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Re: Ceratopian Family Tree



At 01:36 PM 10/29/96 -0500, Rob Meyerson wrote:

>Recent fossil finds challange this arrangement.  As I recently
>discovered, an isolated ceratopian ulna was uncovered in an Early
>Cretaceous deposit in Australia.  Due to the existing timeline, this
>ulna is considered to belong to a genus that belongs with the
>psittacosaurids.  The unusual thing about this ulna is that it bears a
>striking resemblance to the Late Cretaceous protoceratopid,
>Leptoceratops.  Since Leptoceratops is considered to be a semi-bipedal
>animal, and since this new psittacosaurid ulna is so similar to
>Leptoceratops, then it can be concluded that Leptoceratops is better
>classed as the only known Late Cretaceous psittacosaurid known at this
>time. 

        The existance of a protoceratopsian at this time would be hardly
surprising.  Cladistic theory tells us that, at any time when you find a
member of on sister taxon, but you only find the other sister higher in the
fossil record, the second sister is in fact present at the former time, you
just haven't found it yet.  These are called "ghost" lineages, lineages
which we have a logical reason to assume were around, but no fossil evidence
to back it up. 
        Think of it this way, if you find half a tennis ball in your back
yard, you can assume that, at one point, there was another half.  Of course,
the dog may have eaten the other half, so you may never find it.
        So then, because psittacosaurs were present at this time, it may be
assumed that memebers of the sister group (Ceratopsia?) which includes
proceratopsians was present, although whether or not members of the
proceratopsian clade (monophyletic?  I'm not up on my ornithiscian
phylogeny) were around or not may not be known at this time.
        I believe that the concept of "ghost lineages" has been under attack
recently, but I do not know if this is protest from the non-cladistic
community or reasoned phylogenetic argument.  Anyone familiar with the
situation, please post, as I'm sure more than a few of us are interested.

        Wagner
+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
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