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RE: More concerning the Triceratops/Torosaurus deal



> Hi DMLers
> 
> I mean, ok I'm just a layman, and ok, am therefore no 
> specialist, but, concerning this topic, I want to know: how 
> many "species"(taxa?) are expected to be found within a 
> "family"(taxon?) pertaining to the same clade? 

In fact, this is a relatively meaningless question. A clade is simply an
ancestor and all of its descendants, so it can be as small as a single
subpopulation of a species or as large as the total collection of living
things on the planet. There is no "expected" number.

Similarly, even using the old rank-based system, there was no fixed number:
it could vary wildly. On the one hand there were many genera with a single
species, or families with single genera; on the other there are traditional
families like Formicidae (the ants) (at 12,500 to over 20,000 species) which
are more speciose than traditional Classes like Mammalia (~4500 spp.) and
Aves (~9000 spp.), or genera like Quercus (oak trees) with 400 spp. So there
is no "expected" value.

> Why is it that _Torosaurus_ has to be _Triceratops_ adlut 
> stage? 

The arguments being made by Scanella, Horner & colleagues are based on a
number of lines of evidence, and are most certainly very reasonably
hypothesis. So it isn't that it "has to be", but rather "the data as they
interpret it point towards this".

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
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA