[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Suchosaurus, Baryonyx and Martinavis
Mike Keesey wrote:
> But "dubious" is relative to taxonomic level. For example, it may not
> be clear whether the organism represented by the type specimen of
> _Troodon formosus_ belongs to the same species as the organism
> represented by the type specimen of _Stenonychosaurus inequalis_, so
> it could be considered dubious at the "species level". (I'll ignore
> for now the problems with the concept of a "species level", especially
> in paleontology.) But do they share more recent common ancestry with
> each other than with _Dromaeosaurus albertensis_ or _Vultur gryphus_?
> Quite likely, yes.
> Furthermore, someone correct me if I'm wrong, but I don't think the
> ICZN has any official stance on whether a name is "dubious" or not.
> (And I know the PhyloCode doesn't.)
Ah, deja vu all over again. :-)
I think we've been through this before, though not with _Troodon_ as the casus
bellus. Remember the Great Mochlodon War of 2006?
(http://dml.cmnh.org/2006Jun/msg00398.html, and so on...)
The take-home message is that while the ICZN does not *rule* on nomina dubia,
it does have rules concerning higher-level classification when a species does
*not* have a valid specimen as its type specimen. This is bound up with the
principle of hierarchial typification (Article 61.1.2)...
"Objectivity provided by typification is continuous through the hierarchy of
names. It extends in ascending order from the species group to the family
group. Thus the name-bearing type of a nominal species-group taxon is a
specimen or a set of specimens (a holotype, lectotype, neotype or syntypes
[Art. 72.1.2]), that of a nominal genus-group taxon is a nominal species
defined objectively by its type; that of a nominal family-group taxon is the
nominal genus on which its name is based."
So to return to the current example... if _Troodon formosus_ is not
*taxonomically* valid at the level of species, then the genus is not valid
(because of the nature of its type). And if the genus _Troodon_ is not valid,
then Troodontidae is not valid (in the nomenclatural sense) because of this
step-wise hierarchial typification. In short, a family is tied to its type
genus, and a genus is tied to its type species, and a species is tied to its
type specimen(s). But you can't skip a step: it's strictly hierarchial. So
says the ICZN.
When you ask a perfectly reasonable question like "But do they [_Troodon_ and
_Stenonychosaurus_] share more recent common ancestry with each other than with
_Dromaeosaurus albertensis_ or _Vultur gryphus_?", I agree the answer is "Yes".
But this is irrelevent to the ICZN. If _Troodon formosus_ cannot be
maintained as a valid *species* (taxonomically speaking), then it has a cascade
effect in invalidating all coordinated family-level groups, including
Troodontidae. This came up with _Titanosaurus indicus_: when Wilson and
Upchurch (2003) claimed _T. indicus_ was a nomen dubium (i.e., nomenclaturally
valid, but taxonomically invalid), it had a domino effect in knocking over
Titanosaurinae, Titanosauridae and Titanosauroidea, per ICZN rules.
Thus, taxonomy (in this case, the diagnostic nature of a type specimen) has
repercussions for family-level nomenclature. The ICZN is not explicit on this
point, in that it does not mention the terms "nomen dubium" or "nomen vanum" in
this context; but 61.1.2 makes the overarching intent clear. This hierarchial
typification mandated by ICZN is one issue on which ICZN disagrees with the
> Actually, wouldn't the ICZN-required name be "Megalosauroidea"?
> (Speaking of potential nomina dubia....)
Ah yes. IF _Megalosaurus bucklandii_ is a nomen dubium, and IF we are
following ICZN rules, then neither Megalosauridae or Megalosauroidea are
supportable. IMHO, this is why it is better to completely ignore priority for
family-level names and anchor all clades in well-established species (i.e.,
those with excellent type specimens). Otherwise, we get a house of cards, with
the whole thing collapsing when a poorly-represented nominal species is
declared to be a nomen dubium. Titanosauridae is an example of this, and
Ceratopsidae and Hadrosauridae should follow the same path; for some reason
they've been kept alive (maybe nomenclatural stability, maybe just
sentimentality). If _Troodon_ is declared a nomen dubium, then there's no
objective reason to maintain Troodontidae in preference to Saurornithoididae
any more than we would use Deinodontidae in preference to Tyrannosauridae.
> A good solution here, but it's not always going to help -- people are
> too attached to a lot of "-idae", "-inae", etc. names.
I'm happy to retain coordinated family-level names. But I'd argue for
excluding them from the purview of the ICZN. Let PhyloCode take over families
and so forth, with ICZN retaining control of genera and species.
Boo! Scare away worms, viruses and so much more! Try Windows Live OneCare!