[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Reasons to reduce Dino species count.

Sorry I lost the original message, but...

I can think of two important factors not considered by Dinogeorge in his
species estimation.

1. Dinogeorge suggests that preservational bias in favor of dinos living
near depositional environments fails to indicate they were in
areas analagous to (among other biomes) savannah and prairie grasslands.
But grass is special.  There were no savannah or prairie analogues.  The
following characteristics show why:

Grass is resistant to overgrazing.

Grass recovers quickly after a fire.  This could be a critical factor in
the survival of dinosaurs for two reasons, a) resupply of forage, b)
reestablishment of cover.  In ostriches fire has been found to be
devastating in denying them cover in nesting season.  This situation would
be even worse in a plant that could not recover as quickly.

Many grass species are C4.  Though not unique to grass (probably evolving
independently in many species!), C4 savannah grasses enjoy phenomenal
rates of growth.  I believe nothing like this productivity exists in
plants thought to be present in the Cretaceous.

Many grass species are drought resistant. This enables ostriches to be
sustained in areas of low predator density.  No similar refugium is known
from the Cretaceous.

2. Species numbers from Cretaceous depositional environments probably more
closely approximated total species numbers than fossils found in sediments
from recent times.  This is because many non-avian dinosaurs were likely
dependent on such soils as a substrate for their nests.  Because they
spent more time at such sites, they were more likely to be fossilized at
those sites than, say, a large mammal of today.  Such an effect could
definitely bias species counts.