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Re: Morrison Sauropods\etc. (long)

At 08:14 PM 7/3/2001, thescelosaurus@juno.com wrote: 
        I've pondered the same thing myself.  The Morrison especially is
amazing for the known diversity (check out the thread starting at
http://www.cmnh.org/fun/dinosaur-archive/1999May/msg00704.html for a
massive list of Morrison dinosaurs); however, I strongly suspect that if
more formations were known as well as the Morrison, we would see similar
diversity all over the world.  For example, Tendaguru has dicraeosaurids,
brachiosaurids, diplodocids, and remains that may belong to
"camarasaurids" and titanosaurids.  The Chinese MJ-LJ faunas also have a
high number of separate species, although the classification of these taxa
is currently uncertain (and it seems, from what I've read, that the
Chinese sauropods were more similar to each other than the sauropods in
the Morrison or Tendaguru were to their contemporaries).  Even in less
well-sampled formations we see great diversity; Lourinha has camarasaurids
and diplodocids, and the middle Jurassic English formations have
"cetiosaurids", diplodocoids, and macronarians (likely of the
brachiosaurid persuasion).
        So, I don't think that, in the Morrison at least, we have too many
named.  Even the sinking of a few of the questionable species still
leaves you with quite a few well supported taxa.


I think we will see a lot of species being sunk in the future (especially
in China) as more work gets done on these dinosaurs.  They seem to be on
the same kind of naming frenzy that North Americans were at the turn of the
20th Century.  People are still sorting that mess out.  I still think there
are a LOT of questionable species and even a few genera.

        The well-supported genera and species have morphological
differences that indicate different niches.  Of the Big Six
(*Apatosaurus*, *Barosaurus*, *Brachiosaurus*, *Camarasaurus*,
*Diplodocus*, and *Haplocanthosaurus*), each is very distinctive.  For
example, in feeding:
        *Apatosaurus* has peg-like teeth but relatively the shortest neck
and stoutest build of the Morrison diplodocids;
        *Barosaurus* has peg-like teeth and the longest neck of the
Morrison diplodocids;
        *Brachiosaurus* has spoon-like teeth with a long,
upwardly-directed neck and long forelimbs;
        *Camarasaurus* has spoon-like teeth but is smaller and stockier
than *Brachiosaurus*, pointing to a different feeding strategy;
        *Diplodocus* fits between the morphologies of *Apatosaurus* and
*Barosaurus*;
        *Haplocanthosaurus* likely had spoon-like teeth, combined with a
less derived body plan than the others (probably overlapping
*Camarasaurus* in its niche due to size).


These kind of make sense to me, because three are rare and the others do
seem very different in their strategies (Apato, Camara, and Diplo).  Having
stood next to the three more common ones, however, still leaves me
wondering how these animals would have gotten enough to eat.  Obviously
they did, since I was able to stand next to them.  I cannot argue that
these should be sunk, all are well enough represented and definitely
different.  However:

        Of the less common genera, we have the super-elongated
*Seismosaurus* and *Supersaurus*, mysterious *Dystrophaeus*,
apatosaur-like *Eobrontosaurus*, *Amphicoelias*, *Dystylosaurus*, and
titanosaurid-like "Apatosaurus" *minimus* (and possibly *Dyslocosaurus*
as well).  These in turn are also all distinctive.


This was what I was talking about with sauropods wandering into an
ecosystem.  Either that or they were very rare.  I wonder if some of these
will not be sunk in the future with better finds.  I am sure some will
remain dubious due to the fact that they are odd-ball material.  I have
also heard that Amphicoelias is likely not valid.  The "distinct femur" has
been showing up attached to Diplodocus specimens and maybe the neural arch
was pathological.  It is so hard to take pathological material out of the
mix.  I am sure it would kill many genera and species of dinosaur.

        This is not like *Triceratops* taxonomy, which at one point had
something like fifteen virtually indistinguishable species at the same
time and almost the same place.  These sauropods, for the most part, all
appear to have had a distinct niche.  In addition, there are some
temporal concerns in the Morrison; certain genera like *Eobrontosaurus*
and (possibly) *Haplocanthosaurus* are only known from the early Morrison
(and *Dystrophaeus may predate them all), while (I believe)
*Seismosaurus*, *Dystylosaurus*, and *Supersaurus* are late Morrison. Some
species are only upper Morrison; the largest species of *Camarasaurus* and
*Apatosaurus* are uppermost Morrison, along with the type of
*Amphicoelias*.  The faunal list doesn't tell the whole story.


No, you are right, but what is not clear to me (and other lay people) is
where in the time continuum these suckers existed.  I think that would help
sort out some of my headache.

        I'm not sure about stegosaurid diversity; I know that the
well-known ornithopods separate well by size:
*Drinker* as teeny-tiny (if Bakker is right);
*Othnielia* in the one to two meter range;
*Dryosaurus* in the three plus meter range;
*Camptosaurus* and unnamed iguanodontians at the top, probably up to seven
plus meters.
Both known ankylosaurs were fairly small.


These don't bother me.  We seem to have a range of sizes that shows that
there were many niches filled by many different types of animals.  All of
them would have been low grazers, but skull types show that they had
different feeding styles (wide mouthed, narrow mouthed, cutting beaks for
really hard plants, etc).

        The theropods also separate well by size.  At the top we have
*Torvosaurus* and the "super" allosaurs; next is regular *Allosaurus
fragilis*, followed by *Ceratosaurus*, then *Marshosaurus*.
*Stokesosaurus* and the "coelurosaurs" (*Ornitholestes*, *Coelurus*,
*Koparion*, *Palaeopteryx*, unidentified animals, etcetera) brought up
the rear.  It's not as though they were all competing for the same food
source.


I can see having to many predators since we have so much prey, but even
then, there are at least three predators over 6 meters in most
areas.  These are GIANT predators.  Luckily they have giant prey, but there
is still something unusual about having so many different large
predators.  You are not counting Bakker et al's megalosaurs, which would
bring the number of giants higher.

        On the subject of land bridges, as the members of Pangaea had not
yet fully separated, there was probably a lot of faunal mixing (see
Morrison similarities with Tendaguru and Lourinha); however, I would
think this mixing would have spread everyone out more evenly, rather than
concentrating unusual diversity in a single area.
        As I said above, I suspect that the Morrison probably preserves
the kind of diversity fairly typical of a late Jurassic dinosaur
community, and we just don't have anything comparable.-*Thescelosaurus*


If it really is typical, then it was truly amazing (not that it isn't
anyway).  I think that there must have been some really good plant material
available that was running the whole system, since it lasted so long.



Darryl Jones  <dinoguy@sympatico.ca>

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