Bird Evolution Question?

Question

Yesterday, as I peered out my window in an awful mood, I was personally moved by something I've never fully appreciated in my 27 1/2 years on earth, which was the fact that birds can fly. I've always taken it for granted. It cheered me up and I'm blessed to have this big window to look out of. It got my mind on a lot of other things, and one of them is how they evolved flight. Does anyone know theories as to how it happened? What was the antecedent feature of wings? I'm assuming arms because a bird's feet look like reptile feet very much. They're curved almost like an arm too. If you have any thoughts, share them. I now know why my grandmother was a bird watcher. They are beautiful creatures.

Answer 1

The links that the female troll posted above are excellent. They'll give you probably more than you'll ever want about bird evolution.

The wings of birds are definitely homologous to our own arms, and the forelimbs of other tetrapods. They have the same bones (humerus, ulna, radius, carpals, metacarpals and phalanges) as we do in our arms, but elongated or fused by modification into wings.

The feathers are highly modified scales. They are composed mostly of keratin (the same stuff that makes up our fingernails, and the scales of lizards), and started out as enlarged scales on the ancestral reptiles - possibly for thermoregulation, or as part of a parachute/braking system for a gliding reptile.

There are two main theories as to what the driving force behind the evolution of birds from small theropod/thecodont antecedents.

The 'top down' theory is that little arboreal, climbing theropods or thecodont reptiles leaping from trees developed wings that allowed them to glide. Similar to flying squirrels and other gliding critters of today (including some varieties of snakes, frogs, lizards, and several mammals - sugargliders, feathergliders, flying lemurs, etc.), these reptiles developed wings as parachutes to slow their descent, then later for increased maneuverability and eventually to fully powered flight.

This theory fits the skeletal evidence in that the earliest birds did not have an enlarged sternum for attaching the powerful flight muscles that would help them take off from the ground, nor had they developed the strong, strut-like coracoids that keep the chest cavity from being compressed when the bird flaps its wings. However, it doesn't fit the skeletal evidence in that there are no known small theropod dinosaurs that show any evidence of adaptations that would indicate they were arboreal (there are, however, thecodont reptiles that appear arboreal - but that would mean that birds are not descendants of dinosaurs, and so it's not a 'sexy' theory).

The 'bottom up' theory is that small, fast cursorial theropod dinosaurs were chasing fast insects and other prey on the ground, and wings developed both to help their balance while running, and later also as a last second acceleration burst, with a strong wingbeat helping the dinosaur surge forward, and/or leap higher to catch their prey. They may have also used the wings to scoop prey towards them.

This fits the skeletal evidence because there are several small, fast theropod dinosaurs that fit this ecological niche, many of them show evidence of having feathers, and the skeletons of early birds like Archeopteryx are very similar to these theropods, with longer wings/arms and feathers.

It doesn't match the skeletal evidence in the lack of an enlarged sternum or coracoids that would help the cursorial create a theoretical powerful wingbeat thrust, or keep their chest from being crushed by such a wingbeat. However, bats, which are thought to have achieved flight through a similar adaptation do not have the enlarged keel of flying birds, nor the supportive coracoids, and yet they are quite capable of flight.

So the debate continues.

Answer 2

Lots of theories! One of the first bird like creatures was Archeopteryx. It had feathers and wings. and a long snout, almost like a beak. Current birds share a great deal of features with dinosaurs and many people believe that birds evolved from dinosaurs.
And for the guy below me (Tibiman) who says "evolution is a lie, god made animals the way they are". How many types of dogs were on the Ark? A pair? 10 pair? 100 pair? There are now over 6,000 species of dogs on the planet. Evolution is a fact. whether humans evolved from apes, well we can debate that. The current day sheep didn't exist in its current form (short legs, fat body) until just this past century. Bananas in most other countries are only 3 or 4 inches long.
You probably don't believe men landed on the moon. Or that the Earth orbits the sun. Is there even a sun or is it just a glowing disc that are held up by angels? Or does Apollo race across the sky in a firey chariot?

Answer 3

Scientists disagree about many aspects of the evolution of birds. Many paleontologists (scientists who study fossils to learn about prehistoric life) believe that birds evolved from small, predatory dinosaurs called theropods. These scientists say that many skeletal features of birds, such as light, hollow bones and a furculum, were present in theropod dinosaurs prior to the evolution of birds. Others, however, think that birds evolved from an earlier type of reptile called thecodonts—a group that ultimately gave rise to dinosaurs, crocodiles, and the flying reptiles known as pterosaurs. These scientists assert that similarities between birds and theropod dinosaurs are due to a phenomenon called convergent evolution—the evolution of similar traits among groups of organisms that are not necessarily related.

Answer 4

Flight probably evolved from gliding.
Feathers may have started as modified scales for insulation purposes. Some tree-dwellers survived better and reproduced more when they were able to escape their enemies and find food more efficinetly by jumping from tree to tree. Feathers prolonged the glide. Those that were able to control the glide by moving limbs or tail were more successful, eventually leading to flight.

Other reptiles evolved bat-like flight on skin wings.

Answer 5

http://www.pbs.org/lifeofbirds/evolution/index.html

http://www.evolutionpages.com/microraptor%20gui.htm

http://animals.about.com/od/birdsastudyguide/a/flightevolution.htm

http://www.ucmp.berkeley.edu/vertebrates/flight/aves.html

http://www.nurseminerva.co.uk/adapt/evolutio.htm

you asked, so here it is: several links to pages all about the origins/evolution of wings and powered flight in birds.

happy reading


PS. URFI (below) is right about the evolution thing. In short, it is called genetic mutation. it is how all living things evolve to adapt to changes.

Answer 6

evolution is a lie!
God made all animals the way they are.