A layman tries to come to grips with raptor evolution
In the Winter of 2008, when we first had significant numbers of educational raptors in outside enclosures, the mercury plunged one night in February to minus 29 degrees. I wasn’t worried about the migratory raptors, as they all have thermostatically controlled, heated bird houses, but I couldn’t sleep, worrying about our Great Horned Owls and other non-migratory residents, so at 2:00 AM, I put on my thick winter coat, donned a head lamp, and went outside to have a look.
Utah, my favorite great horned owl, and frequent glove companion during many presentations, had lost his wing at the wrist, in a collision with a car in Utah the year before, and had become a non-releasable education bird, sent to us by our friend Debbie, who runs a rehab facility called “Second Chance” (http://wildliferehabilitationinutah.blogspot.com). While I walked out to the large enclosure Utah shared with a female named Artemis, I noticed Cree, our wolf hybrid, tucked into a ball in the corner of his enclosure, with the end of his tail covering his nose. I remember thinking to myself, now this is cold, and I half expected to hear the air freeze in place, fall and shatter on the path before me. To my surprise, Utah was perched in his usual place, out in the weather, nowhere near the wind-curbing overhang and roosting box, where Artemis had sought shelter, and he looked at me like I was the one who might need respite from the cold. Now, I'm not a biologist, but this was a lesson I took to heart.
Like most folks, I long assumed that feathers had developed slowly over time to enable flight, but I’d never really considered how this would happen. The Creationist taunt, “what good is half a wing?”, seemed like a reasonable question. A fossilized archaeopteryx, which means “ancient wing”, and who lived in the late Jurassic period, about 150 million years ago, was discovered in Germany 150 years ago, about the time Darwin explained how Natural Selection was the driving force behind Evolution. The crow-sized archaeopteryx had a mouth full of teeth, claws for grasping and a reptilian tail, but it was also pretty clear that this was an animal that flew, and since its feathers were not dramatically different in shape from the feathers of modern birds, it was christened the first bird.
Twenty years ago, paleontologists began discovering that many theropods, the
who walked on their hind legs, were feathered.
Theropods included some herbivores and
omnivores, but are more generally associated with fearsome carnivores,
like Velociraptor and Tyrannosaurus, stars of the Jurassic
Park movies. Furthermore, some of these theropods predated
archaeopteryx, and their feathers, unlike those of archaeopteryx, were
symmetrical, meaning that they would not have assisted in providing the
that enables flight.
Their wrist bones, however, had evolved in a
fashion that allowed them to whip their long clawed fingers forward,
presumably to grab prey with, but also in a manner that would become
the flight stroke in modern birds. Many of these theropods were also
hollow boned, a feature that would make them lighter, adding speed to
both their hunting and fleeing capability. At some point, mutations
must have produced asymmetry in the feathers, which aided in gliding by
providing lift. As natural selection works, the possessors of these
feathers were better suited to escape from their unsentimental, larger
theropod cousins, analogous to how flying fish escape their
pursuers, and they could leap a bit higher in pursuit of prey, glide a
bit further, and as a result, they were more likely to survive and pass
these feathers along to their offspring.
Okay, back to Utah and that cold Adirondack
night. Vertebrates are animals with backbones,
and it turns out that feathers, which are composed of one of nature's
plastics, beta-keratin, a stiff fibrous protein also found in talons,
beaks, and reptilian scales and shells, are the best vertebrate
superior to mammalian fur, which is sort of ironic, since mammals would
supplanting the large dinosaurs wiped out when that big comet decided
the Gulf of Mexico at the end of the Cretaceous, 65 million years ago.
The hair, nails and claws of mammals contain alpha-keratin, a less
complex fibrous protein.
addition, we all know that feathers can grow in a variety of colors, so
great for display purposes. Raptor females are almost always larger
males, and approaching males are as likely to be attacked by the object
of their affection, as to have their amorous advances indulged.
Colorful feathers allowed males to woo females from a safe distance,
but also could be displayed to warn other males to back
off. Even in nature, threats of violence are safer and less
counterproductive than an actual attack, which could seriously injure
both males. In other words, feathers provide an example of a feature
evolved for one purpose, in this case, heat retention and further on,
with the lengthening of flight feathers and their evolving asymmetrical
ended up enabling flight, as well as the survival of those raptors who
could glide or fly.
Meanwhile, some large scary birds survived
with those birds
who are the ancestors of our modern birds. In fact, for a stretch from
million years ago, right up until about 2 million years ago, not long
after our ancestors
began climbing down from trees,
and homo habilis began gradually fanning out of Africa, the
7 foot tall, 400 pound “Terror Bird”, developed into the velociraptor
of it's day, becoming the dominant predator in South America, up until
the appearance of saber-toothed cats. The terror bird had a beak the
size of an NFL player’s
helmet, and huge talons which could disembowel the
unfortunate ungulates and plains dwelling creatures it caught up with.
The evolution of today's birds of prey,
scaled down to a size commensurate with the smaller creatures they prey
on, masks a remarkable evolution, and a link to a past when their
ancient ancestors ruled the earth for nearly 150 million years.
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