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Re: Hadrosaur nomenclature
As the person who is (inadvertently) responsible for this absurd little
thread, I suppose I ought to speak up. Or, "I guess *I* need to do something
here..." ;)
A) The reasoning behind synonymizing Brachylophosaurus and Maiasaura is
ultimately arbitrary, as is any decision regarding the generic disposition
of species forming a monophyletic group (as Dr. Holtz alludes). I am not
sure as to how "information on population and ontogenetic variation,
distribution, [...] preservation, sexual dimorphism, and the like" would be
brought to bear on the question, although these data certainly should be
considered in the discussion of how to recognize *species* in the fossil
record. As far as these data might apply to the recognition of clades they
apply to genera. Generally I'd say they don't, except in the species-level
work preliminary to phylogenetic analysis. I do not see that any special
consideration should be given to those names considered to be of "genus"
rank, since, as Dr. Holtz points out, there are no guidelines anywhere for
genera (apart from Paul's "rule of thumb" in _PDW_). One has but to research
the species and genera of Foraminifera to feel confident in that assertion.
C) Although the two species in question (_peeblesorum_ and
_canadiensis_) are indeed phenetically dissimilar, most, if not all of the
differences noted by k. wicks are related to the caudal retraction of the
crest and circumnarial stuff in the latter species, a point I felt was made
startlingly clear on the photographs on Prieto-Marquez's poster at SVP.
I hate to sound like a Greg Paul Parrot (_Psittacus
secondariliflightlus_, one for the Nomina Nuda Wagneri...), but if you look
at the variation in modern _Varanus_, the differences cited *pale*. Not that
that really matters, but just to make the point that the synonymy can be
justified in *anyone's* world.
Also, if _peeblesorum_ is reconstructed in such a way as to remove
the crushing evident in all illustrated specimens, it looks damned like a
_canadiensis_ without the elongate beaver-tail crest and drawn-back narial
region. This can actually be done with casts of OTM 138. So, I would say
"yes, THAT similar."
T) A substantial body of data (more than is usually presented) has been
assembled by Horner and Prieto-Marquez that indicates an exclusive
relationship exists between species _peeblesorum_ and _canadiensis_. There
is similar data, less available at present, for the other synonymies I have
adopted. Monotypic taxa (even genera) are of *no* value. All they do is take
up space with more names to remember and shuffle. In describing the
hadrosaur family tree, I see two choices for this clade: you can keep the
*redundant* genus names and make up a new name ("Maiasaurini") for the
group, or drop one of the genera, and use *nonredundant* _Brachylophosaurus_
for both. The latter option eliminates two taxa, includes no redundant taxa,
and is easier to use. Too bad it removes a cherished dinosaur genus name. So
be it, I say. We are scientists, after all, not stamp collectors.
As an aside, broadening the generic "boundaries" (whatever those are) in
this manner also brings the genera more in accord with modern taxonomy. Not
that modern generic taxonomy is any less arbitrary, of course.
G) So, yes, I would "lump" all Campanian tyrannosaurids (except
_Aublysodon_, if it is real) into _Albertosaurus_, since _Gorgosaurus_ and
_Dasplytosaurus_ are, by my understanding, monotypic. _Tyrannosaurus_
(=_Tarbosaurus_ then comes out *within* _Albertosaurus_. Whatchagonnado? Of
course, I try not to pee in the theropod pond. If you asked about say,
ceratopsians... well Chasmosaurinae would be just _Chasmosaurus_ (=
_Anchiceratops_, _Pentaceratops_) and... well, I'm not sure about
_Triceratops_ and _Torosaurus_, but the latter = _Arrhinoceratops_. It'd
probably end up being another instance of "nested genera," especially if
_utahensis_ is closer to (monotypic) _horridus_. We need better phylogenies!
Thing is, the latest K is really easy to do this in, because there is a
lot of diversity, and a lot of potential for complex tree topology. What
about other trees, like the non-hadrosaurid hadrosaur tree? Well, you either
accept monotypic genera, or abandon mandatory genera. I'm for the latter,
myself. Remember, species are what are important anyway... "units of
biodiversity" and all that... Genera don't make new species, or new genera,
and there is little point in recognizing a clade with a known membership of
one species. _caroljonesa_ and _byrdi_ are serially closer to _foulkii_,
"_Eolambia_," "_Protohadros_," and "_Hadrosaurus_" are at best little more
than hollow shells, nomenclatural artifacts holding a place for
undiscovered, and possibly nonexistent, sister species, or accumulated
morphology shared with as-yet undiscovered intermediates. At worst, they are
superfluous names appended because they are required by a set of arbitrary
rules written by a fiscally endowed Swede of nominally good parentage over
three centuries ago in the time before 99% of the theoretical structure of
modern natural history had coalesced. In some cases (certainly not those
cited here), they are no more than an outlet for the continued exercise of
vanity on the part of their authors, allowing the thrill of having ones name
entered twice in the record of life for a single discovery.
and...
U) Miscellania: First: repeat after me, everyone... May-uh-sawr-UH,
not -UHS! :)
Regarding _peeblesorum_ as the sexual dimorph of _canadiensis_... I
think George was joking.
I am not entirely sure about David Trexler's suggestion of
dimorphism in snout shape in the former, I believe the specimens may be too
distorted to be sure... we can let him decide in his paper (go David!). I
think Prieto-Marquez demonstrated strong variability, likely sexual
dimorphism, in _canadiensis_. As for _Saurolophus "blackfeetensis,"_, I am
somewhat skeptical about its distinctiveness, but. more importantly, the
type is very small, and conclusions regarding putative dimorphism in that
specimen are to be treated with caution.
Regarding the provenance of the species, I don't have the figures,
but they are only 200 km ish apart. Granted, this is "far" by Campanian
standards, but not unheard of. I would suggest that the absence of either
one in the other's vicinity is stronger evidence of (btw: Judithian is
usually reserved as a biostratigraphic adjective, not a provenance term). As
for the "different environments," off hand comments Horner's recent work
makes me wonder about the interpretation of _peeblesorum_ as an "upland"
animal. I would certainly like to see detailed documentation of the
stratigraphy. So would he, apparently... the Two Medicine is reportedly a
mess.
So, anyway, that's how I see it.
Wagner
Jonathan R. Wagner
9617 Great Hills Trail #1414
Austin, TX 78759
> K.Wicks