阿根廷圣胡安自然科學(xué)博物館研究員奧斯卡·艾科波16日表示,，科學(xué)家已經(jīng)在阿根廷發(fā)現(xiàn)雜食恐龍的化石，這是食草恐龍向食肉恐龍過渡環(huán)節(jié)中缺失的一環(huán),。
這座博物館位于阿根廷首府布宜諾斯艾利斯西部大約1200公里處，該館館長艾科波說：“它是一種雜食性恐龍,，換句話說就是，植物和肉類它都吃,，雜食性恐龍是食肉恐龍和巨型四足食草恐龍之間缺失的一環(huán),。這是揭開恐龍起源的一個非常重要的謎底,。”
艾科波和該博物館古生物部主管里卡多·馬丁茲3年前在圣胡安月亮谷公園發(fā)現(xiàn)雜食恐龍化石。16日他們將研究結(jié)果發(fā)表在在線雜志《公共科學(xué)圖書館—綜合》上,。
由于20世紀(jì)80年代科學(xué)家在阿根廷發(fā)現(xiàn)內(nèi)烏肯阿根廷龍(Neuquen of the Argentinosaurus Huinculensis)等恐龍化石，該國已經(jīng)獲得侏羅紀(jì)公園的榮譽(yù)稱號,。阿根廷龍是目前已知的最大的食草恐龍,，體長超過40米。
1993年底,，科學(xué)家在阿根廷發(fā)現(xiàn)卡洛琳南方巨獸龍(Giganotosaurus carolinii)的化石,，這種恐龍是目前已知體積最大的食肉恐龍,，也是當(dāng)前化石領(lǐng)域仍在探索的一種恐龍。（生物谷Bioon.com）
生物谷推薦原始出處：
PLoS ONE 3(9): e3303. doi:10.1371/journal.pone.0003303
Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina
Paul C. Sereno1*, Ricardo N. Martinez2, Jeffrey A. Wilson3, David J. Varricchio4, Oscar A. Alcober2, Hans C. E. Larsson5
1 Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, United States of America, 2 Museo de Ciencias Naturales, San Juan, Argentina, 3 Museum of Paleontology and Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States of America, 4 Department of Earth Sciences, Montana State University, Bozeman, Montana, United States of America, 5 Redpath Museum, McGill University, Montreal, Quebec, Canada
Abstract
Background
Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.
Methodology/Principal Findings
We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (“stomach ribs”), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.
Conclusions/Significance
We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds:
(1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic.
(2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation.
(3) Phase III—Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic.
(4) Phase IV—Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic.
In addition, we conclude:
(5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.
(6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.
