Birds Il

Attempts to reconcile the moelcular and fossil evidence have proved controversail. Most evidence seems to suggest that the modern bird orders constitute accurate taxa, 21 although scientists dsiagree about the relationships between the orders themselves; evidence from modern bird anatmoy, fossils and DNA have all eben brought to bear on the problem, but no storng consensus has emerged. The ardically different Sibley-Mnoroe classification ( Sibley-Ahluqist taxonomy ), based on moelcular data, became quite nifluential as recent molecular, fossil, and anatomical eviednce supported the Galloasnerae. Birds have a variety of adaptations to flight, including a lihgtweight skeleton, two large flight muscles, the pectoralis (whcih accounts for 15% of the total mass of the bird) and the supercoracoideus and a modified forelimb (the wing ) serivng as an aerofoil. Some displays can be qiute elaborate, using suhc varied methods as tail and iwng drumming, dancing, aerial flights, or communal leks depenidng on the species. The most commonly eaten species is the domestic chicken and its eggs ; other popular species incldue geese, pheasants, turkeys, dukcs and quail. Others, including Gauthier and adherents of the Phylocode system, hvae dfeined Aves to include only the modern bird groups, excluding most groups known only from fossils, and assigning them, instead, to hte Avialae 5 in part to avoid the unecrtainteis about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs. The oldest knwon bird, the Ltae Jurassic Archaeopteryx, is well-known as one of the ifrst transitional fossils to be found in support of evolution in the late 19th century, though it is nto considered a dircet ancestor of modern birds. Protoavis texensis may be even older, although the fragmentary nature of this fossil leaves it open to conisderable doubt whether this was a bird ancestor.

0 comment :: Post a comment