OH! I have slipped the surly bonds of earth, and danced the skies on laughter's silvered wings
Sunward I've climbed and joined the tumbling mirth of sun-split clouds
And done a hundred things you have not dreamed of- wheeled and soared and swung high on the sunset silence ...
Who among us has not dreamt of flight? To coast effortlessly along on lazy thermals on a sunny day, the distant tapestry far below painted in pastel blues, browns, and greens? To dive at the ground at over 150 MPH and then pull out and blaze over a blurred landscape at breathtaking speed? From Daedalus to Da Vinci to Apollo and beyond, it is a vision that has driven mankind. The idea of flying informs our dreams, infiltrates our legends, and invades our nightmares. And now that we can fly by way of machines, it turns out to be every bit exciting as we imagined. But why are the birds heir to this ability? Why and how were they chosen to be among the lucky few who would take to the air and go on to dominate the land, sea, and sky?
Huge Grahics Below!
The most famous fossil ever found was unearthed with no ceremony in an old Bavarian stone quarry, a site known for high quality flat limestone rock called Plattenkalk since the days of Rome. It was at first a curiosity, later a sensation, and now reigns supreme among them all. It is so detailed it quickly earned the name
Lithographica; lithos as in Latin for stone, and graphos as in Greek for writing. The new find was a volume literally written in stone.
The specimen would have been a star on its own. But because of the year it was discovered, 1861 when Darwin's Dangerous idea is in full bloom having taken the scientific community by storm only two years earlier, it was propelled to fossil superstardom. The slab would become the most famous specimen preserved in the ancient medium of rock ever unearthed. But it harbored a secret kept hidden for a hundred years or more after it was dug out of the ground: The dinosaurs may not have gone extinct at all.
It looked like a lizard, down to the teeth and the tail, yet had some of the bones of a bird. And just case there was any doubt, fully functional flight feathers extending off of what look like short wings are preserved in the limestone matrix. It was called Archaeopteryx , meaning primitive wing. And it remains the oldest bird ever found.
Archaeopteryx lithographica from the Late Jurassic Solnhofen limestones of Germany. The photo above is of the real deal; the original fossil itself. Most photographs you'll see are of poor-quality casts. It ain't easy for scientists to even get near this slab. It's more valuable than diamonds
A word of caution: I have several friends who eat, breathe, and live dinosaur/bird evo AKA paleo-ornithology. They speaketh a strange language I do not understand full of morphological, anatomical, cladistics terms. But, every one of those folks is solidly behind the dinos-to-birds scenario and judges the opposing hypothesis as so bad it's in their own words "Creationist Bad". I'm not an expert. This piece may have some errors in it and I appreciate any pointers. But for the purposes of this article I've given those aforementioned dino aficionados the benefit of the doubt.
The parallels between birds and dinosaurs were not lost on early paleobiologigists. Even so eminent an evolutionary pioneer as Thomas Huxley made the case that birds might be direct descendants of dinos. But over the next few decades the Great Dinosaur Bone Wars heated up among rival fossil hunters and the emphasis shifted to bigger and meaner looking ancient beasts. Long-necked sauropods and toothy Carnosaurs soon filled the scientific literature and museum halls, and the impression of dinosaurs as big, brainless, slow moving, very unbird-like reptiles, took hold for generations.
That would not change until 1960 when Dr. J.H. Ostrom's published an exhaustive study of Deinonychus antirrhopus illuminating similarities to Archaeopteryx. That work provided the impetus for a paradigm shift in ideas on the origin of birds and the evolution of flight.
By the time Jurassic Park rolled into cinematic history, the birds were accepted as likely descendants of a dinosaur group called Maniraptors, or 'seizing hands', which includes the dromaeosaurids such as velicoraptors. The resemblance is clear:
Enlarge
I'm not qualified to delve more deeply into the anatomical congruencies between birds and dinosaurs and it's a detailed subject beyond the scope of this modest effort. For those of you so inclined, this article by Chris Nedin in the Talk Origins archive called All About Archaeopteryx is a must read.
Exactly why feathers first evolved will likely never be known. They're useful for insulation and protection, they provide a platform for coloration, and they can be used as both displays to ward off predators or attract mates. But the process of how it transpired may be coming to light, again courtesy of those wonderful fossils form China, and the relatively new field of evolutionary development.
The chart above outlines a plausible evolutionary scenario. From simple stringy feathers, to more complex stringy feathers, to flight feathers. This idea is based on the two bodies of data we do have: The variety of feathers found dinos in the fossil record and how they develop in a bird embryo.
However feathers developed, it's still a fascinating question as to how the precursors of birds learned to fly. The two possibilities are the ground up theory and the trees down theory. In the trees down theory early birds first become gliders and then refine that ability until they're capable of powered flight. In the ground up theory the small dinosaurs flapped their feathered arms while running to provide extra power and maneuvering ability. No one knows for sure which one of these broad possibilities was the path by which birds first took to the air. But once they did, feathers offered them an advantage unavailable to their aerial competitors of the day such as pterosaurs and other flying reptiles: Feathered wings are better suited to flying in and around thorny trees and bushes. If a wing of stretched skin tears on close encounter with a plant, that animals is grounded until it heals or the critter dies. Feathers aren't subject to this design flaw.
For years creationists worked very hard to discredit Archy. Most were fond of saying "It has true perching feet" as if this somehow was a problem for the same process of evolution which turned forelimbs into wings. Another objection to Archy and transitionals in general was somehting like "Every animals appears 'fully formed' in the fossil record". I'm unsure what a half-formed bird would be excatly ... a flying squirrel or a sugar glider perhaps? A deformed bird with 'half-formed' body parts would not last long. Natural selection would make quick, grisly work of such an unfortunate animal. Finding lots of adult birds that were deformed in the fossil record would be evidence against evolution.
When it began to soak into the laypublic that raptorial dinosaurs were thought to be the direct ancestor of modern birds, and when this idea excited young movie goers, the creationists of course went full tilt, adopting the existing scientific dissent over the Bird-Dino origin theory.
Most creationist nonsense on bird transitionals now comes from Answers in Genesis; the crew of the Discovery Institute doesn't talk much about birds preferring to focus on PR issue centered on philosophy or areas of mystery such as the Cambrian Explosion. But to get a taste of AiG's duplicity and see an example of how evo-devo can utterly smite them, I heartily encourage any well informed laymen to read PZ Myers' Digit Numbering and Limb development. It's short, well illustrated, written for the educated layman and that article by PZ is the best intro into evo-devo and dinosaur homology I have ever read in my life.
The competing idea to the dino origin of assigns birds as descendants of Thecodantia; an ancient clade of reptiles which predate dinosaurs and gave rise to what are called basal archosaurs which gave rise to crocodiles and turtles. The Thecodont Theory/Hypothesis basically says that birds aren't derivative dinosaurs. The primary proponents are Alan Feduccia and Larry Martin.
Then in 1995 dino hunters got lucky in an obscure quarry in the Liaoning Province of China: In series of amazing finds, one after the other, a whole new window was opened up on dinosaur evolution.
The first was this fossil of a Sinosauropteryx showing what appeared to be an exterior of stringy feathers. In rapid succession, more feathered dinosaurs were found, each one more exquisite and stunning:
Sinosauropteryx fossil in situ and artistic impression
Generic raptor fossil in situ and artistic impression
Caudipteryx fossil in situ and artistic impression
Microraptor Gui in situ and Artist's Impression
Some of the Chinese dinos are enigmatic, such as the four winged microraptor above; or any member of the Therizanosaurids. Theriz's are wierd! Most of them have these giant claws the utility of which is wide open to speculation. Scooping fish out of streams or insects out of termite mounds? We have no idea: Therizanosaurs are an excellent field of study for any of you budding paleontologists because so little is understood about these creatures. Currently Therizanosaurs are thought to be descendants of early raptors and were in the process of evolving into generalists and herbivores. If so, they plausibly had feathers, as shown below in an artists rendition.
Based on this new material, we can construct what an evolutionary progression from dinos to birds might have looked like. Again, this is not intended to represent a straight line order of ascendancy, but it does gives us a rough idea of how the transition may have occurred:
Given the new finds of feathered dinos in China, one might think the Thecodont idea would be history. But there remains one intriguing possibility: The feathered dinos of China lived more recent than archaeopteryx. That means either feathers first evolved in dinosaurs which later diversified into avian and non avian critters. Or birds did evolve from non-saurian ancestors and then later various clades of flightless birds evolved into what we think of as raptorial dinosaurs!
This Neoflightless Hypothesis is best summarized and criticized as the idea that raptors were a 'Mesozoic Kiwi' or ostrich. This idea is a long shot, I wouldn't bet even odds on it. But it is possible, it is consistent with the fossil record. We know that very large predatory flightless birds have evolved from their winged ancestors on several independent occasions. (It's also interesting that creationist use the neoflightless hypothesis to discredit evolution by way of birds and dinosaurs. Apparently a sparrow evolving into a one ton raptor is not 'macro-evolution' but going the other way is ...)
The most recent such radiation includes the now extinct Moa of Australia along with the so-called terror birds which ruled the grasslands and forests of North and South America between 65 million years ago and just a couple of million years ago. These killer birds were three meters tall in some cases, with a skull the size of a watermelon sporting a broad beak shaped like an ax blade, and at least one of them even developed rudimentary hands! So yes, it is within the realm of possibility that birds evolved into raptorial dinosaurs.
But regardless if dinos evolved into birds or birds evolved into dinosaurs, it would be correct to say that birds are a type of dinosaur. So let's take a look at a few of the dinosaurs among us.
Snowy owl Red Jungle Fowl, ancestor of the domestic chicken
A European Imperial Eagle guards its nest and chicks
A young Peregrine Falcon finishing off a tasty morsel. These are the fastest known animals and can reach speeds of almost 200 MPH when diving
Meet the Penguins courtesy of NATURE
An American Bald Eagle takes flight A Kingfisher peering into a stream prepares to strike
Birds are among the most successful of all the 'tetrapod' vertebrates with roughly 10,000 species known or suspected. Not surprising: They can pull up stakes and fly away to remote islands and oasis no other large animal can reach, or travel across the entire globe in search of warmer climes; they're equipped with the eyes of a surveillance satellite, the best in the entire animal kingdom; they have big brains and excellent memories; and if we humans don't make it, given time I wouldn't be surprised if a descendent of birds rose to sentience. Intelligent Dinosaurs: what an interesting race of beings that would be!
Perhaps one day in the not too distant future on a planet or moon of lower gravity, we too will be able to fly with the birds under our own power; to ply the alien winds as masters of the sky. Until then we can only dream of such a day and get a taste of what it might be like to soar and wheel and dance the skies on laugher's silvered wings in our clunky aircraft; and that's not a bad appetizer.
High in the sunlit silence. Hov'ring there, I''ve chased the shouting wind along, and flung my eager craft through footless halls of air.
Up, up the long delirious, burning blue I''ve topped the windswept heights with easy grace, where never lark, or even eagle flew.
And, while with silent, lifting mind I've trod The high untrespassed sanctity of space, Put out my hand, and touched the face of God