Travel Reference
In-Depth Information
In the 1980s Bruce Tif ney, then at Yale's Peabody Museum, made an
astounding discovery. As fl owering plants took over the forests they under-
went an enormous evolutionary change. Their average seed size, which
was tiny when the dinosaurs were dominant, suddenly increased by ten- to
a hundred-fold at the beginning of the Age of Mammals. The average has
stayed at these large sizes ever since.
3
Why this rapid increase in size? Tif ney points out that in dense forests large
trees must produce large seeds and fruit if they are to ensure that their seeds will
be well dispersed by animals and birds. Large animals and birds are attracted to
such large seeds and fruit, which provide the substantial packets of energy they
need. The large animals will carry the seeds they don't eat to places far from the
parent tree, where they have a chance to grow up into the canopy.
But, Tif ney suggests, this evolution toward larger seeds and fruit only
became possible when large mammals and plentiful fruit-eating birds had
replaced the dinosaurs. The dinosaurs tended to be rather unimaginative
when it came to cuisine, and had less demanding metabolisms than mam-
mals. Herbivorous dinosaurs simply chewed up entire plants, perhaps
fermenting them like the animals we met in Chapter 2. They did not take
advantage of the concentrated sugars, fats, and proteins that were of ered by
the fruits and seeds of fl owering plants, in part because these of erings were
so skimpy. A giant brontosaurus could not survive by nibbling on teeny-
tiny fruits and seeds.
In contrast, herbivorous mammals evolved to take advantage of the good-
ies provided by the fl owering plants, right from their origin during the Meso-
zoic. The small mammals, unlike the dinosaurs, could move into the ecologi-
cal niches provided by these tiny but energy-rich nibbles. Seed-eating was a
boutique niche, allowing only small populations of small-sized mammals
Figure 75
(
opposite
) This
Banksia prionotes
from western Australia is pollinated by a wide
variety of birds, but the pollination success rate is low. The orange infl orescence matures into
an infructescence, such as the one you see at the lower right. Only a few of the fl owers of
the infl orescence were pollinated, and each of these double fertilizations has triggered the
development of large brown seed-containing follicles. The mechanism of double fertilization
enables the plant to make seeds only from its fertilized eggs, enabling it to save large amounts
of energy.
