All of those are the cores of the Athlon.
Thunderbird is the oldest. It was on the original Athlons.
Throroughbred is the latest core for the Athlon XP I believe.
Palomino was the first core for the XP.
And I have no idea where Morgan fits in. Sorry.
EDIT: The Morgan core is the new core for Duron. The original core for the Duron was the Spitfire....