pygostyle

[ pahy-guh-stahyl ]

/ ˈpaɪ gəˌstaɪl /

the bone at the posterior end of the spinal column in birds, formed by the fusion of several caudal vertebrae.

Origin of pygostyle

1870–75; < Greek pȳgo- (combining form representing pȳgḗ rump) + stŷlos pillar

py·go·styled, adjective py·go·sty·lous, adjective

The posterior caudal vertebrae are not united together to form a pygostyle.

The Vertebrate Skeleton |Sidney H. Reynolds
The tail is short and the posterior caudal vertebrae are generally ankylosed together forming a pygostyle.

The Vertebrate Skeleton |Sidney H. Reynolds
The pars caudifemoralis is flat, somewhat spindle-shaped, and passes anteroventrally from the pygostyle to the femur.

Myology and Serology of the Avian Family Fringillidae |William B. Stallcup
The last six or seven caudal vertebrae coalesce into the pygostyle, an upright blade which carries the rectrices.

Encyclopaedia Britannica, 11th Edition, Volume 3, Slice 7 |Various

In proportionate size (see Table 7), the pygostyle of Bombycilla is the smallest in the family.

Phylogeny of the Waxwings and Allied Birds |M. Dale Arvey