一個生有4個翅膀的恐龍的泡沫塑料模型揭示了它如何在樹林中滑翔,。（圖片提供:David Alexander等，美國《國家科學院院刊》）
鳥類究竟是如何學會飛行的,？用生有4個翅膀的帶羽毛恐龍的泡沫塑料模型進行的首個飛行測試表明,，早期鳥類可能是以樹林間的滑行作為它們飛行生涯的開始。
有關(guān)鳥類飛行進化的爭論是古生物學中一個持續(xù)時間最長且最熱門的話題。最早的鳥類是從樹上向地面滑翔的樹棲生物,，還是因進化出了翅膀而逐漸喜歡長距離跳躍的兩足陸生動物,？研究人員對此一直沒有形成統(tǒng)一的認識。
最近幾年,，研究人員嘗試利用數(shù)學分析和計算機模擬來確定早期鳥類的飛行能力,。同時至少有一個研究團隊根據(jù)化石建立了一個物理模型，并用其進行了風洞試驗,。而利用一種不同的方法,，美國勞倫斯市堪薩斯大學的生物力學專家DavidAlexander與該校以及中國沈陽市東北大學的同事，重建了一個小盜龍的模型——這是一種因生有4個翅膀而聞名的恐龍,。小盜龍是恐爪龍——一種類似于鳥的恐龍——的一種,。
研究人員制作了一副骨架，并用一個黏土“身體”覆蓋住了“骨骼”,，之后又插上了由現(xiàn)代雉雞羽毛——它們能夠完美地匹配保存在化石上的印記——制作的翅膀,。研究人員利用這個有羽毛的重建小盜龍制作了一些聚氨酯泡沫模型。研究人員從不同的高度發(fā)射了這些模型,，并記錄了它們每次滑翔的距離,、速度以及角度。研究人員在1月25日的美國《國家科學院院刊》網(wǎng)絡(luò)版上報告說：“小盜龍是一架老練的‘滑翔機’,，但它如果想從一棵樹干滑行到另一棵樹干,，則還存在著一點點困難。”
自稱由于具有飛機模型知識背景而加入古生物學家研究團隊的Alexander表示,，他不知道還有其他任何研究團隊設(shè)法進行過恐龍飛行模型的研究,。北京市中國科學院古脊椎動物與古人類研究所的古生物學家周忠和認為，這種新的方法“可能是”確定滅絕動物的飛行能力的“最有效的途徑之一”,。他預(yù)計基于其他動物化石的類似試驗將有助于澄清鳥類飛行是如何起源的,。
美國奧斯汀市得克薩斯大學的古生物學家JuliaClarke也認為這些模型是有用的，但是它們必將受到有關(guān)解剖學認識的限制,。她說,，以小盜龍為例，“我不相信現(xiàn)實中的動物會呈現(xiàn)出一些它們在研究中所采用的姿態(tài)”,。Clarke同時認為,，研究團隊已經(jīng)超越了樹棲或陸生假設(shè)的分歧，轉(zhuǎn)而考慮一些差別更加細微的問題,，例如推動飛行的解剖學進化因素,。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS January 25, 2010, doi: 10.1073/pnas.0911852107
Model tests of gliding with different hindwing configurations in the four-winged dromaeosaurid Microraptor gui
David E. Alexandera,1, Enpu Gongb, Larry D. Martina,c, David A. Burnhamc, and Amanda R. Falkc,d
aDepartment of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045-7534;
bDepartment of Geology, Northeastern University, Shenyang, Liaoning 110004, China;
cDivision of Paleontology, Biodiversity Institute, University of Kansas, Lawrence, KS 66045-7561; and
dDepartment of Geology, University of Kansas, Lawrence, KS 66045-7613
Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requires the hindwing to have at least 20° of negative dihedral (anhedral), all configurations were quite stable gliders. Glide angles ranged from 3° to 21° with a mean estimated equilibrium angle of 13.7°, giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6 m·s?1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.
