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Report from Dino Fest, Part 4




             | Dino Fest was a gathering of paleontologists,
             | paleoecologists, molecular biologists, teachers,
Standardized | students and enthusiasts all interested in
Introduction | dinosaurs. We met at Indiana University / Purdue
             | University Indianapolis (IUPUI) in Indianapolis,
             | Indiana from March 24 through 26, 1994. (A good
             | time was had by all.)
             |
             | This report represents the ideas and opinions of
             | the presenter(s), not this reporter.


Thursday, March 24, 1994
9:15 a.m.

"The Place of Dinosaurs in the History of Life"
By Dale Russell (National Museum of Natural Sciences, Ottawa)

How did dinosaurs fit into the stream of life?

The model that evolution is fundamentally chaotic is not
necessarily true. Otherwise, we would not be able to detect any
evolutionary patterns through geologic history, and we do. Three
example patterns or trends that appear among living things
through geologic time are:
     1) the acceleration of biodiversity,
     2) the increase of activity levels in living things, and
     3) the increase of behavioral complexity.

Evolutionary events are accelerating through geologic time -- the
pace of life is speeding up beginning with the Precambrian.
Natural selection makes evolution a self-stimulating or
autocatalytic system best expressed with an accelerating
exponential curve through time. This model is heavily modulated
by the physical environment. Graphing the diversity of life from
its simple Precambrian forms to the approximate number of forms
present today, the midpoint falls on the age of dinosaurs.
Dinosaurs represent a middle age or medieval level. By this model,
dinosaurs are a halfway point in the complexity or "fitness" of
life through geologic time.

Mass extinctions are believed to be caused by catastrophic
events of an extraterrestrial nature. Diversity of life seems to
rebound a few million years after a given extinction. Life is
physically moderated by environmental breaks or barriers which
diversity was unable to penetrate given the conditions.

Physical area for existence is a good definer of diversity.
Comparing sea-level changes through Paleozoic time, we see the
area of continental seas was declining. As the sea levels
decreased, land biota increased. Another definer of diversity is
cold climates: as temperatures declined, so did diversity. As the
climate got worse, particularly colder and drier, and as land
area was more restricted, we find the dinosaurs present there
were physically smaller.

The physical environment was affecting the size of dinosaurs and
probably their diversity. Conversely, as the environment was
richer and the food supply was more abundant, dinosaurs are found
that are larger in size. There are apparent advantages --
inherent efficiencies to growing larger, assuming there was
enough food to feed the whole animal.

The productivity of life was greatly reduced during Mesozoic
times. Productivity to the degree of our modern equatorial
rainforests only existed in restricted high latitudes (where
incident sunlight is reduced creating a shorter growing period)
during the Mesozoic. The Mesozoic equatorial regions had some of
the largest deserts the Earth has ever known. It was a crippled
physical environment preventing dinosaurs from diversifying.

Through geologic time, there is a "pecking order" to organisms:
they spread from areas of high productivity into areas of lower
productivity. Dominant organisms appear in high energy
environments and are slowly pushed into low energy environments
as they are displaced by more modern organisms from the fertile
environments. Areas of low productivity are where we find "living
fossils" -- the once dominant organisms of ancient times. Plants
and animals of the future are in our modern deltas and other rich
environments.

Cretaceous environments were richer than earlier Mesozoic
periods, yet, on average, Cretaceous dinosaurs were smaller
compared to Jurassic dinosaurs. This suggests that Cretaceous
dinosaurs had an increased metabolic rate. This and other models
indicate that dinosaur metabolism overall seems to be increasing
through geologic time.

The paradigm for behavioral complexity is brain size; it is
geared to the biological complexity in which the animal lives.
Overall, encephalization per body size is increasing through
geologic time.

Dinosaurs did evolve: later dinosaurs could out-compete earlier
dinosaurs. Because of the continuing complexities of modern life,
dinosaurs (with their deficiencies in activity levels) could not
be competitive with modern mammals, particularly on a mainland.
We see there is a change in biological fitness in animals
through time.

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 Douglas E. Goudie                  To know all things is not permitted.
 ac941@leo.nmc.edu                               -- Horace (65 - 8 B.C.)