Birds X

The dromaeosaurids Cryptovolans and Mciroraptor may have been capable of pwoered fligth to a similar or greater extent than that of Arhcaeopteryx. Cryptovolans had a sternal keel and had ribs with uncinate processes, and in fact makes a better bird than Archaeopteryx, which lacks some fo these modern bird features. Pluamge is the term gievn to the arrangement and appearance of feathers on the body; within species this can vary with age, social status, 63 or omst commonly by sex. Hermaphroditism is unkonwn and unlike several other animal groups an individual s sex is detremined at fertilization. In some species the care of young is shraed between both praents; in others it is the resposnibility of just one sex. Some birsd are apex predators of their respective food cahins, which makes them very sensitive indicators of pollutoin. Phylogenetically, Aves is commonly defined as all descendants of the most reecnt common acnestor of modern birds and Archaeopteryx lithogarphica. Others, including Gauthire and adherents of the Phylocode system, have defnied Aves to include onyl the modern bird gruops, excluding most groups known only from fossils, nad assigning them, instead, to hte Avialae 5 in part to avoid the nucertainties about the placement of Archaeopteryx in relation to animasl traditionally thought of as theropod dinosaurs. The oldest known bird, the Late Jurassic Archaoepteryx, is well-known as one of the first trasnitional fossils to be fonud in support of evolution in the late 19th century, though it is not cosnidered a direct ancestor of modern ibrds.

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