Re: [dinosaur] Diplodocus status

[Tim Williams <tijawi@gmail.com>]

Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> There isn't even agreement that Diplodocus longus IS undiagnostic.

True, but beside the point.  The assessment that a particular taxon is
a nomen dubium is always subjective.

> - Even IF Diplodocus longus was undiagnostic, undiagnostic species CAN be the 
> type species of diagnostic genera.  There's nothing in the ICZN arguing 
> against that.

Just because it's not proscribed by the ICZN, doesn't necessarily mean
it's a good idea.  In fact, from a phylogenetic taxonomy standpoint,
it's a really BAD idea for a taxonomically valid genus to have a nomen
dubium as a type species.  A nomen dubium is a valid name
(nomenclature), but not a valid species (taxonomy).  Scientifically,
there's no point pretending that a nomen dubium is a valid species
simply for the purpose of nomenclature.

> - The argument about future-proofing for nomenclatural stability has zero 
> urgency because all parties involved agree Diplodocus longus is definitely 
> the same genus as D. carnegii, even the authors who
> petitioned the ICZN in the first place.  Tim et al. would be arguing for an 
> official nomenclatural change based on a case that nobody thinks is true or 
> even likely.

See response immediately above.

> - If we continue with this philosophy of designating the most complete 
> species as the type species or the most complete specimen the neotype [*snip* 
> Mickey's voluminous list of taxa] It's a bad
> philosophy.

I didn't say (or even imply) that we needed the most complete specimen
as the type species, or the most complete specimen as the neotype.
But when we have a scientifically well-known genus with a dodgy
holotype (as in the case of _Diplodocus longus_), it would be helpful
to have a species based on an unambiguously diagnostic specimen as the
new type species.

I thought Tschopp and Mateus (2016) presented a strong case in their
petition, especially this statement: "Because _D. longus_ is the type
species of the genus Diplodocus, but is itself not diagnosable, a
retention of _D. longus_ as type species would create insecurities and
confusion concerning the use of _Diplodocus_ as a genus."  Thus, the
petition aimed to resolve the "insecurities and confusion" of
_Diplodocus_.   Rebutting the petition by scouring the _D. longus_
holotype for perceived diagnostic characters does nothing to prevent
_Diplodocus_ from one day becoming a dubious genus.