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Barremian

Figure 18.22 The coevolution of floral structures and of pollinating insects during the entire span of the Cretaceous and the early part of the Tertiary. Some of the major floral types are (a) small simple flowers, (b) flowers with numerous parts, (c) small unisexual flowers, (d) flowers with parts arranged in whorls of five, (e) flowers with petals, sepals and stamens inserted above the ovary, (f) flowers with fused petals, (g) bilaterally symmetric flowers, (h) brush-type flowers, and (i) deep funnel-shaped flowers. Pollinating insects include (j) beetles, (k) flies, (l) moths and butterflies, and (m-q) various groups of wasps and bees: (m) Symphyta, (n) Sphecidae, (o) Vespoidea, (p) Meliponinae, and (q) Anthophoridae. (Based on information in Friis et al. 1987.)

Figure 18.24 Rapid radiation of the angiosperms during the Cretaceous, shown by the rise in the number of angiosperm families, from none at the beginning of the Cretaceous to more than 35 by the end of the period. Neocom, Neocomian; B, Barremian; Ce, Cenomanian; T, Turonian. (Based on information in various sources.)

Figure 18.23 Fossil angiosperm remains from North America. (a) Flower of an early box-like plant, Spanomera, from the mid-Cretaceous of Maryland (x10). (b) Leaf of the birch, Betula, from the Eocene of British Columbia (x1). (Courtesy of Peter Crane.)

Figure 18.23 Fossil angiosperm remains from North America. (a) Flower of an early box-like plant, Spanomera, from the mid-Cretaceous of Maryland (x10). (b) Leaf of the birch, Betula, from the Eocene of British Columbia (x1). (Courtesy of Peter Crane.)

250 of the 400 or so extant families of angio-sperms have a fossil record of some kind.

Angiosperms and climate

Angiosperms are highly sensitive indicators of paleoclimates on land, and they provide the best tool at present for estimating temperatures, rainfall patterns and measures of sea-sonality. The key to the use of angiosperms in this way is the fact that so many modern taxa may be traced well back into the Tertiary and Cretaceous, and paleobotanists assume that adaptations that are observed today had the same functions in the past.

Studies on North American Late Cretaceous angiosperm leaves have shown how precise these climatic estimates may be. Upchurch and Wolfe (1987) established ways

Figure 18.24 Rapid radiation of the angiosperms during the Cretaceous, shown by the rise in the number of angiosperm families, from none at the beginning of the Cretaceous to more than 35 by the end of the period. Neocom, Neocomian; B, Barremian; Ce, Cenomanian; T, Turonian. (Based on information in various sources.)

of assessing temperatures and rainfall measures from key leaf features, such as:

1 Leaf size: largest leaves are found in tropical rain forest, and size diminishes as temperature and moisture decline.

2 Leaf margins: in tropical areas, most angiosperm leaves have entire (unbroken) margins, whereas in temperate areas there are many more tooth-margined leaves.

3 Drip tips: leaves from tropical rain forest species have elongated tips to allow water to clear the leaf during major downpours.

4 Deciduousness: the proportion of deciduous trees (those that shed all their leaves simultaneously in winter or during the dry season, that is, times of low growth rate) to evergreens is highest in temperate zones, while tropical trees are more likely to retain their leaves since they grow more continuously.

5 Lianas: certain angiosperms in tropical forests grow as long, rope-like plants that hang down from tall trees (see any Tarzan film), but such plants are uncommon in temperate forests.

6 Vessels in wood: in areas subject to freezing or drying, the vascular canals possess adaptations to prevent air filling the canals

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