I'm intrigued by the azarae vs azarai situation, so I have asked about it on the nomenclature part of Birdforum because there are members there who specialise in this sort of thing. I'll let you know what I find out.
a reply I received on the Birdforum thread I mentioned is that the specific name being azarae is due to treating the name as a first-declension masculine, which works. I'm not sure if it is completely accurate to do so given that it is a person's name, but it does mean it is not wrong (if that makes sense).So the Central American Agouti is D. punctata rather than punctatus due to the gender of the word Dasyprocta but D. azarae should really be D. azarai because in this case it's the eponymous person's gender that matters. So D. azarae as a name is not compliant with the ICZN - I'm sure at some point someone influential will notice!![]()
a reply I received on the Birdforum thread I mentioned is that the specific name being azarae is due to treating the name as a first-declension masculine, which works. I'm not sure if it is completely accurate to do so given that it is a person's name, but it does mean it is not wrong (if that makes sense).
"ae" is how Latins most generally wrote "ai"... (Unless the 'i' had a consonant function, that is--but we would now usually write the letter 'j' rather than 'i' in most such cases.)
Masculine personal names with a genitive in -ae are in no way unusual. Standard Latin names (classical nominative in -a): Numa, Catilina, Murena (genitive Numae, Catilinae, Murenae); also names inherited from Greek with nom. in -as: Aeneas, Lucas, Judas, Thomas (gen. Aeneae, Lucae, Judae, Thomae); as well as a few other such names in -es: Anchises (Aeneas' father), Perses (gen. Anchisae, Persae).
Otoh, second-declension nouns or names in -aus are basically non-existent in Latin. (The only genuinely Latin nouns with a nominative that ends in -aus are fraus, gen. fraudis, and laus, gen. laudis: both third-declension words, and both feminine...) However some Greek masculine nouns/names in -αος were used by Latins in a way that produced genitives in -ai (eg. Greek Μενελαος, in Latin Menelaus, gen. Menelai). A name or noun with an -ai ending in a Latin text looks immediately pretty exotic, though.
The Code explicitly allows both endings: -ae (under Art. 31.1.1) and -ai (under Art. 31.1.2) (see the treatment of Poda International Code of Zoological Nomenclature), and protects the original spelling.
Groves used azarai for Aotus azarae in 1993, citing "Art. 31" of the ICZN (but overlooking 31.1.1 and 31.1.3). In 2005, he himself reverted to the original spelling.
(Note that "a ruling of the ICZN" would be a decision made on a specific case by the International Commission of Zoological Nomenclature. There was no ruling here, I believe; it was just a personal interpretation of an article of the International Code of Zoological Nomenclature.)