User blog comment:Kogath/Monster Hunter: World Discussion/@comment-26127701-20180615010002/@comment-8985329-20180615181845

Same page says: With the new additions to this classification, the common traits of the Fanged Wyverns have been narrowed to being quadrupedal and having wingless limbs. So yeah, they aren't synapsids or anything like that, just big lizards lol