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Re: [dinosaur] Latenivenatrix, new troodontid from Dinosaur Park Formation, Alberta (validity of Troodon)

According to ICZN Article 13.1.1., for a new taxon to be valid, "it
must be accompanied by a description or definition that states in
words characters that are purported to differentiate the taxon".
(This is why Lewisuchidae can be quashed in favor of Silesauridae;
even though Lewisuchidae [as Lewisuchinae] was named 22 years before
Silesauridae, it never received a formal description or diagnosis.)

Even after reading the description of _Pisanosaurus_ (a translated
version, http://paleoglot.org/files/Casamiquela_67.pdf ) I'm not
certain Pisanosauridae conforms to Article 13.1.1.
I am certain: it does not. "Diagnosis: as for genus and species" would have sufficed, but no such thing is in there.
received a description, and Pisanosauridae is erected as part of this
description... so the unique anatomical characters that distinguished
_Pisanosaurus_ from the remaining ornithischians also distinguished
Pisanosauridae at the same time.. so I guess it's okay.
That might be okay if accompanied by a mention that Pisanosaurus is the only known member of Pisanosauridae. No such thing is in the paper either! Thanks a lot for the link.
I happen to have the redescription of Pisanosaurus:
J. F. Bonaparte (1976): Pisanosaurus mertii Casamiquela and the origin of the Ornithischia. Journal of Paleontology 50(5): 808–820. Available, to some, at JSTOR.
It mentions Pisanosauridae and treats it as available, though considers it a junior synonym of Heterodontosauridae Kuhn, 1966, which explains why there's again neither a diagnosis nor a clear statement that Pisanosaurus is the only known member.
(The authors also invoke ICZN
Article, but I don't think that applies, given that
Silesauridae was named less than 10 years ago).

David Marjanovic <david.marjanovic@gmx.at> wrote:

> > Tyrannosauridae should certainly have preference over Deinodontidae.
> Of course. If you'll write a petition to the Commission, I'll join it.

We shouldn't need to. ICZN Article should mean
Tyrannosauridae can still be used in preference to Deinodontidae.
Perhaps it should, but it doesn't. Emphasis added:

23.9. Reversal of precedence. In accordance with the purpose of the Principle of Priority [Art. 23.2], its application is moderated as follows:

23.9.1. prevailing usage must be maintained when the following conditions are both met: the senior synonym or homonym has not been used as a valid name after 1899, and [...] is fulfilled, but is not, so 23.9.1 as a whole isn't either, and the prevailing usage of Tyrannosauridae counts for nothing until the Committee says it does. Have you interpreted 23.9.1 as saying that following precedence is optional if 23.9.1 is not fulfilled? It's never optional. By default precedence must be followed, in a few exceptions it must not. Emphasis in the original:
23.1. Statement of the Principle of Priority. The valid name of a taxon is the oldest available name applied to it, unless that name has been invalidated or another name is given precedence by any provision of the Code or by any ruling of the Commission.
Clearly this means that there is only one valid name of any taxon.
Pisanosauridae has (only ever) been used as a valid name after 1899; it is invalid because it never got a diagnosis, not because Silesauridae has been used more often.
I don't know if Deinodontidae has a diagnosis, but it doesn't need one: Article 13 only holds for names published after 1930. For names published before 1931, Art. 12.2.4 says the mere fact that Deinodon is an available genus name is enough.