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Texas Fossil Identified As the World's Oldest Known Bird

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Texas Fossil Identified As the World's Oldest Known Bird Texas Fossil Identified as the World's Oldest Known Bird Professor Sankor Chatterjee is a palaeontologist working at the Texas Tech University in the USA. He has recently reported the remarkable discovery in a Texas quarry of a new species of fossil 'protobird' which predates by at least 75 million years the well-known Archaeopteryx litho­ graphica. The discovery gives new insight into the origin and early radiation of birds, their link to early dinosaurs, and the tempo and mode of bird evolution. The following is extracted from a News Release by the Royal Society, London for the information of our members-Ed. Until now Archaeopteryx has generally been considered to be the oldest known l>ird and, since its discovery in 1963, it has been the subject of lively scientific debate ..about the evolutionary link between reptiles and birds and the development of flight. -The latest fossils of two skeletons found side by side in the Late Triassic (about 225 mi1tion years old) Dockum Formation of Texas show that there existed in this -earlier period a predatory protobird that, when full grown and counting its long bony tail, was about the size of a pheasant. Yet, the animal displayed many .advanced avian features that place it closer to the ancestry of modern birds than -----~~~, ... 90 WORLD'S OLDEST KNOWN BIRD Archaeopteryx. The new find pushes Archaeopteryx to a side branch of bird' genealogy, making it a 'living fossil' in the Jurassic: world. The new fossil has been named Protoavis texensis meaning 'first bird from Texas'. Resembling a small, meat· eating or theropod dinosaur in the rear,. Protoavis reveals its true identity in the front portions of the skeleton. The long bony tail and hind legs are like those of a theropod, indicating their dinosaurian heritage; but the skull, neck bones, fore limbs, shoulder and hip girdles are un­ mistakably bird-1ike. The morphology of the flight apparatus indicates that Proto­ avis could fly well and had acquired flapping flight. It has a 'wish bone' like­ modern birds that acted as a spring between two shoulder girdles during flight. The neck of Protoavis is also typically avian. Only birds have neck vertebrae with. saddle·sbaped surfaces between them, providing for extreme flexibility in neck movement. Protoavis, unlike Archaeopteryx, has such neck bones. The hip bones were fused and streamlined for aerodynamic function. The animal had a large brain and large eyes with binocular vision; its refined hearing organ suggests that this. ancient bird communicated vocally. Neurosensory specializations may be associated with birdlike balance, coordination, flight, agility and high metabolic activity. Its­ skull and other bones were lightly built and its teeth were restricted to the tip of the jaws, the back teeth having been lost. The most crucial evidence in support of the avian identity of Protoavis lies at the rear part of the skull. Dinosaurs, like modern crocodiles, had two extra holes, in the temple behind the eye socket to accommodate muscle bulges. In both Protoavis and modern birds, on the other hand, these holes have merged with the' eye socket with the loss of bony bars between them. This architectural change­ makes the skull of Protoavis and birds highly flexible allowing the upper jaw t(} open wide for manipUlation of foods. Dinosaurs and Archaeopteryx were unable· to move the upper jaw, and their skulls were rigid. Althougb Pl'otoavis support the theory that theropods are the closest relatives. to birds, no evidence yet exists of theropods predating Protoavis that dispJay all features required of its immediate ancestry. Thus one of the major theories of evolution - that birds descended from small theropods - though highly attractivet has yet to be supported by fossil evidence. There is a growing opinion among evolutionary biologists that many groups of" organisms had evolved rapidly' in jumps' followed by a long period of stability-a model elaborated by Eldredge and Gould as 'punctuated equilibria'. The sudden appearance of avian novelties in Protoavis, which established the basic structure of birds, followed by a more gradual period of refinement and adaptation, illustrates. another example of punctuated evolution. The full text oj the paper is published (29 June 1991) in the Royal Society's Journal Philosophical Transactions (Series B) Vol. 332, pp. 277-346-Ed. .
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