科學(xué)家在認(rèn)真研究鳥類的運動和呼吸方式后,，聲稱這些長著羽毛的人類朋友并非起源于恐龍。
數(shù)十年來,，人們清楚鳥類的腿骨結(jié)構(gòu)使它們更適合用膝蓋奔跑。但是俄勒岡州立大學(xué)的研究人員發(fā)現(xiàn),，鳥類的腿骨結(jié)構(gòu)還阻止了它們的肺部伸縮,，從而使其更適于飛行。包括人類,、大象,、蜥蜴和暴龍等獸腳亞目恐龍(theropod dinosaurs)在內(nèi)的，在陸地上行走的任何一種其他動物,，都擁有可以移動的腿骨,。
這一發(fā)現(xiàn)或許將迫使古生物學(xué)家重新思考長期以來一直存在的想法：現(xiàn)代鳥類是遠(yuǎn)古肉食性恐龍的直系后裔,。美國研究員約翰·魯本教授說：“我們竟然不了解最基本的鳥類生物學(xué)問題，這令我們非常吃驚,。伶盜龍(Velociraptor)不僅在身體的某些部位長有羽毛,，而且還喜歡在日落后活動。鳥類可能是從另一種生物進(jìn)化而來的,，在大部分恐龍依然存在的時候,，鳥類的進(jìn)化過程已經(jīng)開始了。”羽毛,、翅膀和鳥類獨特的運動方式都是獨立進(jìn)化而來的,。
在1.45億年到6500萬年間的白堊紀(jì)時代，恐龍和鳥類雙雙繁盛發(fā)展,。一直被認(rèn)為是最古老的鳥類——始祖鳥生活在1.5億年前,，而恐龍先于它，早在2億年前就已經(jīng)出現(xiàn)了,。魯本說：“現(xiàn)在似乎已經(jīng)很清楚,，鳥類是單獨進(jìn)化而來的，并不是獸腳亞目恐龍的后裔,。”他們的研究結(jié)果發(fā)表在《形態(tài)學(xué)》雜志上,。（生物谷Bioon.com）
生物谷推薦原始出處：
Journal of Morphology DOI:10.1002/jmor.10752
Cardio-pulmonary anatomy in theropod dinosaurs: Implications from extant archosaurs
Devon E. Quick *, John A. Ruben
Department of Zoology, Oregon State University, Corvallis, Oregon 97331
ABSTRACT
Although crocodilian lung and cardiovascular organs are markedly less specialized than the avian heart and lung air-sac system, all living archosaurs possess four-chambered hearts and heterogeneously vascularized, faveolar lungs. In birds, normal lung function requires extensive, dorsally situated nonvascularized abdominal air-sacs ventilated by an expansive sternum and specially hinged costal ribs. The thin walled and voluminous abdominal air-sacs are supported laterally and caudally to prevent inward (paradoxical) collapse during generation of negative (inhalatory) pressure: the synsacrum, posteriorly directed, laterally open pubes and specialized femoral-thigh complex provide requisite support and largely prevent inhalatory collapse. In comparison, theropod dinosaurs probably lacked similarly enlarged abdominal air-sacs, and skeleto-muscular modifications consistent with their ventilation. In the absence of enlarged, functional abdominal air-sacs, theropods were unlikely to have possessed a specialized bird-like, air-sac lung. The likely absence of bird-like pulmonary function in theropods is inconsistent with suggestions of cardiovascular anatomy more sophisticated than that of modern crocodilians.
