the [[Cretaceous–Paleogene extinction event|mass extinction of dinosaurs]] sixty-five million years ago. At this time, mammals on all three landmasses began to take on a much wider variety of forms and roles. While some forms were unique to each environment, surprisingly similar animals have often emerged in two or three of the separated continents. Examples of these include the [[Litopterna|litopterns]] and [[horse]]s, whose legs are difficult to distinguish; the European sabre-toothed cat ([[Machairodontinae]]) and the South American marsupial sabre-tooth ''([[Thylacosmilus]])''; the [[Tasmanian wolf]] and the European [[wolf]]; likewise marsupial and placental [[Marsupial mole|moles]], [[Sugar glider|flying squirrels]], and (arguably) [[Antechinus|mice]].
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== Notas ==