On ThinkMarkets a while back, I was pointing out that even as simple a "fact" as that "a camel is a mammal" is theory-dependent. Well, I was just reading Sir Richard Southwood's book, The Story of Life, and he listed the three major groups of reptiles, according to his (2003) view:
1) turtles and tortoises;
2) proto-mammals and mammals; and
3) dinosaurs, crocodilians, lizards, snakes, and birds.
It just goes to show ya. Before I'm gone from this vale of tears, I'm sure I'll discover that eagles are actually a form of slug, or something of the sort.