The phrase becoming more common at thanksgiving day dinner is "It's time to carve the dinosaur", because we can no longer deny the evidence. With new DNA technology we are able to compare the "double helix" (DNA) and it's gene sequences of any organism. This field is called "molecular biology" and it's hot! It is now possible to accurately determine life's evolutionary path, and we call this "Phylogeny" or "Phylogenetics". The most common method of displaying evolutionary paths is by making "phylogenetic trees", much like a family tree.
Cladistics actually happens to be the preferred type of tree making. With this style, all pieces of the puzzle must have came from a larger piece of the puzzle. For instance, a wolf and a dog can be in the same clad, and a wolf and a coyote can be in the same clad, but a wolf, coyote, and a dog cannot be in a clad together. Alternatively, a coyote and a dog most likely will never be in the same clad.
Why is this?
Because dogs are man-made, and we know their evolutionary history, because humans created them! Dog's are a direct descendant from wolves. That's right! Every breed of dog out there evolved from a wolf, and at a much faster rate than would have happens in nature, because humans envoked artificial evolution upon these canines. Coyotes branched off from wolves on a different path then dog did. Although, all of these species can successfully interbreed a clad shows where these species become different. With strict isolation and a change in environment it would only be a matter of time before these animals change so much that they would not be able to interbreed.
Okay! Back to dinosaurs!
Due to natural occurrences in our universe ecosystems may be disrupted, causing isolation and new living conditions among species. This is particularly noticeable throughout the earths history whenever there is an "ice age" or a volcanic eruption. It was survival of the fittest (coined by Charles Darwin, an evolutionary hero) and pure luck that caused not only birds, but all extant species to be alive today.
Dinosaurs died. They probably couldn't handle the cold, or had no food. After all, our depiction of a dinosaur is a cold-blooded, hair-less, reptilian looking creature evidenced by fossil remains. One of our modern day birds ancestors was at a clear advantage due to variation that happens by a process termed "Genetic Recombination". Just like you're a combination of your 2 parents, you also have your differences. These differences grow over time so greatly that new species are formed with their own new features that may be beneficial after a sudden change in the environment. And as you can see, evolution occurs little by little, change after change, until only the most well-adapted organisms can survive, and fill a niche in an ecosystem. Fossils of an archeoteryx, have shown to be one of the birds oldest ancestors. This animal was clearly a dinosaur based on it's bone structure, but also had wings! Birds still to this day have a skeletal structure similar to many dinosaurs.
Here is the key to life. The chronological order in which life was created. At least some-what like this. It really does get a bit more complicated. Ready?
A) AMINO ACIDS->RNA->DNA->BACTERIA->PROTISTS->PLANTS
B) AMINO ACIDS->RNA->DNA->BACTERIA->PROTISTS->ANIMALS
C) AMINO ACIDS->RNA->DNA->BACTERIA->PROTISTS->FUNGI
If you don't believe me - take a simple chemistry lesson, and some basic biology lessons to learn about how molecules and DNA (deoxyribonucleic acid) really work. I was so amazed and excited to learn about biology! DNA is amazing.