Geoscience Reference
In-Depth Information
Yetbirdsdidnotjustferryaboutthepotentialoffspringofplantstoislandsand
other places: they also carried animals. Given this thought, it might be tempting to
conjure an image of an avian airlift in which squadrons of cranes and storks on a
continentallandmasseachgraspasmallmammalorlizard,andonebyoneflythem
to the nearest island and drop them off. They would then repeat this over genera-
tions, but taking these vertebrates to different islands, and farther afield. Assuming
that each payload included both males and females of those animals, the islands
eventually all got colonized. End of story.
Well, not quite. If birds want to go long distances without exhausting them-
selves, they are much better at handling very small passengers, ones they do not
even notice as stowaways. These hitchhikers also can ride in larger numbers, which
improves their chances of reproductive success when they arrive at their new des-
tinations. Animal immigrants could include members of these birds' microbiomes,
such as lice and other skin parasites, but other accidental tourists—such as snails,
larval insects, or larval crusta-ceans—also can attach to bird feet. The best feet for
these animals to latch onto are webbed ones, which have the most surface area;
moreover, webbed feet tend to step into environments with lots of aquatic larvae.
This means that ducks, geese, seagulls, pelicans, and other birds with webbed feet
(palmate and totipalmate) are among the best candidates for taking off with the
highest number of inadvertent travelers. The likelihood of this scenario is further
improved if those bird feet step into mud, which acts as a temporary glue for stick-
ing seeds and tiny invertebrates onto their pilots.
BasedonfossiltracksfromKorea,weknowthatpalmatebirdfeethadevolved
by about 120
mya
(Early Cretaceous). Moreover, webbed bird tracks became more
common and bigger throughout the rest of the Cretaceous. This meant that more
birdsevolvedtoshorelinehabitats,andhenceweremorecapableofpickinguplittle
invertebrates ontheirfeet,takingthemtoecosystemsandplacestheirancestorshad
neverbeforeexperienced.Allofthisimpliesthatperhapsthelargestlivingtracesof
