"The natural name for Leiothrichidae is Garrulacidae (based on the oldest named genus). However, the ICZN insists on keeping separate books for family-level names and for genera, meaning that the oddly spelled term Leiothrichidae is correct. I do not know why the ICZN does this instead of simply extending the genus name system where the oldest-named generic type determines the genus name. It would be much simpler to also use the oldest-named genus to determine the family name. Gelang et al. might have been able to abandon Leiothrichidae due to lack of use, but they have endorsed it (as Leiothrichinae) instead.
I don't think they could have done that; at least not unless Garrulacidae had already been very extensively used, which it is not.
In terms of priority, the ICZN indeed regards family-group names as completely independent from the genus-group names on which they are based. The dates you have to consider to establish priority between family-group names are the dates of the publications that made them available as family-group names
the dates of publication of their type-genera.
(Exactly as the dates you have to consider to establish priority between generic names are of course the dates of introduction of the generic names themselves, not those of the descriptions of their type-species.)
Of course, treating family names as "super genus-group names" would be possible, had we to construct a new system today out of nothing. But this is simply not how the system was designed from the beginning, and turning to such a method would make a huge number of family names suddenly incorrect (e.g., Carduelidae should become Loxiidae, etc...).
The most extensive work on bird family-group names to date is probably that of Bock 1994 - http://digitallibrary.amnh.org/dspace/handle/2246/830
. (It is not perfect, though, and the claims it makes are probably always best double-checked.) What it suggests in the present case is:
Leiotrichidae Swainson, 1832 ("1831"), is based on Leiothrix
Garrulacidae Bonaparte, 1850, is based on Garrulax
If so, Leiothrichidae has priority over Garrulacidae, because it was published first. Garrulax
indeed has priority over Leiothrix
, but this is irrelevant.
(Re. spelling: Leiothrix
derives from λειος
) = smooth + θριξ
) = hair. Family-group names are formed from the stem of the genitive case of the genus name on which they are based. The genitive of θριξ
), thus the stem to be used is thrich
*, and Leiothrichidae is indeed correct.)
Edit - Incidentally, Garrulax
is not the oldest named genus of the group. Turdoides
Cretzschmar, 1827, is older.