Why can teratorn-sized eagles be bred?
Many possible reasons. Most simply, because (according to Ted’s sources) breeding eagles for size has only been going on for a few thousand years. Evolutionary processes are thought to take hundreds of times that long. Further, teratorns may have depended on conditions that don’t exist today, such as long-term stable atmospheric conditions in the area that they evolved that don’t exist in the Mongolian region where Ted’s alleged eagle breeding occurs.