Many additions and changes had to be introduced to the fertilized sauriscian eggs chosen for the first male and female birds. The angels had to essentially make a completely new zygote egg with a bunch of new DNA programming for the first bird. They had experimented with flying reptiles the pterodactyls, but these were really just gliders and quite clumsy. Of course, they made use of as much the reptilian DNA codes as they could. And after several short-lived intermediates they produced birds that were acceptable.
There were several areas of avian form and function that required new programs to be changed or added to the sauriscian eggs.
1. Skeletal changes: hollow bones for weight reduction; a large breast bone for anchoring the flight muscles; a furculum for absorbing the shock of wing motion and to act as a spring to help birds breathe while they fly.
2. Feathers for weight reduction, aerodynamics, lift and propulsion, and insulation.
3. Cardiovascular/respiratory systems: large, rapidly beating heart; lungs designed for rapid respiration rates, with openings at the top for air intake and the bottom for exhaust. All of which combines to bring large quantities of oxygen into the body and remove CO2.
4. High body temperature to allow the high metabolic rate needed to power flight.
5. Sophisticated brains were needed for keen balance and coordination associated with flight. The new brain also provided acute sensory perception and instinctive behavior. Parts of the birdbrain that were especially developed were the optic lobes, where nerve impulses from the eyes are processed, and the cerebellum, which coordinates muscle actions. The cerebral cortex, the part of the brain responsible for thought in humans, is primitive in birds. However, birds have a hyperstriatum—a forebrain component that mammal’s lack. This part of the brain helps songbirds to learn their songs, and scientists believe that it may also be the source of bird intelligence.