Evolution, 4th Edition

450 CHAPTER 17

Tetrapod lineages (“amphibians”) diversified in the Carboniferous. Some of them

(anthracosaurs) are intermediate between amphibians and reptiles, and have been

classified as both by different researchers. Anthracosaurs gave rise to the first known

amniotes^3 , the captorhinomorphs. By the late Permian these primitive amniotes

gave rise to the synapsids, which included the ancestors of mammals and increasingly

evolved mammal-like features (see Chapter 20). The first amniotes also gave rise to

the diapsids, a major reptilian lineage whose descendants, as we will see, domi-

nated the Mesozoic landscape.

The end-Permian mass extinction

During the Permian, the continents approached one another and formed a single

world continent, Pangaea (FIGURE 17.19A). Collisions between land masses built

the Appalachian, Ural, and some other mountain ranges, sea level dropped to

its lowest point in history, and climates were greatly altered by the arrange-

ment of land and sea. The Permian ended, 252 Mya, with a catastrophe: the

(^3) Amniotes are those vertebrates—reptiles, birds, and mammals—with a major adaptation for
life on land: the amniotic egg, with its tough shell, protective membranes (chorion and amnion),
and a membranous sac for storing waste products.
Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_17.18.ai Date 02-16-2017
Crustacea (crustaceans)
O
I
W
WF
RT
S
CM
Collembola (springtails)
Zygentoma (silversh)
Odonata (dragonies)
Orthoptera (grasshoppers)
Blattodea + Isoptera (roaches + termites)
Hemiptera (bugs, aphids, lice)
Hymenoptera (wasps, bees)
Coleoptera (beetles)
Lepidoptera (moths, butteries)
Siphonaptera (eas)
Diptera (ies)
550 500 200250300350400450 0 Mya
FIGURE 17.18 A phylogeny of some of the orders of living
insects, showing estimated dates of branching events. The origin
of insects from crustaceans is marked O at the basal branch point.
The true insects, as defined by the structure of the mouthparts,
diverged from the springtails and related forms at the branch
marked I. Basal lineages of insects, such as silverfish, lack wings.
W marks the evolution of wings in the ancestor of all the other
orders, and WF the evolution of wing folding: the ability to fold
the wings over the back instead of holding them permanently
outstretched, as in dragonflies. RT marks the origin of a clade
that includes the grasshoppers, roaches, and many other forms.
The termites (Isoptera) evolved from roaches. The Hemiptera, or
true bugs and relatives, have mouthparts modified for sucking
(S) plant sap or animal body fluids. CM marks the evolution of
a profoundly important feature: complete metamorphosis. The
wasps, beetles, moths, and true flies, with distinct larval and pu-
pal stages, include huge numbers of species. (After [66].)
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