Recently identified genetic defect, Developmental Duplication, in Angus cattle, sometimes results in 'extra' limbs, but sometimes only manifests as abnormal flaps of skin. Polymelia(extra limbs) is seen in numerous breeds, and sometimes is just an 'accident', as might be the case for your calf, with this flap of skin.
But... the DD defect in Angus cattle has been traced back to several prominent Angus sires from the 1970s-80s, Ken Caryl Mr. Angus, R&J Spade, and, I think, Fairfield Hi Guy - and in several recently popular Angus sire lines that go back, especially to KC Mr. Angus.
So many breeds have incorporated Angus genetics since the '60s, that this defect may have 'hitch-hiked' along undetected for many generations, and may be more widespread in other purebreds than some folks realize.
Dr. Denholm(Australia),who's been one of the leading investigators, has an article on recent developments, with link to his Photobucket gallery of photos, here:
http://www.flockandherd.net.au/cattle/reader/developmental%20duplication%20angus.html