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Re: Weird classification

Several different issues here:

1) Lumping vs. Splitting: despite the general dinosaur community's
disregard for Greg Paul's [from our opinion] very lumping classification,
there are other paleontologists (notably invertebrate workers, but also
some paleomammalogists) who regard the one-species-per-dinosaur-genus
paradigm to be laughable. (I have actually seen them laugh about it...)

Since there is no working genericometer (by which I mean a repeatable
algorithmic way of assessing whether two species are "different at a
generic level"), there always is a certain amount of subjectivity of
assigning genus names.

Which is a long way to get around to saying that there is nothing
inherently objectionable to lumping Centrosaurinae into Centrosaurus, and
Chasmosaurinae into Triceratops (which is, I believe, the oldest genus
name of a dinosaur clearly in this clade: given the current discoveries of
basal centrosaurines and non-ceratopsid ceratopsoids with long brow horns,
Ceratops proper is not securely a chasmosaurine.)

The thing is, such extreme lumping is outside the current practice of
workers in the field, and would not be followed.

2) Adding to Renato's commentary: as I pointed out in The Dinosauria II,
this lambeosaurine/centrosaurine pattern is also followed by
albertosaurines, and it is more than temporal: there is a geographic
component. That is, regions in Laramidia where lambeosaurine and
centrosaurine taxa are more common tend to have albertosaurines; regions
with few or none do not.

This likely has a lot to do with habitat requirements of these various
subclades. At present we do not have data to assess what those
requirements are and how they different from their respective sister taxa.

Happy Boxing Day!

On Mon, December 26, 2011 9:00 am, Renato Santos wrote:
> Rescued from truncation:
> After reading about them, I have noticed something odd abuot the
> hadrosaurs= and ceratopsids:=C2=A0the genera and subfamilies=C2=A0seem
> to correspond i=n an odd way, i.e. the lambeosaurines and
> centrosaurines seem to go togethe=r (they decline at about the same
> time) and the hadrosaurines and ceratopsi=nes do (they both were the
> last around, if you know what i mean). What i'm =really trying to get
> at is this: its possible that *Pachyrhinosaurus*, Syra=cosaurus etc.
> belong to a large Centrosaurus/Monoclonius, Hypacrosaurus mer=ges w/
> lambeosaurus and corythosaurus. I believe that, also, Greg PAul did
> =this in a book. I mean, if you think about it, dinosaur
> classification shou=ldnt differ from all of God's other creatures,
> which has been brought up be=fore. If these animals were mammals or
> fish, there would (should)=C2=A0be a= major lumping. Obviously theres
> also the fact that postcranially, the cera=topsians differ very little
> from species to species. Whats the crowd's opin=ion on all this?___
> I'd suggest a comparison with the decline of perissodactyls with the
> rise of artiodactyls; horses compared with bovines as a more specific
> example. I'm not aware of much postcranial difference in the latter
> example except size, proportions and the odd anatomical detail (number
> of toes reduced in horses, width of snout in bovines).
> With all this I mean to say that an evolutionary lineage, more often
> than not, shares a number of constraints, some with an ecological
> expression, and these are usually the issue at hand when an entire
> group declines.
> As such I'm not sure there should be lumping in the dinosaur groups
> you mention: if by most accounts the selective pressure behind the
> headgear was sexual then diversity is actually underestimated as one
> cannot account for color, only shape.
> --
> Renato Santos
> http://dracontes.deviantart.com

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
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