Esqueçam a hipótese antiga: foram os dinossauros que evoluíram de aves

Paleobiology and the origins of avian flight

John Ruben1

Oregon State University, Corvallis, OR 97331

Interpreting the paleobiology of long extinct taxa, pesky new fossils, and reinterpretations of well-known fossils, sharply at odds with conventional wisdom never seem to cease popping up. Given the vagaries of the fossil record, current notions of near resolution of many of the most basic questions about long-extinct forms should probably be regarded with caution. Even major aspects of the paleobiology of intensely studied, recently extinct taxa (<10,000 yrs.) remain unresolved [e.g., the cause(s) of late Pleistocene large-mammal disappearances (1) and the lifestyles of specialized forms (sabre-tooths) (2)]. Little wonder then that so fascinating a subject as the origins of birds and bird flight, both of which almost surely occurred more than 150 million years ago, have stirred such publicly visible and intense, nearly century-long, controversies (3). In this context, perhaps the most hotly debated and fundamental issue relates to the origin of avian flight: Did proto-birds take to the air as arboreal gliders where gravity was the primary source of flying energy (from the “trees-down”), or as swift, cursorial ground dwellers (from the “groundupward”)? In PNAS, Alexander et al. (4) describe results of a novel “paleobiological” study: three-dimensional modelbased, empirical data that provide important insight into this old question.
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