Many kinds of birds have come and gone since the iconic archaeopteryx, 150 million years ago.
From a passage in Birds of the World (1961 Golden Press), Pierce Brodkorb estimated that based on the fossil record at that time that there have been between one and one and a half million species of birds since archaeopteryx. That seemed like a lot, so I checked on more recent estimates using statistics based on studies of the fossil record plus a lot of assumptions the scientists made. The estimates vary from 150 thousand to 1.5 million birds that have ever lived. Whatever the number of birds that have ever existed, there were a lot more birds that used to exist than the ten thousand-ish that exist today. Richard Pimm (who made one of the lowest estimate of total bird species) says that without humans, one species is thought, on average, to have gone extinct every 1000 years. Recently, with humans of course, it is a lot more.
Besides being sad over how much faster extinctions are happening at our hand, I come away from this with an amazement for how many different kinds of birds there were. I imagine, how many different patterns, shapes, and colors of feathers there have been which we will never know but can only try to imagine.