Archaeopteryx as a bird

Archaeopteryx was immediately recognized as a fossil of the most primitive bird known. The feathers identified it as a bird, as indeed many other features, particularly the stance, legs and feet, were remarkably bird-like, and, together with living birds, Archaeopteryx forms a monophyletic Avialae (Figure 10.6). But where did Archaeopteryx come from?

Figure 10.5. A reconstruction of Archaeopteryx, surrounded by photographs taken from the actual specimens. (a) Skull, seen from right side, note teeth; (b) feather impressions showing vanes and shaft superbly preserved; (c) trunk region seen from left side, note gastralia; (d) foot (four-toed and clawed, with symmetry around digit III; digit I opposite digits II, III, and IV); (e) right hand and wrist with clawed digits (in ascending order, I, II, and III). Inset: drawing of left wrist, showing semi-lunate carpal (Ra, radius; Ul, ulna; Sc, semi-lunate carpal); (f) robust theropod furcula.

Table 10.3. Distribution of characters among maniraptoran theropods, Archaeopteryx, and modern birds

Maniraptoran theropods

Archaeopteryx

Modern birds

Teeth (+)

Teeth (+ )

Teeth (-)

Braincase slightly enlarged

Braincase slightly enlarged

Swollen braincase

Tail long, well-developed

Tail long, well-developed

Pygostyle (+)

Hand three-fingered; I, II, III

Hand three-fingered; I, II, & III

Carpometacarpus (+); fused digits I, II, III

Legs:

1. Bipedal

1. Bipedal

1. Bipedal

2. Tarsometatarsus

Foot:

3. Claws

Hollow bones

Hollow bones

Pneumatic bones

Furcula (wishbone)

Furcula (wishbone)

Furcula (wishbone)

Trunk not rigid

1. Sternum small; flat

2. Pelvis unfused

4. Flight adaptions (-)

Trunk not rigid

1. Sternum small; flat

2. Pelvis unfused

4. Partial flight adaptations

Rigidified trunk

1. Carinate sternum

2. Synsacrum

4. Flight adaptations

Feathers (+)

Feathers (+)

Feathers (+ )

The plus sign (+) indicates character present; the minus sign (-) indicates character absent.

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