Archaeopteryx and the ancestry of living birds

We now turn to a truly important fossil: Archaeopteryx. The name was first applied to a feather impression, found in 1860 in finegrained deposits of carbonate mud of Late Jurassic age located in Solnhofen, Bavaria (southern Germany; Figure 10.3). A year later feather impressions and articulated bones were quarried from the same locality. The half-meter long fossil seemed chimeric, because it had

Table 10.2. Characters shared by maniraptorans and living birds

Maniraptoran theropods

Modern birds

Teeth (+)

Teeth (-)

Braincase slightly enlarged

Swollen braincase

Tail long, well-developed

Pygostyle (+ )

Hand three-fingered; I, II, & III

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

Legs:

1. Bipedal

1. Bipedal

2. Tarsometatarsus

Foot:

3. Claws

Hollow bones; some pneumatic

Pneumatic bones

Furcula (wishbone)

Furcula (wishbone)

Trunk not rigid:

1. Sternum small; flat

2. Pelvis unfused

4. Flying adaptions (—)

Rigidified trunk:

1. Carinate sternum

2. Synsacrum

4. Flying adaptations

Feathers (+)

Feathers (+)

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

"bird" feathers co-existing with "reptilian" features, such as a tail and hands with claws.3 Since those early days, a total of seven specimens (plus the feather) of Archaeopteryx have been discovered (Figure 10.4).

Figure 10.3. The first evidence for Jurassic-aged birds: the feather of Archaeopteryx lithographica, described in 1861, from the Solnhofen quarry in Bavaria (scale in centimeters).

Archaeopteryx is no longer mysterious, and cladistic analysis has shown that it beautifully bridges the gap between theropod dinosaurs and modern birds (Table 10.3). As we know from Chapters 1 and 3, this does not mean that it is the ancestor of modern birds, but only that it incorporates many of the features we'd expect to find in the actual ancestor.

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