TES:O uses these three creatures as mascots for the different factions. Why?

The eagle has been used in elvish weapons and armor before... certainly in skyrim and oblivion. I dont recall if it made an appearance in morrowind. Is it symbolic of ascension in some way?

The lion symbol seems to be new to the series.

The dragon has always been associated with the imperials, but I could see how it would work just as well (if not more so) for the nords. I dont get how it fits the tribunal or hist... just a by-product of smashing three races under one banner maybe.

Thoughts?