More Middle J stuff (was Re: Refutations and the Middle J...)

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

At 01:51 AM 2/11/99 -0000, John Jackson wrote:

>>>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)
>
>As I said up to "the end of the J", we can add Compsognathus, and that makes
>about five per 23 mys.

Okay, I paid more attention to the "before _Archaeopteryx" (a basal
Tithonian form) than to the "end of the J" bit (which would add the rest of
the Tithonian, not that that helps much).  So, yes, _Compsognathus_ would be
added to the list.

>>there are, well... nada.  Zilch.  Zippo.
>
>...other than them, that is.

Yes, that's what I had said.

>>What would probably be more accurate is that we have virtually no
>>terrestrial deposition *preserved* from the Middle Jurassic and early Late
>>Jurassic.
>>
>>Really.
>
>I'm sorry but I include Tendaguru & the Morrison.

Peter's original message, the one to which we were both responding, said:
>>To Mr. Jackson and others,
>>Please please
>
>[snip]...
>
>...>PLEASE take a look at any sort of elementary text
>>that has to do with historical geology.  I beg of you to take a look at the
>>sea level during the Middle Jurassic.  Hey, do you notice that it's very
>high?

So, in fact, I even went more inclusive and added the Oxfordian for good
measure.  I can't help it if you keep on shifting the target.

But, yes, it isn't until the Tendaguru (date insecure, somewhere in the Late
J) and the Morrison (Kimmeridgian) that we pick up a lot of terrestrial
sediment.  There really is this big gap in terrestrial deposition in many
parts of the world.  (And, mentioning the Tendaguru, small theropods again
seem to be rare.  This may in part be due to the type of excavations done at
the time: a goal of many paleontologists is to get back to Tendaguru Hill,
but political and logistical realities have proven to be BIG problems).

>>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.
>
>Excuse me but my parents taught geology, and I was going on geology field
>trips before you were born.

And my dad is an aerospace engineer, and I use to hang out at NASA's Johnson
Space Flight Center as a kid.  So?  I wouldn't consider myself qualified to
then go on to design working rocket engines.

However, given your field experience (in, I am assuming, England), how
extensive were the terrestrial outcrops for the Middle Jurassic and
Oxfordian you went to?  Any well developed paleosols?  Lots of really good
channel conglomerates?  How about some good old fashioned fine grained
lacustrine sediments: these would, after all, be great for preserved small
boned animals?

It would be great if Nature supplied us with the proper sedimentary
environments at all the proper times in Earth history to allow us to sample
the specimens we'd like.  Unfortunately, Mother Nature can be stingy.

>I remember particularly well the blockheaded
>resistance the continental drift theory met with.  I also remember the first
>time I wrote to you I had to mention your patronising habit of suggesting
>that
>ignorance was the cause of my disagreeing with you.  You're still wrong on
>that.

I would prefer to suggest ignorance rather than pigheadedness when someone
is in factual error.  Funny, but that's just the way I am.

The fact remains that, for the period of time Peter invoked (the Middle
Jurassic), terrestrial sediments are (as presently known) extremely rare.
China is the one place so far where they are known in abundance, and we know
very little about small dinosaurs from these units (_Chuandongocoelurus_
being one I forgot, as previously corrected: see, there is nothing bad about
admitting you are wrong or forgot something).

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