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First & Second messages (was: RE: first message)



Hi, Tony.

One thing I'd like to start off with: the majority of people on this lists
are, like you, not paleontologists.  They just have a great interest in the
subject.

Also, I'd like to mention the existence of our excellent archive at:
http://www.cmnh.org/fun/dinosaur-archive/index.html.
You can use it to search for answers to questions that might have been asked
before.

>
> Such a huge difference in timing to achieve the same phenomenon looks
> impossible to me. Are we that sure these fossils are actually 65
> million  years old ? How accurate is the dating process ? Is it absolute
> or does it involve some stable environmental conditions (such as the
> carbone rate in the atmosphere or the cycles of the sun...whatever could
> generate a big mistake in any dating process if ignored)? Has any
> parameter been forgotten for simplification purposes ?

You are thinking about radiocarbon (Carbon 14) dating.  This is useful only
for geologically  very recent material (thousands rather than millions of
years old), and does actually date the organic material directly.

In fact, one doesn't date the dinosaur (or other) fossils directly in the
case of truly ancient material.  Instead, you have to date the rocks
themselves.

There are a number of techniques used to date rocks:
Physical positions of rocks relative to each other, such that rocks that
were deposited first  are lower than those deposited later (this doesn't
give a numerical age date, but does give a relative age in time);
Radiometric dates, based on known rates of radioactive decay of different
non-organic naturally occurring materials;
Correlations using some types of fast-evolving, widespread, numerous, and
easily preserved fossils (plant pollen, for example), such that any rock
containing these fossils had to have been deposited between the time the
species first appeared and the time it went extinct;
The magnetic record (Earth's magnetic polarity flip-flops through time);
and others.

The best dated rocks are those in which many different lines of evidence
give the same age.

You can read about this in a bit more detail on the following course notes
from some of my classes:
http://www.geol.umd.edu/~tholtz/104Lec05.htm
http://www.geol.umd.edu/~tholtz//102Lec06.htm
http://www.geol.umd.edu/~tholtz//102Lec07.htm
http://www.geol.umd.edu/~tholtz//102Lec08.htm
http://www.geol.umd.edu/~tholtz//102Lec09.htm

> IS THERE STILL LIVING DINOSAURS ON THIS PLANET ?

Yes, and they are called 'birds'.

Some people still follow an old-fashioned system of classification in which
animals, plants, and other organisms are grouped by grade of organization.
However, in the last 40 years there has been a shift towards a new system,
one in which the principle used for the system of names is based on common
descent.

In this system (called "cladistics") all descendants from a particular
ancestor are part of a formal taxonomic group, no matter how much they
change. So, modern birds are very very specialized in their anatomy, but as
the descendants of dinosaurs they are still members of Dinosauria.
(Additionally, although modern birds are very very specialized, the earliest
birds are barely distinguishable from their closest relatives among the
other dinosaurs).

Here's a way to think about the two systems:
A student comes home from college, and now has colored their hair like a
rainbow, has lots of tattoos, and piercings all over.
The father looks at the student and says "Look at how much you've changed!
You are no longer part of this family!"
The mother says instead, and says "It doesn't matter how much you've
changed, you'll always be part of the family."
The dad represents the older (Linnean) system; the mom represents the
cladistic system.

Okay, but are there any dinosaurs OTHER than birds alive.  There is, sad to
say, no evidence for such.  All claims to the contrary have proven to be
misunderstandings, misidentifications, hoaxes, or out-right lies.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843