from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The plate supporting the tail-feathers in birds, formed from fused vertebrae.
from the GNU version of the Collaborative International Dictionary of English
- n. The plate of bone which forms the posterior end of the vertebral column in most birds; the plowshare bone; the vomer. It is formed by the union of a number of the last caudal vertebræ, and supports the uropigium.
from The Century Dictionary and Cyclopedia
- n. In ornithology, the vomer or plowshare bone of a bird's tail, consisting of a number of caudal vertebraæ ankylosed together for the support of the tail-feathers, and possessed by nearly all birds.
Could you please distinguish between the pygostyle and the cloaca?
This is one of my papers: "A pygostyle from a non-avian Theropod."
The politically (and anatomically) correct term is pygostyle -- literally rump post -- for the structure of fused vertebra that anchors the turkey's magnificent tail feathers (rectrices) and also harbors the uropygial gland, source of preen oil, the yummy fat the bird uses to groom its plumage.
There may be a simple network of genes that regulate this one early decision to form a pygostyle from a tail, but there have been tens of millions of years of adaptation by other genes to the modern condition; we're dealing with a large network of interlinked genes here, and unraveling one step in development doesn't mean that subsequent steps are still competent to respond in the ancient pattern.
For instance, birds have lost the long bony tail of their ancestors, reducing it to a little stump called a pygostyle.