that looks like a banshee caliper, but is lacking the hole/mount for an e-brake ?
and the brake line connects on the bottom, instead of the top as most all yamaha rear brake calipers do ?
your best bet is to scour ebay for a matching caliper to identify it.
or replace it all, a yamaha sport quad caliper that includes the mounting bracket should bolt to that carrier
I used one like this................
http://www.ebay.com/itm/Rear-Brake-...ash=item33b9f18096:g:H1MAAOSwmtJXaxm6&vxp=mtr