Unlike many of Cisco's other CCNA certifications, the CCNA DC certification does not require the CCENT or CCNA Routing and Switching certification as a prerequisite. However, because the DCICN 640-911 exam overlaps so much with the ICND1 100-101 exam (part of the CCNA Routing and Switching certification), if you have already studied for the CCNA R&S, you will have completed some of your CCNA Data Center study.
As for the literal prerequisites, Figure 2 shows the current CCNA certifications, with the minimum prerequisites. Currently, only the CCNA Data Center, CCNA Video, and CCNA Service Provider certifications do not require at least a CCENT certification as a prerequisite. (These requirements can change over time; always check again at http://www.cisco.com/go/certifications.)