Were you and your brother the only owners starting in 1981? If so, then you did not inherit the property. It was a gift from your father in 1981, and you and your brother owned it since then. Your father's death did not change the ownership of the property. If this is the case, your basis is your father's basis at the time of the gift, which is probably what he paid for the land when he originally bought it.
If all three of you were joint tenants from 1981 to 2009 - you, your brother, and your father - then you inherited only your father's 1/3 of the property when he died in 2009. Your basis for the 1/3 that you inherited is 1/3 of the fair market value on the date of your father's death. Your basis for the 2/3 that you owned since 1981 is 2/3 of your father's basis at the time that he gifted the 2/3 ownership to you, as I described above.
Either way, of course, you have to split the basis between you and your brother.
