Refutations and the Middle J (was Re: Another Alxasaurus query & others)

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

At 07:29 PM 2/9/99 -0000, John Jackson wrote:

>>Now, to be fair, none of these studies currently *published* test what is
>>needed to refute Olshevsky's assertion: namely an analysis where
>>prosauropods and/or ornithischians are also included among the ingroups, so
>>that (in terms of the search mechanics) recovery of a
>>prosauropod-therizinosauorid clade is at least possible.
>
>The word "refute" is commonly taken in scientific circles to imply absolute
>certainty, or at least as certain as we can get about anything (as in "The
>sun will rise tomorrow").

Maybe in your circles, but not in the scientific circles that I know.  Point
A-T, as Popperians, scientists recognize that we cannot determine anything
to absolute certainty.  However, this is not the epistemology & ontology
list, so we won't go into that any further: for those interested, consult
just about any book on the philosophy of science.

Point C-G, "refute" is typically used in the scientific circles in which I
am familiar (functional morphology, sed/strat, systematics, evolutionary
biology, etc.) as the antonym of "support" (and thus a synonym of "reject").
New evidence comes around and may either support a previous hypothesis,
refute/reject it, or be equivocal.

Just hoping to clarify the terminology.

And, with regards to therizinosauroid relationships, Greg Paul has in more
recent works (e.g., The Complete Illustrated Guide to Dinosaur Skeletons)
included this (admittedly bizarre) taxon within the protoavian theropods.

In a separate post, John Jackson writes:
>>Sorry, realised just after sending the email - the supposed "gap" is from:
>>
>> the last _Coelophysis_ and _Dilophosaurus_ about 197 mya,
>>         mid Pliensbachian, early Jurassic,
>>to
>>  _Gasosaurus_, closely followed by _Proceratosaurus_ and the first
>>   _Megalosaurus_ about 173 mya, Bathonian, mid Jurassic.
>
>So yes, I was aware of it.  It's worth remembering the gap ends about 23mys
>before Archaeopteryx, and between the end of the gap and the end of the J
>there are quite a few smallish types known.

Actually, there AREN'T a lot of smallish types known.  I wish there were
(BOY, do I wish there were!!).

Between the Bathonian and the Tithonian there are very few small theropods
known.  Other than the Morrison forms (_Ornitholestes_, _Coelurus_, the
unnamed Dry Mesa maniraptoran, the unnamed cervicals of Makovicky 1997)
there are, well... nada.  Zilch.  Zippo.  At least in terms of non-teeth:
adding in the Gumirota teeth, and you get velociraptorines, troodontids,
possible tyrannosaurids (i.e., maniraptoriforms!).  Granted there is
question as to the exact affinity of these teeth (I would prefer to see
bones), but if found in Late K deposits they would be placed in these taxa
without question.

>
>Irrespective of how you define your groups it still isn't a K type, nor does
>it embody particularly well, their special features.  Why should Troodon and
>Velociraptor, which survived for all 80mys of the K (not to mention probably
>Rahonavis too) be so rare pre _Ax_?
>
See the Gumirota teeth.  They are as common (or rare) as the other taxa (if
you can call any small theropod of the post-Early J, pre-Tithonian "common").

><but how can you know that they
>>didn't live at that time when you have virtually NO terestrial deposition
>>during that time anywhere on Earth?
>
>No terrestrial deposition in a significant period (say 23mys) prior to _Ax_?
>Are you sure this is what you want to say?

He probably wanted to say something to that effect.

What would probably be more accurate is that we have virtually no
terrestrial deposition *preserved* from the Middle Jurassic and early Late
Jurassic.

Really.

China we've got: several different formations.  It is our one great hope.
Surprisingly, very little is known of small theropods of any variety,
although small ornithischians have been recovered.  Where are they hiding?
(They are doing whatever the Morrison small theropods did: we've got more
specimens of _Ceratosaurus_ or _Torvosaurus_ than any small theropod in the
Morrison!). 

The fragmentary Middle J and early Late J European stuff is primarily
marine: these are specimens which washed out into the carbonate shoals or
sank into deeper parts of the ocean.

Africa?  A big blank.  Australia and Antarctica, too.

South America has the unit which produces _Piatnitzkysaurus_ and a couple of
sauropods but no small dinosaurs yet.

This is the one epoch of dinosaur history for which North America has NO
bony fossils.  None!  From a whole epoch.

(In other words, find a new Middle Jurassic dinosaur bearing unit just about
anywhere in the world, and you are going to have more new taxa to name than
you know what to do with!)

This is why Peter really, really, really, really, really, really, really
emphasized the fact that you have to crack a book on historical geology once
or twice to understand paleontology.  PDW is good, and I keep a copy in my
office, but it is by no means the be all and end all of dinosaur
paleontology (nor intended as such).  One really *must* learn something
about geology (in general terms, and in the specifics of geologic history)
to be able to have an informed discussion on this subject.

>Bits of how many specimens of Ornitholestes are known?

Just the one individual so far.  The hand long attributed to _Ornitholestes_
has been reassigned to _Coelurus_, based on the new specimen of _Coelurus_
presented by Miles et al. at SVP.

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