Perhaps this helps? From Wiki;
"One of the central motifs of Mithraism is the tauroctony, the myth of the slaying of a sacred bull. In the Graeco-Roman myth, Ahura Mazda sent a crow, which instructed Mithra to stab the animal for the sacrifice. This myth is one of the better indications that Graeco-Roman Mithras does not stem from Zoroastrian Mithra; since in later Zoroastrianism texts (Vendidad 21; Rivayat 386) and in Persian mythology it is Angra Mainyu (Ahriman in later Persian) who slays Gavyokdat, the primeval bull created by Ahura Mazda (cf: bas-relief from the Apadana Hall, Persepolis). In the Graeco-Roman myth, from the body of the dying bull spring plants, animals, and all the beneficial things of the earth. In contrast, in the Persian myth, Mah (the moon) rescues the essence of the dying primeval bull, and from it springs all animal creation."
© Charles N. Pope, US Library of Congress. All rights reserved.