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Re: FAQ's



 
 > |>  >
 > |>  > 1)  Are all ancient reptiles dinosaurs?
 > |>
 > |> No.
 > 
 > I was hoping for an amplification here about Pteranodons and
 > Elasmosaurs et. al.

I have covered some of this in another post.

I tend to prefer the more formal "pterosaurs" and "plesiosaurs".

The genus Pteranodon was one type of pterosaur.  These are
flying reptiles closely related to, but distinct from, the
dinosaurs.  Pterodactylus is another genus of pterosaur.

The pterosaurs were superficially similar to bats, but much more
diverse.
 > 
 > |>  >
 > |>  > 2)  I heard there were mammals around when the dinosaurs were alive.
 > |>  > What were they like?
 > |>
 > |> There was considerable variety.   Many were similar in body
 > |> form to shrews.  There were also forms similar to, but distinct
 > |> from, modern rodents.  In addition, opposums had already evolved
 > |> by the end of the Mesozoic.  This is just a small sample.
 > |>
 > 
 > Good answer.  Might be of interest to then follow with a brief
 > discussion of "protoreptiles" and "protomammals" (as Bakker calls
 > them in Dino Heresies) as well.

Ah yes, the so-called mammal-like reptiles, which grade almost
imperceptibly into mammals.  (The border between the mammal-like
reptiles and "real" mammals has been set by convention, but it is
an arbitrary convention, and any of several other conventions
would be equally valid).

The mammal-like reptiles were abundant and diverse in the time
before dinosaurs became dominant, starting in the Permian and
going on through the Middle Triassic (with a big drop at the
end of the Permian, along with everything else).

The early forms, called pelycosaurs, were rather reptilian
in style, and include such forms as Dimetrodon and Elaphrosaurus.
[Though these two forms were almost unique in bearing large sails
on their back - most were less spectacular].  These forms were
the dominant large animals in the Permian.

The later forms, called therapsids, were rather more mammal-like,
though some were quite bizarre by modern standards (for instance
the dicynodonts and gorgonopsids).  These froms became dominant
for a short while in the Triassic, after the grandaddy of all
extinctions almost completely eliminated the pelycosaurs (though
the earliest known therapsid is from the Permian).  One therapsid
that became extremely common in the Early Triassic was Lystrosaurus.

An interesting, and historically important, subgroup of the
therapsids was the cynodonts.  These small to medium sized
forms were very like mammals in many ways; they had several
different types of teeth (most reptiles only have one kind of
tooth), and there is reaosn to believe they had fur.  They are
not considered mammals because the detailed anatomy of their
skull retains the ancestral structure of reptiles.  Other than
that the main obvious difference from modern mammals was a more
sprawling gait (though it was more erect than in most reptiles).
But this is of little taxonomic importance, as the earliest forms
considered mammals share this primitive trait.

The earliest mammals, in the Early Jurassic, differ from the
cynodonts mostly in being smaller yet, and in having the simplified
skull and jaw structure of modern mammals.

 > |>
 > |> This is a matter of taxonomic policy, not of facts. The vast
 > |> majority of specialist agree that birds are *descended* from
 > |> dinosaurs.  For some, the cladists, this in itself is sufficient
 > |> to require that birds be classified as dinosaurs.  For others,
 > |> this is not sufficient, and they usually keep birds in a seperate
 > |> class.
 > |>
 > |> Either way, the actual *facts* of the matter are the same, the
 > |> only difference is how those facts get represented in a classification.
 > |> In thinking about this it is important to realize that classifications,
 > |> even "natural" ones, are in large part human artifacts, not facts
 > |> of nature.  (Though the underlying relationships we try to capture
 > |> in the classifications *are* facts of nature).
 > 
 > Good answer, but I think slightly too technical for newbies.  A newbie
 > would not know what "taxonomic policy" or a "cladist" is even if I sort
 > of do.

Hmm, well perhaps one of the questions in the FAQ ought to
deal with cladists versus evolutionary taxonomists.  (Cladism
does tend to come up raher alot).

As for "taxonomic policy", that is no a technical term, and my goals
here could be best met by using a clearer term if we can think of one.

What I am trying to say here is that whether birds "are" dinosaurs
or not depends on the rules one uses in judging whether a
classification acceptible or not.   [Sort of like the difference
between softball and baseball].


Is there a shorter way of saying this for beginners, or
should we substitute this longer phrase in there?
 > 
 > |>  >
 > |>  > 4)  What killed the dinosaurs?
 > |>
 > |> This is not know with any certainty.
 > |>
 > |> One widely held hypothesis ...
 > 
 > You might consider adding that it is "who survived" as well as
 > "who died" that makes this such a difficult puzzle.  A lot of
 > answers work until one tries to explain who made it through the
 > K-T barrier, not just who died, or so I read it.

Ah, good point.  Yes, that needs to be added.

It is truly a bizarre mix.  Ammonites died out, their close
relatives, the nautiloids, survived to this very day.  Dinosaurs
died out, as did pterosurs, but their close relativces the
crocodiles made it through, albeit at reduced diversity.

And when you get into the plankton (microscopic marine palnts
and animamls), the distribution gets postively strange.
 > 
 > |>  >
 > |>  > 5)  Dinosaurs lived in swamps, right?
 > |>
 > |> Some did, most did not.  The main swamp dwelling dinosaurs I know
 > |> of are Edmontosaurus, and perhaps Saurolophus.  (Both of which
 > |> are "duck-billed" dinosaurs).  Most other dinosaurs, including
 > |> the msot of the other "duck-billed" dinosaurs and the gigantic
 > |> sauropod dinosaurs were NOT swamp dwellers.
 > |>
 > 
 > For newbies, I would expand "gigantic sauropod dinosaurs" to name
 > a few famous representatives like Apatosaurs or Brachiosaurus and
 > explain exactly why scientists now ditched the swap bit (more understanding
 > of the ancient climate where the fossils were found, water pressure/
 > buried in mud arguments or whatever).

O.K, good start.

Sauropods, such as Apatosaurus (formerly called Brontosaurus)
and Brachiosaurus, have been shown to be fully terrestrial in a
number of ways.

Probably the most conclusive is the fact that the sediments where
these giants are most common - the Morrison beds of Colorado, and
the Tendaguru beds of Africa - were deposited under and extremely dry
climate.  The land at the time was dotted with seasonally dry
streams, salt flats, temporary lake beds, and miles and miles
of dry "savanna" soil (called laterites).

In conjunction with this, the actual fossils of the sauropods
are more often found in the dry soils than in the few lake beds
and permanent stream channels.  Studies of African mammal bones
shows that aquatic mammals (like hippos) tend to be found more
frequently in stream and lakebed sediments, and terrestrial
mammals (like elephants) tend to be found in soils.  This shows
that the preferences of the sauropods were similar to those of
modern elephants, not those of hippos.

Other factors include:
        - a computation of the pressure on lungs at the depth
          a sauropod might sink, showing that breathing would
          be impossible

        - a comparison of the shape of the rib cage to hippos and
          elephants - again showing closer similarity to elephants
          than to hippos.

        - foot print trails showing imprint of the full weight
          of these giants.

The inescapable conclusion is that the sauropods were as terrestrial
as elephants, and probably fed rather like giraffes, using their
long necks to reach up high into the scattered trees to feed.

Also, the way we know that Edmontosaurus was a swamp dweller
is that its bones are found almost exclusively in swamp deposits
(they are sometimes even associated with coals - which form
from peat swamps).
 > |>
 > |> No.  The tracks in Texas are all dinosaur tracks, which do
 > |> not not really look like human foot prints if one looks closely.
 > |> [That is, except for a small handful of artificially modified tracks].
 > 
 > I wouldn't mince words, here.  The few human-like ones are known (or
 > so I thought) to be fradulently altered.  Shouldn't we say so outright?

Well, not quite.

The footprints with five toes and an arch are all fakes, forget
them altogether.  (The ones I have seen are even rather *bad*
fakes, quite obviously carved).

The oblong footprints with a gross outline similar to that of
human footprints are in fact authentic trace fossils.  They are,
however, demonstrably the footprints of theropod dinosaurs with
the toe prints collapsed (due to the mud being so soft when the
prints were made).  They are in no way shape or form human prints.

My other comments below were to point out that even if these
prints were still unidentified, it would be obvious they were
not really human prints to anybody with any knowledge of tracking.
[I took one look at the photos and knew they were not human
before even reading the article].
 > 
 > |> The longest axis of these tracks is straight down the center,
 > |> rather than to the inside as in human tracks, and there is no
 > |> trace whatsoever of the 'arch' of the foot so prominant in real
 > |> human footprints (not to mention the large size of the tracks).
 > |>

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.