Re: [dinosaur] Diplodocus status

[Jaime Headden <jaimeheadden@gmail.com>]

It's not whether "Diplodocu longus" is dubious, but rather than the
holotypic material is *diagnostic*, that was the necessary question,
and this requires only the experts in the osteology to weigh in. This
was the nature of Tschopp's argument: it was not sufficiently
distinct. Much of this is weighed by the need for describers to select
unique autapomorphies not shared by almost any other taxa, or
sufficiently closely related taxa, to be "diagnostic," whereas less
weight is given to "diagnostic suites" wherein a combination of
characters are otherwise not present in other taxa, no matter how
distantly related. Supposedly, *Diplodocus longus* is substantiated by
the latter, rather than the former, and this is OK.

On Thu, Oct 15, 2020 at 1:32 PM John D'Angelo <dangelojohne@gmail.com> wrote:
>
> In my opinion, D. longus is not dubious, contrary to what Tschopp et al. 
> (2015) reported. It is clearly distinguishable from all named diplodocid 
> species except D. carnegii. If it can be distinguished from D. carnegii, it 
> is distinct from all known diplodocid species and thus valid, and if it 
> can't, it's the senior synonym of D. carnegii and still valid. I think it can 
> be, as D. carnegii has more dorsoventrally compressed caudal centra, but the 
> topic probably merits further study. However, even if D. longus was dubious, 
> the genus Diplodocus still would not be because D. longus clearly forms a 
> clade with D. carnegii and D. hallorum.
>
> Mike, I'm not sure I agree with your idea of the "effective type species." If 
> D. longus had been largely ignored since the naming of D. carnegii I might 
> agree, but while it is the less famous species it certainly hasn't been 
> ignored, although the historical conception of it was largely based on the 
> incorrectly-referred AMNH 223. It might've made more sense to petition the 
> ICZN to designate AMNH 223 the neotype of D. longus, but that would've left 
> the possibly-distinct D. longus holotype YPM 1920 nameless and so isn't a 
> particularly satisfactory solution. If it turns out that D. longus and D. 
> carnegii are not closely related, which strikes me as unlikely to happen, we 
> can cross that bridge when we get to it.
>
> On Thu, Oct 15, 2020 at 2:28 PM Mike Taylor <sauropoda@gmail.com> wrote:
>>
>> Yes, it's based on Diplodocus longus: the ICZN rejected a petition to change 
>> the type species to D. carnegii a couple of years ago. I submitted a comment 
>> in support; IIRC Mickey Mortimer submitted one against :-)
>>
>> What does this mean? The petition was rejected partly on the grounds that 
>> the D. longus material was (wrongly in my opinion) considered sufficiently 
>> diagnostic, so the genus is OK. (I mean, by definition it's OK 
>> nomenclaturally, but it should be OK taxonomically.) But in practical terms, 
>> everyone who works on sauropods still means "kinda like D. carnegii" when 
>> they say "Diplodocus". No-one cares about the type material. So all that's 
>> happened is that the rejection of petition means that the nominal type 
>> species is not the same as the effective type species. If it ever turns out 
>> the D. carnegii is generically separated from D. longus, you can bet for 
>> sure that it will be carnegii that retains the name Diplodocus, whatever the 
>> ICZN may say.
>>
>> -- Mike.
>>
>>
>>
>>
>> On Thu, 15 Oct 2020 at 20:14, Ethan Schoales <ethan.schoales@gmail.com> 
>> wrote:
>>>
>>> What's the status of Diplodocus's type genus? Is it still D. longus, which 
>>> is apparently dubious?
>>>
>>> I hope Diplodocus doesn't end up as a dubious genus.



-- 
Jaime A. Headden
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