User blog comment:Dracosaurian/Discussion of The Week: Monster Rivalries/@comment-25033519-20141124030128/@comment-5963861-20141124032042

The rivalry between those two started when Amatsumagatsuchi drove the Zinogre out of their original home, thus causing them to go into Yumko/Misty Peaks. Zinogre have since hated the elder dragons and you can even see a Zinogre confront an Amatsu in the begining of MHP3rd.