Ultimately, the pygostyle was amputated as well; therefore, this surgical procedure could also be considered a distal tail amputation.
Resolution of an undifferentiated pygostyle squamous cell carcinoma by tail amputation.
(a) The vessels entering the inferior umbilicus were coagulated and the attachments severed, (b) The first rectrix on each side was firmly attached to the pygostyle, which also extends to the very tip of the tail, making closure difficult.
(2) Isolation of the fan on the pygostyle effectively decouples the fanning mechanism from other tail movements.
The disparity between Archaeopteryx and modern birds is relatively large, yet can be attributed to three processes: shortening of caudal centra, sequestering of proximal caudals into the synsacrum, and fusing of distal caudals to form a pygostyle. These changes produced a functional tail skeleton of diminutive size, with only a minor reduction in the total number of caudal segments ([ILLUSTRATION FOR FIGURE 5 OMITTED]; Marshall 1872; van Oort 1904; Steiner 1938).
Although the early radiation of birds is still poorly known, forms such as Sinornis (Sereno and Rao 1992) and Iberomesornis (Sanz and Bonaparte 1992) had much shorter tail skeletons with a pygostyle. Thus, as with the wing, subsequent evolution of the caudal module included refinements for tail fanning (Gatesy and Dial, in press) and improved control.
In Early Cretaceous birds such as Sinornis and Iberomesornis, wing modifications indicative of advanced flight function are accompanied by a shortened tail skeleton and pygostyle (Sanz and Bonaparte 1992; Sereno and Rao 1992).
(py), part of the tail, is at end of vertebrate column.