Dinosaurs Evolve—and Fly 285(fig. 12.14A), it had the primitive sickle-like claws on the hind feet, the long bony tail, teeth,
and many other theropod features, but it also had birdlike features such as the fusion of its
lower back vertebrae with the pelvis (the synsacrum), holes in its vertebrae for all the blood
vessels and air sacs found in living birds, fingers with quill knobs, suggesting that it was
feathered and could fly (no surprise here), and the fibula (the smaller shin bone) that does
not reach the ankle. Birds have reduced the fibula to the tiny splint of bone that you bite into
when you are eating a chicken or turkey drumstick, but Archaeopteryx has a fully developed
fibula like that of dinosaurs.
The next step is marked by Confuciusornis and its relatives (fig. 12.14B), which has
a unique feature found in all higher birds: the pygostyle, formed by the fusion of all the
old dinosaurian tail vertebrae into a single “parson’s nose.” These higher birds have also
increased the number of lower back vertebrae fused to the synsacrum and elongated the
FIGURE 12.13. The evolution of feather types from simple pinshafts to down plumes to complex flight feathers
with asymmetric vanes and shaft. On the basis of their appearance in various feathered nonflying dinosaurs
from Liaoning, we can demonstrate that most predatory dinosaurs (including T. rex) probably had feathers of
some sort. (Modified from Prum and Brush 2003)
AllosaurusTyrannosaurusTetanuraeCoelurosauriaAvialaeArchaeopteryxLiving birdsDromaeosaurusMicroraptorSinornithosaurusTroodonOviraptorCaudipteryxOmithomimidsTherizinosaursAlvarezesauridsSinosauropteryxCompsognathusType 5Type 4Type 1Type 2-3