Geoscience Reference
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Cretaceous. On the other hand, the earliest birds that evolved from non-avian dino-
saurs likely witnessed the first flowers. Although flying insects were also around
then, they played more of a role in eating other plant parts and pollinating; in most
instances, they would have been too small to carry seeds elsewhere. In other words,
plantsandbirdshavehadamuchlongertimetogettoknowoneanotherinanevol-
utionarysense,andthisco-dependencyissodeeplyrootedthatmammalshaveonly
added to the apple cart, not yet upsetting it.
Like all co-dependencies, though, a dark side emerges when one asks: What if
I am a bird who does not carry out a plant's wishes? For plants, revenge is a dish
bestservedfruity,assomefloweringplantsdiscourageseedeatingbypoisoningan-
imals that dare to digest their seeds. For instance, apples and cherries are perfectly
fine foods for humans and many other animals. But do not chew and swallow, say,
a cup of apple seeds: every seed contains a small amount of cyanide, a very nasty
toxin that interferes with oxygen absorption. Likewise, cashew nuts, which are the
seeds inside the fruits of cashew trees (
Anacardium occidentale
), have poisonous
shells, so every nut must be extracted from its shell before enjoying them. Hence,
flowering plants useda“carrot andstick” approach intheir co-evolution with birds.
First,rewardanimalsthateatyourfruit,carryyourchildrentoanew,far-awayland,
and “plant” it with droppings there. Second, punish animals that try to take their
hunger one step further by eating your children.
The role of birds in specially delivering plant seeds to novel places is now
well documented, particularly for islands. Charles Darwin even thought of this, as
he wondered how the isolated Galapagos Islands off the coast of South America
had managed to acquire such thriving plant communities. Ocean currents and
winds—which can transport seeds long distances—certainly played a role. But this
assumes too much: after all, not every seed floats, nor do all seeds survive being
immersed in salty water for long journeys, nor does each seed stay aloft once air-
borne. They needed help, and birds stepped in to do this, probably starting in the
Cretaceous.
