dino polyphyly (was RE: More on "Arbitrary" Paleontology)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 04:32 PM 6/7/99 -0700, Tom Mitchell wrote:

>>What is at stake in it [i.e., the concept of dinosaurian monophyly]?
>
>Not too much, actually.  The folks who revived the idea of dinosaurian
>monophyly in the 1970s (Galton, Bakker, Bonaparte) have sufficient enough
>other contributions to the field so that their careers are not bound up in
>its validity, if that is the sort of question you are asking.
>
>No, the career issue wasn't what I had in mind.  I have just been puzzled 
>by how completely and quickly the consensus was achieved, when there are 
>still these authoritative figures around talking as if the "dinosuar 
>duality" hypothesis was the consensus for a rather long time. (Wilford and 
>Ostrom still seem to believe in polyphyly).

Wilford is not an authority: just some guy who wrote one book on dinosaurs
(and, if memory serves, calls _Trionyx_ a dinosaur, despite the fact it is
and remains a turtle (and one still around, in fact!)).

Ostrom does not believe in dinosaur polyphyly these days: he did up to the
mid-1980s, but the work on basal ornithodirans and (later) the new specimens
of such forms as _Herrerasaurus_ and _Eoraptor_ seemed to have convinced him.

Charig is the closest to a modern authority who never did accept dinosaurian
monophyly: even some of his last papers were on the subject.

>It sounds as if dinosaur 
>taxonomy went from polyphyly to monophyly very decisively in a relatively 
>short time, without much fanfare.  Was this an issue that surfaced in the 
>public circulation of paleontological "news," or pretty much an insider's 
>affair?

As far as I can see, pretty much an inider's affair.  I never did see that
much in the public press concerning either dinosaur monophyly or dinosaur
polyphyly (and, in fact, questions about the mono-, poly-, or paraphyly of a
group seem to have had only slightly more appeal than questions of
diagenesis with the general public: the main interest seems to be in
speculation on life habits rather than on evolutionary relationships).

>So when I asked "what is at stake?" I meant: 1) What difference 
>does it make to the practice of research whether monophyly or polyphyly is 
>the prevailing consensus?

Well, working with a monophyletic groups helps to constrain things (shared
ancestral triats, determining character polarity, timing of divergences and
recognition of ghost lineages, etc.).

Of course, the (now abandoned) Simpsonian idea of mammalian polyphyly never
did slow down paleomammology

>and 2) Does it make any difference at any other 
>level--say, the public perception of dinosaur research?  Gregory Paul, for 
>one, talks about the era of polyphyly as if it were the "dark ages" of 
>dinosaurology.

I'll let Greg speak for himself on that one.  It is true that the era of
polyphyly coincides with the "dark ages" of dinosaur research: throughout
the middle decades of the century, the number of dinosaur workers declined
(as did the number of scientific papers on the subject). In the late 1960s
and early 1970s this began to reverse, with the work of Ostrom and his
students in the U.S., the Polish-Mongolian expeditions, renewed work in
China, Bonaparte's work, etc. However, even then many accepted dinosaurian
diphyly (at least).  It would seem that the possibility of dinosaurian
endothermy, the dinosaur-bird link, new clues on dinosaur behavior, etc.,
might have been at least (if not more) influential in the Dinosaur
Renaissance than thoughts on dinosaur monophyly.

By the mid-1970s Bakker & Galton and Bonaparte were reviving the concept of
a monophyletic Dinosauria, but this had much to do with the early 1970s
discoveries and descriptions of Lagosuchus and Lagerpeton (i.e., with the
discovery of a single suitable ancestral grade for all dinosaurs, rather
than having to derived theropods from one sort of thecodont, sauropodomorphs
from another, ornithischians from a third...).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661