Geoscience Reference
In-Depth Information
The same would have happened with islands, in which ocean currents or storms
would have given these seeds a one-way ticket to a new home. Who needs birds?
Floweringplantsdo.Thehugedifferencebetween“pre-birds”and“post-birds”
for flowering plants was in rates of long-distance dispersal, which with the assist-
ance of birds became hundreds of times faster and much more regular than relying
on mere chance. Multiply these faster rates by the cumulative effects of generations
of birds and angiosperms, and then add the effects of migrations to this equation.
For instance, if Cretaceous birds started to move great distances annually, includ-
ing over mountains and seaways that previously were barriers to plants and their
seeds, the geographic spread of angiosperms would have accelerated dramatically.
Birds aiding the long-distance dispersal of flowering-plant seeds—through eating
fruit, carrying seeds, and defecating—must have transformed landscapes in an as-
tonishing way over the last half of the Cretaceous Period. This Mesozoic crap was
evolutionary gold.
How do ingested seeds resist digestion? Most have a hard coat that enables
them to pass through the harshest of acidic digestive systems unscathed. This even
happens in the guts of alligators and crocodiles, some of which eat a surprising
amount of fruit. The bonus for these seeds is that they temporarily stay in a warm,
moist place—namely, an animal's digestive tract—exit that place with a good
amount of high-quality plant food on top, and grow up in a place different from
where their parents lived. Birds make this happen more than any other animals.
Granted, mammals do their part in playing the role of Johnny Appleseed, too, as
a huge number of mammals are fruit eaters and very good at taking seeds to new
places. Forinstance, fruitbats,justifying theircommonnames, eatfruits,flytooth-
er places, and defecate seeds covered with wondrous bat guano.
However,thebigdifferencebetweenbirdsandmostmammals(includingbats)
is in their evolutionary histories. Throughout much of the Mesozoic Era, mammals
were subordinate to dinosaurs in their shared ecosystems, and as far as we know no
mammals evolved powered flight until nearly 15 million years after the end of the
