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Re: Hesperornis sp. nov.



Stephan Pickering (StephanPickering@cs.com) wrote:

<Needless to say, I could not disagree more...e.g., the only thing saving
Marsh's original Allosaurus fragilis from being a nomen dubium ... is the
topotype USNM 4734, a nearly complete skull/skeleton from the type
quarry.>

  Actually, this is false. No topotypes have been indicated; the only
thing saving the taxon from being an ND is the neotype USNM 6000. Any
topotype must be derived from similarity to that specimen, despite the
fact that the holotype is still clearly part of the same paradigm on the
basis of unique humeral morphology.

<There has yet been no diagnostic topotype for the specimen you name, and
I do not accept as valid nomina isolated scraps. It is my choice.>

  Indeed. As is any worker who regards *Allosaurus* with a neotype
(topotypes don't count if the holotype is garbage, unless there is a
neotype, for the simple fact that the garbage of the type cannot be shown
to pertain to any particular paradigm; the main strength in regarding the
YPM specimen in likely belonging to *Allosaurus* is a posteromedial
humeral ridge that may be general to many other taxa, but none of them
Morrison; I am not sure, but I think *Saurophaganax* also has this) can do
so to disregard any of your taxonomic works if such is the basis of
establishment. 

<An isolated bone may have plesiomorphic resemblances to other taxa, but
phylogenetic taxonomy (= rigorous databases)>

  Phylogenetic taxonomy has nothing to do with rigorous databases. Its
merely a set of taxa as anchors. One may use a phylogenetic scheme
developed from a rigorous database, but then all you're doing is naming
nodes. I could as easily use X = A < B and I have done phylogenetic
taxonomy.

<is not applicable. I have seen paper after paper re: isolated avian bones
 (mostly from the pes), with torturous measurements compared to other feet
to justify a new name.>

  A question: Are you an expert on identifying bones of various birds? Can
you tell the difference between swift and hummingbird humeri? I know
Gareth Dyke and others have spent many years working on scrap and
comparing to living and museum specimens to come to their reasoning.

<And I remind you of the plethora of nonsense names predicated upon teeth
setting aside Troodon, e.g., which is distinctive in dental morphology and
supplemented with many specimens).>

  All those supplements are teeth or toothless bones, with one
possibility, being the *Polyodontosaurus* dentary having teeth, which
still differs in tooth morphology from the type. Currie et al. have gone
through extensive collections to come to the "general" (in HIS words)
concept of tooth allocation in jaws. One must note that these
identifications are tenuous, and however distinct the holotype tooth may
be, no other taxon has yet been found with an intact, implanted crown and
root in a jaw matching that crown, reducing the possibility of getting
non-tooth body fossils to supplement the taxon's diagnosis. *Troodon*,
since Leidy described it, is known only by the one holotype tooth
(possibly premaxillary in Currie et al.'s scheme) and hundreds of shed and
broken crowns referred _from different parts of the jaw_ [as _speculated_
by Currie and others]; in fact, going through the various papers
describing Judithian teeth, all other identified premaxillary teeth
_differ_ from the type, in some ways subtle and others major, indicating
the lack of even topotypical material. All we know is that the Judithian,
like the Two Medicine, was teeming with troodontids, and it is just as
likely that the Dinosaur Park and Oldman Formations housed more than one
taxon of troodontid, just as the Nemegt and Djadockhta Formations have
more than one taxon each. This should be a note of caution in identifying
so many teeth to just one taxon or even assuming that apart from topotypic
crowns, a species based on teeth is a nomen dubium. Mammals have received
special attention, and the supported claim that even just living _species_
can differ in adult cusp shape and arrangement, makes the find of
mammalian shed or broken teeth less prone to this condition ... but I am
just as wary.

  *Troodon formosus* Leidy (1769) is, for all intents and purposes, a
nomen dubium, based and comprising of just one crown. It is possible, but
not supportable at present, that *Stenonychosaurus*, *Paronychodon* _in
partim_, and *Polyodontosaurus* are all junior synonyms, but the lack of
overlapping material horribly obfuscates this. Furthermore, in 1994,
Currie and Zhou described an adult troodontid braincase that differed from
those previously described by Russell and Currie and Currie himself in the
earlier decade. They even suggested the possibility of more than one
species.

<Phylogeny is not, to be sure, served.>

  Systematics is. Using the example given, plotopterids are by all means
real birds. We have virtually complete skeletons. No other plotopterid has
such a coracoidal morphology as the type of *Plotopterus*, which likens
its relation as a distinct form _so far_. A nomen dubium is any species
that cannot be differentiated from any other species or is based on some
material that lacks diagnostic relationship; this kind of argument might
even save *Troodon* except for the addition, in use, definition of
material consistency and availability: if any bone could belong to any
other taxon, this reduces the likelihood of the diagnostic nature of the
form, and makes the name part of a general complex of species, rather than
a valid species.

<As it is, isolated bones may give hints of relationality, but hints are
not acceptable.>

  Use your own definitions, then. Talk to Martin and Lim about this. They
have been working on it longer than you have, at least as long as reading
the paper. A paper is, after all, only a synthesis of a whole, which when
published is typically only a small part of. You miss out of the multitude
of data that they do not publish. What expertise in bird fossils allows
you to disclaim the validity of essential bits and pieces? Gareth Dyke
himself is dealing with the incredible job of wading through the London
Clay bits and pieces, and if you disagree, publish and show how this is
truly "non-diagnostic" or "non species-worthy" material. That's what Dyke
did when Stidham published on a part of a Maastrichtian jaw he referred as
a possible lorrie mandible (I would agree it is not like any edentulous
theropod mandible so far described, and certainly not like any
caenagnathid jaw). The descision to name anything based on the uniqueness
of the element is intrinsic to the study. Who better than an expert on
Antillean sloths would know the best way to diagnose an Antillean sloth?
General concepts of what is diagnostic to what degree is a matter for the
worker, and cannot, explicitly, be applied generally.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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