阿根廷圣胡安自然科学博物馆研究员奥斯卡·艾科波16日表示，科学家已经在阿根廷发现杂食恐龙的化石，这是食草恐龙向食肉恐龙过渡环节中缺失的一环。
这座博物馆位于阿根廷首府布宜诺斯艾利斯西部大约1200公里处，该馆馆长艾科波说：“它是一种杂食性恐龙，换句话说就是，植物和肉类它都吃，杂食性恐龙是食肉恐龙和巨型四足食草恐龙之间缺失的一环。这是揭开恐龙起源的一个非常重要的谜底。”
艾科波和该博物馆古生物部主管里卡多·马丁兹3年前在圣胡安月亮谷公园发现杂食恐龙化石。16日他们将研究结果发表在在线杂志《公共科学图书馆—综合》上。
由于20世纪80年代科学家在阿根廷发现内乌肯阿根廷龙(Neuquen of the Argentinosaurus Huinculensis)等恐龙化石，该国已经获得侏罗纪公园的荣誉称号。阿根廷龙是目前已知的最大的食草恐龙，体长超过40米。
1993年底，科学家在阿根廷发现卡洛琳南方巨兽龙(Giganotosaurus carolinii)的化石，这种恐龙是目前已知体积最大的食肉恐龙，也是当前化石领域仍在探索的一种恐龙。（生物谷Bioon.com）
生物谷推荐原始出处：
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.
