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Re: FAQ's



From: Larry Loen <lwloen@vnet.ibm.com>

Proposed answers:
 > 
 > How about also:
 > 
 > 1)  Are all ancient reptiles dinosaurs?

No.
 > 
 > 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.

 >   Do we know why they replaced the dinosaurs?

Not with any certainty, but the most likely explanation is simply
opportunity.  That is, they were still there, the dinosaurs
weren't, so they took advantage of the new opportunities.

This is a special case of the genral rule that when a group finds
itself in a situation with lots of unused resources, it diversifies
rapidly to ustilize those resources.
 > 
 > 3)  I heard someone say that birds were dinosaurs.  Is that true?

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).
 > 
 > 4)  What killed the dinosaurs?

This is not know with any certainty.

One widely held hypothesis is that the impact of a gigantic meteor,
probably in the Yucatan area, near the town of Chicxlub, caused
widespread disturbances that drove many groups, including the
dinosaurs (except the birds) to extinction.

Many paleontologists doubt this was, by itself, the sole cause.
Some have provided evidence of more gradual extinctions than the
impact hypothesis would allow, although others question the
significance of these results.

Other suggested causes, or contributing factors are the extreme
lowering of sea levels at the end of the Cretaceous, the massive
volcanic outpourings going on in India at the time (forming the
enormous lava plateaus called the Deccan Traps), and even disease.
 > 
 > 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.

Indeed, some, like Euoplocephalus and Pachycephalosaurus, probably
spent most of their time in the uplands, well away from major bodies
of water.
 > 
 > 6)  Dinosaurs and people lived together, right? (And, aren't there
 > tracks in Texas that
 >   prove it?)

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].
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).
 > 
 > 7)  Scientists are always saying things like "Triceratops lived in the
 >   late Cretaceous period, about 65 million years ago".  How do they know
 >   how old things like dinosaur fossils are?

By correlating lots of evidence from various sources.

First, it is possible to determine the *relative* ages of various
forms by noting the sequence in which they occur in the fossil record.
Paleontologists have done this in considerable detail, producing
complex, detailed correlations of various rock strata around the
world.  Using this scheme of correlations, Triceratops lived during
the time period called the Late Maastrichtian Epoch.

To get dates, paleontologists and geologists use radiometric dating
techniques (there are quite a number of them, each with its own
particular range of usefulness).  All of these techniques are
only usable under certain conditions, so only some rock beds can
be dated this way.  However, since the ones that are dated are
usually also part of the grand correlation scheme mentioned above,
it is possible to interpolate dates for almost all major fossil beds.

In the case of Triceratops, there are several dozen localities
of Late Maastrichtian age that have been dated.  These dates
generally range from 65 to 67 or so million years ago.  So we
conclude that Triceratops lived from 67 to 65 million years ago.

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

The peace of God be with you.