Evolution, 4th Edition

416 CHAPTER 16

Finally, there are feathers. Since 1996, researchers have described an astonish-

ing variety of feathered dinosaurs from China (FIGURE 16.15). In some species, the

feathers are filaments that coat the body, and likely provided insulation and were

used for display rather than flight. At least two extraordinary four-winged dino-

saurs, Microraptor gui and Anchiornis huxleyi, had long feathers on all four limbs.

Feathers may have characterized the entire theropod clade (perhaps even Ty ra nn o-

saurus). All these and many other features have enabled paleontologists to propose

phylogenetic relationships among dinosaurs, including the birds.

How do We Use Phylogenies?

The most basic reason for wanting to know how species are related is simply that

a phylogeny shows the family tree of life on Earth. But there are many other moti-

vations as well. In the following sections you will see how phylogenies are used

to date events in the evolutionary past, to study how genes (and even human cul-

tures) have evolved, to study adaptation, and to classify groups of species.

Dating evolutionary events

An important use of phylogenies is that they can tell us when some evolution-

ary changes happened—if DNA sequence differences among organisms or genes

more or less conform to a molecular clock. We introduced this idea in Chapter 2,

and saw in Chapter 7 why genetic differences between two species can accumu-

late at a roughly constant rate.

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_16.15.ai Date 11-02-2016

(A) Archaeopteryx (B) Microraptor (C) Anchiornis

FIGURE 16.15 Close relatives of birds among the feathered

dinosaurs. (A) The famous specimen of Archaeopteryx litho-

graphica, showing the wing feathers and the long bony tail with

feathers on both sides (150 Mya). (B) Microraptor gui was a four-

winged dromaeosaur, closely related to Velociraptor, that had

long feathers at the back of both the forelimbs and hindlimbs

(120–110 Mya). (C) Anchiornis huxleyi, from about 155 Mya. The

colors in the painting of Archaeopteryx are drawn from the art-

ist’s imagination, but the colors shown in the reconstructions of

Microraptor and Anchiornis are based on analysis of pigment-

containing organelles in the fossilized feathers. (B, fossil photo

© Mick Ellison, American Museum of Natural History.)

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