Q: Connecting existing 24 inch Cinema Display to the new Mac Pro Desktop

http://support.apple.com/kb/HT5219

Using Mini DisplayPort displays or displays connecting with Mini DisplayPort adapters on Macs with Thunderbolt Ports:

18. Can I connect a Mini DisplayPort Monitor or Monitor using a mini DisplayPort adapter to a Thunderbolt port on my Thunderbolt-equipped Mac?
19. How do I connect my Mini DisplayPort Monitor or Monitor using a Mini DisplayPort adapter to my Thunderbolt-equipped Mac when I have other Thunderbolt devices connected?
20. Can I connect my Mini DisplayPort monitor or monitor using a Mini DisplayPort adapter to my Apple Thunderbolt Display?

18. Can I connect a Mini DisplayPort monitor or monitor using a Mini DisplayPort adapter to a Thunderbolt port on my Thunderbolt-equipped Mac?

Yes. A Mini DisplayPort display or a display connecting with a Mini DisplayPort to VGA, DVI, or HDMI adapter will work just like it was connecting to a Mini DisplayPort connector when plugging in directly to the Thunderbolt connector on your Apple computer. Click here for more information on Mini DisplayPort connections and adapters.

19. How do I connect my Mini DisplayPort monitor or monitor using a Mini DisplayPort adapter to my Thunderbolt-equipped Mac when I have other Thunderbolt devices connected?

When connecting a Mini DisplayPort display or a display using a Mini DisplayPort adapter to a Thunderbolt peripheral (except as described in question 14), make sure the display is connected at the end of the Thunderbolt chain. You can use only one Mini DisplayPort device in the Thunderbolt chain.

See this for adapters

http://support.apple.com/kb/HT3382

Monoprice Mini DisplayPort / Thunderbolt to HDMI®, DVI & DisplayPort Adapter

* Supports DisplayPort 1.1a "Dual-Mode" output with a maximum resolution of 2560x1600

http://www.amazon.com/Monoprice-DisplayPort-Thunderbolt-HDMI%C2%AE-Adapter/dp/B0 06F8CPPE/

http://www.amazon.com/BlueRigger-DisplayPort-Thunderbolt-Adapter-Cable/dp/B007KB 3VIU/

http://www.amazon.com/Tera-Grand-DisplayPort-Thunderbolt-Microsoft/dp/B006FKRSUY /

http://support.apple.com/kb/HT5299