I understand that the suffix, "-i," is a singular possessive
designation, and that "-orum" designates a plural possessive.
What does "-ianus" as in _Microraptor zhaoianus_ mean?
It's an attempt of making an adjective of Mr. Zhao. The idea is to make the
name mean "the Zhao *Microraptor*", like "the Church-Gilbert hybridisation
buffer" or "the Carter doctrine"; and in Latin you can't simply put two
nouns next to each other to get this effect like you can in English. Same
for *Eshanosaurus deguchiianus*.
Actually, you have this suffix in English a lot. Think of all the adjectives
that end in -ian. That's it.