pygostyle

thumb|right|Pigeon skeleton with "plowshare"-type pygostyle (number 17) thumb|right|Confuciusornis sanctus with "rod"-type pygostyle and the two central tail feathers Pygostyle (; from Ancient Greek [] 'tail, rump' and [] 'pillar, column') is a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main component of the uropygium, a structure colloquially known as the '''bishop's nose, parson's nose, pope's nose, or sultan's nose'. This is the fleshy protuberance visible at the posterior end of a bird (most commonly a chicken or turkey) that has been dressed for cooking. It has a swollen appearance because it also contains the uropygial gland that produces preen oil.

==Evolution== Pygostyles probably began to evolve very early in the Cretaceous period, perhaps 140 – 130 million years ago. The earliest known species to have evolved a pygostyle were members of the Confuciusornithidae. The structure provided an evolutionary advantage, as a completely mobile tail as found in species such as Archaeopteryx is detrimental to its use for flight control. Modern birds still develop longer caudal vertebrae in their embryonic state, which later fuse to form a pygostyle.