Easiest tip to survive from it specially if you are a low level is to quickly find a paracathireium(the mini bronco guys) or if you are close to any large creature,fly under or around them and the rhynio will lose it's agro from you tame. If it doesn't in your case then RIP to your lovely dino. I had an encounter with them when I was going from redwood swamp and literally 5 of 100+ jumped on my nearly maxed out argy. The swamp and big and I was in panic so I just kept flying and thought to say my final goodbye to my love my argy but suddenly when I had 200 hp left a group of diplo,paracethirum and bronto was just outside the edge of that swamp. I didn't notice them but was going from that side so I just sweeped under one of them and afterthat I was saved. None of the rhynio came to me but rather started demolishing every freaking large creatures infront of me. Since I knew I was safe, I just sat down to see the brontos and others get obliterated. My argy too only had below 2k hp from his 10-12k hp but damn never gonna forget this incident.