Evolution, 4th Edition

For example, we noted at the start of this chapter that birds are dinosaurs:

they are included in a dinosaur clade called the theropods (see Figure 16.1). Many

derived characters unify the birds and other theropods, and they differ from those

of any other tetrapod vertebrates [27]. The foot of birds and other theropods has

the same structure: the fifth toe is absent and the first toe is rotated backward. The

fibula is reduced to a thin splint. The pubis has a wide end and is directed back-

ward. There are air sacs in some of the vertebrae, and the long bones are hollow.

The clavicles are fused, forming the furcula (“wishbone”). The hand has only three

digits. Among the theropods is the famous feathered dinosaur (or early bird), the

Jurassic Archaeopteryx. Like other extinct theropods, such as Deinonychus, Archae-

opteryx had teeth and a long tail. The hands of Deinonychus and Archaeopteryx were

almost identical (FIGURE 16.14).

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_16.14.ai Date 01-02-2017

Amphioxus

Lampreys

Sharks

Morphology DNA

Ray-nned shes

Coelacanths

Lungshes

Amphibians

Monotremes

Marsupials

Placental mammals

Turtles

Tuatara

Lizards

Snakes

Turtles

Crocodiles

Birds

FIGURE 16.13 Relationships among major

groups of living vertebrates, as estimated

from morphological characters (left) and from

DNA sequences (right). On the whole, these

two sources of information provide similar

estimates of the phylogeny. The relationships

of turtles were uncertain from morphologi-

cal data but have been determined from

genomic data. Among these taxa, the trees

based on the two sources of data differ only

with respect to the relationships of the turtles,

which are shown in different positions (in

blue) in the two trees. (After [7, 24, 34].)

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_16.14.ai Date 01-02-2017

Postosuchus Deinonychus Archaeopteryx Tinamou

FIGURE 16.14 Hand features shared by

theropods, including the extinct dinosaurs

and living birds. Shown are the left hand

of the dinosaur Deinonychus, the feath-

ered dinosaur Archaeopteryx, and a living

bird (a tinamou), along with that of Posto-

suchus kirkpatricki, an extinct archosaur,

as an outgroup. The three extinct species

share several distinctive derived features:

for example, they have the same number

of digits and phalanges, the second digit

is longest, and the third (leftmost) digit is

twisted toward the second digit. The hand

of the modern bird is highly modified for

flight but retains these features. (Postosu-

chus hand from [5]; other hands from [35].)

16_EVOL4E_CH16.indd 415 3/22/17 1:33 PM