Lessons from history

It turns out that when we look at the features of birds, although unique among living vertebrates, many are old friends from our excursion through Theropoda (see Chapter 9). These features include:

• Hollow bones; (diagnostic of theropods).

• Pleurocoels and pneumatic foramina; both present in birds; also present in some other saurischians; see Chapters 8 and 9).

• Bipedality (found in all theropods).

• Distinctive foot (found in all theropods).

• Three-fingered hand (found in most theropods).

• Furcula (a diagnostic character of Coelurosauria).

• Large tibia; small fibula thinning toward the ankle (diagnostic character of eumaniraptoran theropods).

2. At the dinner table we call them the "wishbone."

Humerus

Supracoracoideus muscle

Pectoralis muscle

Tendon ofsupracoracoideus muscle

Coracoid

Humerus

Tendon ofsupracoracoideus muscle

Supracoracoideus muscle

Pectoralis muscle

Coracoid

Furcula (wishbone)

Furcula (wishbone)

Figure 10.2. The two major muscles for flight: the pectoralis and the supra coracoideus. The pectoralis is the muscle used in the downward (power) stroke, while the supracoracoideus is used in the recovery stroke.

• Large braincase and stereoscopic vision (found in eumaniraptoran theropods).

• Feathers (found in non-avian avialan theropods; see below).

The shared, diagnostic characters between birds and theropods leaves us with the inevitable conclusion that birds are theropod dinosaurs.

Table 10.2 summarizes these diagnostic characters, but it also highlights a different problem: while there are many features that birds and theropods share, it's still quite a jump from one to the other. How to bridge that gap?

Was this article helpful?

+1 0

Post a comment