Re: Fw: Most popular/common dinosaur misconceptions

[tholtz@geol.umd.edu]

> OK. But germane to the thread is the question-- is this the universally
> accepted definition of "dinosaur" among paleontologists?

Essentially, yes. Some prefer other specifiers, but refer to the same clade.

> Also--
>
> 1). I accept that cladistics is useful, and understand the practical need
> for simplifying assumptions, but feel that it is not certain (or even
> likely) that Iguanodon and Megalosaurus could in reality be traced to a
> _single_ parent organism, even if the entire historical record was in
> hand.

Ummm... So are you arguing for special creation, or for independant origin
of different lineages of Terran life? Because otherwise, any pair of
organisms will have had some unique last population representing their
most recent common ancestor, whether Meg. and Ig., you and fruitflies, or
me and E. coli.

And of course everyone recognizes the chance of actually finding this
population is vanishingly small. Nevertheless, the phrase is useful for
heuristic purposes. See numerous discussions on this list in the 1990s.

> 2). The phrase "final common ancestor" seems to me to logically refer to
> that magical Original Organism of "life arose at a single point" fame. Of
> course, the reality of "single origin" is also quite uncertain.  If one
> accepts that life could arise on other planets (ooops! undefined and
> controversial term alert!), then logically one must accept that it _could_
> have arisen more than once on Earth.

Fair enough, but the evidence at present is more consistent with a single
origin for all terrestrial life than multiple ones.

> There could even have been exchange
> of genetic information between lineages. Perhaps I could suggest "most
> _recent_ common ancestor"?

Actually, "most recent common ancestor" is by far the more common phrase.
Keesey's terminology is far rarer.

                Thomas R. Holtz, Jr.
        Senior Lecturer, Vertebrate Paleontology
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

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