北京時間2月15日消息，據(jù)國外媒體報道,，眾所周知,，蝙蝠一直依靠反射超聲波來確定方位。但美國的科學家們近日稱,，通過分析出土的蝙蝠化石,，科學家們發(fā)現(xiàn)5000多萬年前的蝙蝠并不像目前的蝙蝠那樣擁有聲波定位系統(tǒng)。
在2月14日出版的《自然》（Nature）雜志上,，美國的科學家公布了他們的這一最新發(fā)現(xiàn),。美國科學家稱，他們最近在美國懷俄明州出土了一個目前已知最原始的蝙蝠的骨架化石,，這個近乎完整的骨架化石可以追溯至始新世紀初,，即大約5250萬年以前。頭骨的形狀表明,，早期蝙蝠擁有功能強大的翅膀,，卻無法像現(xiàn)代蝙蝠一樣憑回波測定方位，即通過發(fā)送聲波和分析回聲來確定距離和方向,。美國自然歷史博物館的進化生物學家南希·西蒙斯說：“這個發(fā)現(xiàn)令我們大吃一驚,，因為我一直習慣地認為始新世的蝙蝠都是能夠憑回波測定方位的,，突然發(fā)現(xiàn)一只不具備回波測向能力的蝙蝠的確令人興奮。”
此次發(fā)現(xiàn)的意義非同尋常,，因為它有助解答一個長期令人困惑的科學問題,。西蒙斯說：“這個發(fā)現(xiàn)真正令人激動的原因在于，它使我們有機會得以重新審視一個古老的問題——究竟是回波測定在先,，還是飛行在先,？一直以來，我們都無法準確回答這個問題?，F(xiàn)在我們找到了有力證據(jù),，證明飛行在先的假說,，就像此次發(fā)現(xiàn)的蝙蝠一樣，能夠飛行卻缺乏回波測定能力,。這樣一來,，這個一度困擾我們許久的科學問題就有了很好的答案。”這種早期蝙蝠名為Onychonycteris finneyi,，它們可能需要依賴視覺、嗅覺和平常的聽覺來進行飛行和搜尋獵物,。西蒙斯表示,，這是蝙蝠家族的一個新分支,，它不屬于之前我們已知的任何蝙蝠家族,。
這只蝙蝠的四肢形狀表明，這種動物曾是一個敏捷靈活的攀緣者,，能夠爬樹并吊在樹枝上,。西蒙斯說：“與大部分蝙蝠相比，由于它的后腿成比例地長出許多,，因此它可能十分擅長攀爬和吊掛,。這意味著它可能是蝙蝠與其哺乳動物祖先之間的一個橋接點。”盡管Onychonycteris finneyi是迄今為止發(fā)現(xiàn)的最原始的蝙蝠,，但卻不是最古老的,，它與名為Icaronycteris的蝙蝠生活在同一時代,，兩者化石的出土遺址也在同一地區(qū),。但是，Icaronycteris的化石卻表明它能夠利用回波測定來獵捕食物,。
在通常情況下,，蝙蝠大腦的不同部分能夠截獲回聲信號的不同成分,。蝙蝠大腦中的某些神經(jīng)元對回聲頻率非常敏感，而另一些則對二個連續(xù)聲音之間的時間間隔極為敏感,。大腦各部分的共同協(xié)作使蝙蝠作出對反射物體性狀的判斷,。蝙蝠用回聲定位來捕捉昆蟲的靈活性和準確性，是非常驚人的,。據(jù)統(tǒng)計,，蝙蝠在幾秒鐘內就能捕捉到一只昆蟲，同時,，他們還具有驚人的抗干擾能力,，能從雜亂無章的充滿噪聲的回聲中檢測出某一特殊的聲音，然后很快地分析和辨別這種聲音,，以區(qū)別反射音波的物體是昆蟲還是石塊,，或者更精確地決定是可食昆蟲，還是不可食昆蟲,。（來源：新浪科技 劉妍）
（《自然》（Nature）,，451, 818-821，14 February 2008,，Nancy B. Simmons,，Gregg F. Gunnell）
生物谷推薦原始出處：
Nature 451, 818-821 (14 February 2008) | doi:10.1038/nature06549; Received 21 September 2007; Accepted 10 December 2007
Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation
Nancy B. Simmons1, Kevin L. Seymour2, Jörg Habersetzer3 & Gregg F. Gunnell4
American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024, USA
Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada
Forschungsinstitut Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany
Museum of Paleontology, University of Michigan, Ann Arbor, Michigan 48109-1079, USA
Correspondence to: Nancy B. Simmons1 Correspondence and requests for materials should be addressed to N.S. (Email: [email protected]).
Abstract
Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species1. Although recent studies unambiguously support bat monophyly2, 3, 4 and consensus is rapidly emerging about evolutionary relationships among extant lineages5, 6, 7, 8, the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood5, 7, 8, 9. Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non-flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a 'flight first' hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding–fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under-branch hanging behaviour.
