Evolution, 4th Edition

THE HiSToRy oF LiFE 453

TERRESTRiAL PLANTS AND ARTHRoPoDS For most of the Mesozoic, the flora

was dominated by gymnosperms (seed plants that lack flowers). The major

groups were the cycads (FIGURE 17.22A) and the conifers and their relatives—

including Ginkgo, a Triassic genus that has left a single surviving species as a “liv-

ing fossil” (FIGURE 17.22B,C). A major event in life’s history is the rise of the angio-

sperms, the flowering plants, which evolved from a gymnosperm ancestor in the

late Jurassic and became fairly diverse by the early Cretaceous (FIGURE 17.22D)

[31]. A well-calibrated DNA phylogeny shows that the major modern groups

of angiosperms were diversifying rapidly in the early Cretaceous; for example,

monocot lineages such as orchids, palms, and grasses had diverged by about

130 Mya [58]. By the mid-Cretaceous, about 108 Mya, the world’s forests were

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(A) (B) (C)

FIGURE 17.21 Features of marine predators and prey that escalated during and after

the Mesozoic marine revolution. (A) The huge claws of modern lobsters represent a

trait found in several crustacean groups. Such claws enable some lobsters and crabs to

crush and rip mollusc shells. (B) Spines on both bivalves and gastropods (such as this

Murex) prevent some fishes from swallowing these prey and may reduce the effective-

ness of crushing predators. (C) Thick shells and narrow apertures, as in the gastropod

Cypraea mauritiana, deter predators.

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(C)

(D)

(A) (B)

FIGURE 17.22 Seed plants. (A) A living cycad (Encephalartos sp.). Gymnosperms

were abundant and highly diverse during the Mesozoic, but only about 130 spe-

cies survive today. (B) A fossilized Ginkgo leaf from the Paleocene (66–56 Mya).

(C) A leaf of the sole surviving ginkgo species, Ginkgo biloba. (D) Protomimosoi-

dea, a Paleocene/Eocene fossil member of the legume family, an angiosperm

group that includes mimosas and acacias. (D courtesy of W. L. Crepet.)

17_EVOL4E_CH17.indd 453 3/22/17 1:37 PM